emacs-lisp-intro-1.04/MANIFEST100666 12062 13 1205 6034011430 13736 0ustar bobuser`emacs-lisp-intro-95oct2.tar' contains: 645 Oct 2 12:25 MANIFEST 5737 Oct 2 12:14 README 11876 Jun 2 14:55 chest-of-drawers-diagram.eps 12136 Jun 2 14:55 cons-cell-diagram1.eps 12523 Jun 2 14:55 cons-cell-diagram2.eps 12420 Jun 2 14:55 cons-cell-diagram2a.eps 12984 Jun 2 14:55 cons-cell-diagram3.eps 13867 Jun 2 14:55 cons-cell-diagram4.eps 12986 Jun 2 14:55 cons-cell-diagram5.eps 671460 Oct 2 12:05 emacs-lisp-intro.texi 10252 Jun 2 14:55 lambda-diagram1.eps 10278 Jun 2 14:55 lambda-diagram2.eps 10275 Jun 2 14:55 lambda-diagram3.eps emacs-lisp-intro-1.04/README100644 12062 13 13151 6034010003 13477 0ustar bobuserREADME for tar file containing "Programming in Emacs Lisp: An Introduction" This edition, 1.04 of 2 October 1995 only corrects typographical errors in the previous editions, 1.01, 1.02, and 1.03. There are no other changes. 2 October 1995 Robert J. Chassell, bob@gnu.ai.mit.edu This is an elementary introduction to programming in Emacs Lisp for people who are not programmers, and who are not necessarily interested in programming, but who do want to customize or extend their computing environment. The tar file, `intro-emacs-lisp-1.04.tar', contains the Texinfo source file for `emacs-lisp-intro.texi'. You may convert this Texinfo file to Info to read online or typeset it to print. This tar file contains: emacs-lisp-intro.texi approx 670 kilobytes Edition 1.04 2 Oct 1995 with settings for default 8.5 by 11 inch printing, and no included PostScript figures (uses ASCII figures instead) In smallbook format, which I prefer even when printing on 8.5 by 11 inch paper, this manual prints to 276 pages; however I have set this to print in the standard 8.5 by 11 inch size. You may want to change this. This Texinfo source file, `emacs-lisp-intro.texi', formats without error using TeX version 3.1415 and `texinfo.tex' version 2.145, and `makeinfo' version 1.55. Unless you change it, the source file does not format with the obsolete `texinfo.tex' version 2.108. Also, this tar file contains the following optional Encapsulated Post Script figures. chest-of-drawers-diagram.eps 11876 bytes cons-cell-diagram1.eps 12136 cons-cell-diagram2.eps 12523 cons-cell-diagram2a.eps 12420 cons-cell-diagram3.eps 12984 cons-cell-diagram4.eps 13867 cons-cell-diagram5.eps 12986 lambda-diagram1.eps 10252 lambda-diagram2.eps 10278 lambda-diagram3.eps 10275 See the beginning of the `emacs-lisp-intro.texi' file for appropriate settings. These figures are not necessary; they are merely nice to look at --- without them you get the same figures printed with ASCII characters. Whether and how you print PostScript depends on your site. You not only need to set 'print-postscript-figures' before creating the .dvi file, but then must convert the .dvi file to .ps with a 'dvips' or equivalent command. You may also have to edit the paths for the included .eps files in 'emacs-lisp-intro.texi' to change the location from '/usr/local/lib/emacs/man/' to where ever you have put the files. On some systems you will see an error message when `psfig.tex' is loaded for the last two .eps files: ! No room for a new \write . If this happens, try `epsf.tex' instead of `psfig.tex', or try typing RET at the error; the formatting may continue successfully. Here are the instructions on formatting that you will find in the beginning of the Texinfo file 'emacs-lisp-intro.texi'. Best Wishes! @c ================ Included Figures ================ @c Set print-postscript-figures if you print PostScript figures. @c If you clear this, the ten figures will be printed as ASCII diagrams. @c (This is not relevant to Info, since Info only handles ASCII.) @c Your site may require editing changes to print PostScript; in this @c case, search for `print-postscript-figures' and make appropriate changes. @c ================ Size to Print Book ================ @c This manual can be printed in any of three different sizes. @c In the above header, set @-commands appropriately. @c 7 by 9.25 inches: @c @smallbook @c @clear largebook @c 8.5 by 11 inches: @c @set largebook @c European A4 size paper: @c @afourpaper @c @set largebook @c ================ How to Create an Info file ================ @c If you have `makeinfo' installed, run the following command @c (where % is the shell prompt): @c % makeinfo emacs-lisp-intro.texi @c or else, inside of GNU Emacs, find the `emacs-lisp-intro.texi' @c and then run: @c M-x texinfo-format-buffer @c After creating the Info file, edit your Info `dir' file @c appropriately. (The `dir' file is often in the `/usr/local/info/' @c directory.) @c ================ How to Create an HTML file ================ @c To convert to HTML format, apply `texi2html' or @c similar command to the `emacs-lisp-intro.texi' file. @c ================ How to Typeset and Print ================ @c Note: unless you change it, this file does not format with the @c obsolete `texinfo.tex 2.108'; use a more recent version. This file @c formats without error using `TeX 3.1415' and `texinfo.tex 2.145'. @c If you do not include PostScript figures, run either of the @c following command sequences, or similar commands suited to your @c system: @c % texi2dvi emacs-lisp-intro.texi @c % lpr -d emacs-lisp-intro.dvi @c or else: @c % tex emacs-lisp-intro.texi @c % texindex emacs-lisp-intro.?? @c % tex emacs-lisp-intro.texi @c % lpr -d emacs-lisp-intro.dvi @c If you include the PostScript figures, you must convert the .dvi @c file to a .ps file before printing. Run either of the @c following command sequences, or one similar: @c @c % dvips -f < emacs-lisp-intro.dvi > emacs-lisp-intro.ps @c @c or else: @c @c % postscript -p < emacs-lisp-intro.dvi > emacs-lisp-intro.ps @c @c (Note: if you edit the book so as to change the length of the @c table of contents, you may have to change the value of `pageno' below.) @c ================ End of Formatting Sections ================ emacs-lisp-intro-1.04/chest-of-drawers-diagram.eps100644 12062 13 27144 5763657267 20163 0ustar bobuser%! %%BoundingBox: 34 577 325 778 %%Title: chest-of-drawers-diagram %%CreationDate: Wed Mar 8 14:28:11 1995 %%Creator: Tgif-2.16-p4 by William Chia-Wei Cheng (william@cs.UCLA.edu) % % Due to bugs in Transcript, the 'PS-Adobe-' stuff is omitted from line 1 % /tgifdict 132 dict def tgifdict begin % % Using a zero value radius for an ellipse or an arc would result % in a non-invertible CTM matrix which causes problem when this % when this PostScript is wrapped inside other routines, such as % the multi.ps package from % ftp.ucc.su.oz.au:/pub/ps_printing/multi. You can overcome such % error by uncommenting the sole line of the procedure below: % /tgif_min_radius { % dup 0.01 lt { pop 0.01 } if } bind def /tgifellipsedict 6 dict def tgifellipsedict /mtrx matrix put /tgifellipse { tgifellipsedict begin /yrad exch def /xrad exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate xrad yrad scale 0 0 1 0 360 arc savematrix setmatrix end } def /tgifarrowtipdict 8 dict def tgifarrowtipdict /mtrx matrix put /tgifarrowtip { tgifarrowtipdict begin /dy exch def /dx exch def /h exch def /w exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate dy dx atan rotate 0 0 moveto w neg h lineto w neg h neg lineto savematrix setmatrix end } def /tgifarcdict 8 dict def tgifarcdict /mtrx matrix put /tgifarcn { tgifarcdict begin /endangle exch def /startangle exch def /yrad exch def /xrad exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate xrad yrad scale 0 0 1 startangle endangle arc savematrix setmatrix end } def /tgifarc { tgifarcdict begin /endangle exch def /startangle exch def /yrad exch def /xrad exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate xrad yrad scale 0 0 1 startangle endangle arcn savematrix setmatrix end } def /tgifsetuserscreendict 22 dict def tgifsetuserscreendict begin /tempctm matrix def /temprot matrix def /tempscale matrix def /concatprocs { /proc2 exch cvlit def /proc1 exch cvlit def /newproc proc1 length proc2 length add array def newproc 0 proc1 putinterval newproc proc1 length proc2 putinterval newproc cvx } def /resmatrix matrix def /findresolution { 72 0 resmatrix defaultmatrix dtransform /yres exch def /xres exch def xres dup mul yres dup mul add sqrt } def end /tgifsetuserscreen { tgifsetuserscreendict begin /spotfunction exch def /screenangle exch def /cellsize exch def /m tempctm currentmatrix def /rm screenangle temprot rotate def /sm cellsize dup tempscale scale def sm rm m m concatmatrix m concatmatrix pop 1 0 m dtransform /y1 exch def /x1 exch def /veclength x1 dup mul y1 dup mul add sqrt def /frequency findresolution veclength div def /newscreenangle y1 x1 atan def m 2 get m 1 get mul m 0 get m 3 get mul sub 0 gt {{neg} /spotfunction load concatprocs /spotfunction exch def } if frequency newscreenangle /spotfunction load setscreen end } def /tgifsetpatterndict 18 dict def tgifsetpatterndict begin /bitison { /ybit exch def /xbit exch def /bytevalue bstring ybit bwidth mul xbit 8 idiv add get def /mask 1 7 xbit 8 mod sub bitshift def bytevalue mask and 0 ne } def end /tgifbitpatternspotfunction { tgifsetpatterndict begin /y exch def /x exch def /xindex x 1 add 2 div bpside mul cvi def /yindex y 1 add 2 div bpside mul cvi def xindex yindex bitison { /onbits onbits 1 add def 1 } { /offbits offbits 1 add def 0 } ifelse end } def /tgifsetpattern { tgifsetpatterndict begin /cellsz exch def /angle exch def /bwidth exch def /bpside exch def /bstring exch def /onbits 0 def /offbits 0 def cellsz angle /tgifbitpatternspotfunction load tgifsetuserscreen {} settransfer offbits offbits onbits add div setgray end } def /tgifxpmdict 4 dict def /tgifbwpicstr 1 string def /tgifcolorpicstr 3 string def /tgifsetpixels { tgifxpmdict begin /pixels exch def end } def /tgifsetpix { tgifxpmdict begin pixels 3 1 roll putinterval end } def /tgifbwspot { tgifxpmdict begin /index exch def tgifbwpicstr 0 pixels index 3 mul 3 getinterval aload pop 255 mul .114 mul exch 255 mul .587 mul add exch 255 mul .299 mul add cvi put tgifbwpicstr end } def /tgifcolorspot { tgifxpmdict begin /index exch def pixels index 3 mul 3 getinterval aload pop 255 mul cvi tgifcolorpicstr 2 3 -1 roll put 255 mul cvi tgifcolorpicstr 1 3 -1 roll put 255 mul cvi tgifcolorpicstr 0 3 -1 roll put tgifcolorpicstr end } def /tgifnewcolorspot { tgifxpmdict begin /index exch def pixels index 3 mul 3 getinterval aload pop setrgbcolor end } def /tgifcolordict 4 dict def /colorimage where { pop } { /colorimage { tgifcolordict begin pop pop pop pop pop /ih exch def /iw exch def /x 0 def /y 0 def 1 1 ih { pop 1 1 iw { pop currentfile tgifbwpicstr readhexstring pop 0 get tgifnewcolorspot x y moveto 1 0 rlineto 0 1 rlineto -1 0 rlineto closepath fill /x x 1 add def } for /y y 1 add def /x 0 def } for end } def } ifelse /tgifpatdict 10 dict def /tgifpatbyte { currentdict /retstr get exch pat i cellsz mod get put } def /tgifpatproc { 0 1 widthlim {tgifpatbyte} for retstr /i i 1 add def } def /tgifpatfill { tgifpatdict begin /h exch def /w exch def /lty exch def /ltx exch def /cellsz exch def /pat exch def /widthlim w cellsz div cvi 1 sub def /retstr widthlim 1 add string def /i 0 def ltx lty translate w h true [1 0 0 1 0 0] {tgifpatproc} imagemask ltx neg lty neg translate end } def /pat1 def /pat2 <0000000000000000> def /pat3 <8000000008000000> def /pat4 <8800000022000000> def /pat5 <8800220088002200> def /pat6 <8822882288228822> def /pat7 def /pat8 <77dd77dd77dd77dd> def /pat9 <77ffddff77ffddff> def /pat10 <77ffffff77ffffff> def /pat11 <7fffffff7fffffff> def /pat12 <8040200002040800> def /pat13 <40a00000040a0000> def /pat14 def /pat15 def /pat16 def /pat17 <038448300c020101> def /pat18 <081c22c180010204> def /pat19 <8080413e080814e3> def /pat20 <8040201008040201> def /pat21 <8844221188442211> def /pat22 <77bbddee77bbddee> def /pat23 def /pat24 <7fbfdfeff7fbfdfe> def /pat25 <3e1f8fc7e3f1f87c> def /pat26 <0102040810204080> def /pat27 <1122448811224488> def /pat28 def /pat29 <83070e1c3870e0c1> def /pat30 def /pat31 <7cf8f1e3c78f1f3e> def /tgifcentertext { dup stringwidth pop 2 div neg 0 rmoveto } def /tgifrighttext { dup stringwidth pop neg 0 rmoveto } def /tgifreencsmalldict 12 dict def /tgifReEncodeSmall { tgifreencsmalldict begin /newcodesandnames exch def /newfontname exch def /basefontname exch def /basefontdict basefontname findfont def /newfont basefontdict maxlength dict def basefontdict { exch dup /FID ne { dup /Encoding eq { exch dup length array copy newfont 3 1 roll put } { exch newfont 3 1 roll put } ifelse } { pop pop } ifelse } forall newfont /FontName newfontname put newcodesandnames aload pop newcodesandnames length 2 idiv { newfont /Encoding get 3 1 roll put} repeat newfontname newfont definefont pop end } def /tgifgray { 8 1 0 72 300 32 div div tgifsetpattern } bind def /tgifboxdict 6 dict def /tgifboxstroke { tgifboxdict begin /pat def /w def /y2 exch def /x2 exch def /y1 exch def /x1 exch def 1.415 setmiterlimit w 1 eq { w setlinewidth } if pat pat1 ne pat pat2 ne and { gsave pat tgifgray } if newpath x1 y1 moveto x2 y1 lineto x2 y2 lineto x1 y2 lineto closepath pat pat2 eq { 1 setgray stroke 0 setgray } { stroke } ifelse pat pat1 ne pat pat2 ne and { grestore } if w 1 eq { 1 setlinewidth } if 1 setmiterlimit end } def /tgifboxfill { tgifboxdict begin /pat def /y2 exch def /x2 exch def /y1 exch def /x1 exch def pat pat1 ne pat pat2 ne and { gsave pat tgifgray } if newpath x1 y1 moveto x2 y1 lineto x2 y2 lineto x1 y2 lineto closepath pat pat2 eq { 1 setgray fill 0 setgray } { fill } ifelse pat pat1 ne pat pat2 ne and { grestore } if end } def end %%PageBoundingBox: 34 577 325 778 tgifdict begin /tgifsavedpage save def 1 setmiterlimit 1 setlinewidth 0 setgray 72 0 mul 72 11.00 mul translate 72 128 div 100 mul 100 div dup neg scale gsave % BOX gsave 1.415 setmiterlimit newpath 64 104 moveto 255 104 lineto 255 361 lineto 64 361 lineto closepath stroke 1 setmiterlimit grestore % POLY/OPEN-SPLINE gsave newpath 65 296 moveto 254 296 lineto stroke grestore % POLY/OPEN-SPLINE gsave newpath 63 233 moveto 255 233 lineto stroke grestore % POLY/OPEN-SPLINE gsave newpath 63 169 moveto 255 169 lineto stroke grestore % POLY/OPEN-SPLINE gsave newpath 251 362 moveto 251 361 lineto 251 379 lineto 244 379 lineto 229 361 lineto stroke grestore % OVAL gsave newpath 160 72 10 6 tgifellipse stroke grestore % POLY/OPEN-SPLINE gsave newpath 63 104 moveto 128 64 lineto 138 69 lineto stroke grestore % POLY/OPEN-SPLINE gsave newpath 255 103 moveto 190 63 lineto 180 68 lineto stroke grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 160 152 moveto (symbol name) tgifcentertext show grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 160 205 moveto (symbol definition) tgifcentertext show grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 160 272 moveto (variable name) tgifcentertext show grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 160 332 moveto (property list) tgifcentertext show grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 160 41 moveto (Chest of Drawers) tgifcentertext show grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 344 41 moveto (Contents of Drawers) show grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 344 160 moveto (bouquet) show grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 344 220 moveto ([none]) show grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 344 279 moveto (\(rose violet buttercup\)) show grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 344 337 moveto ([not described here]) show grestore % POLY/OPEN-SPLINE gsave newpath 68 362 moveto 68 361 lineto 68 379 lineto 75 379 lineto 90 361 lineto stroke grestore grestore tgifsavedpage restore end %MatchingCreationDate: Wed Mar 8 14:28:11 1995 emacs-lisp-intro-1.04/cons-cell-diagram1.eps100644 12062 13 27550 5763657267 16747 0ustar bobuser%! %%BoundingBox: 35 711 289 757 %%Title: cons-cell-diagram1 %%CreationDate: Wed Mar 8 14:26:58 1995 %%Creator: Tgif-2.16-p4 by William Chia-Wei Cheng (william@cs.UCLA.edu) % % Due to bugs in Transcript, the 'PS-Adobe-' stuff is omitted from line 1 % /tgifdict 132 dict def tgifdict begin % % Using a zero value radius for an ellipse or an arc would result % in a non-invertible CTM matrix which causes problem when this % when this PostScript is wrapped inside other routines, such as % the multi.ps package from % ftp.ucc.su.oz.au:/pub/ps_printing/multi. You can overcome such % error by uncommenting the sole line of the procedure below: % /tgif_min_radius { % dup 0.01 lt { pop 0.01 } if } bind def /tgifellipsedict 6 dict def tgifellipsedict /mtrx matrix put /tgifellipse { tgifellipsedict begin /yrad exch def /xrad exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate xrad yrad scale 0 0 1 0 360 arc savematrix setmatrix end } def /tgifarrowtipdict 8 dict def tgifarrowtipdict /mtrx matrix put /tgifarrowtip { tgifarrowtipdict begin /dy exch def /dx exch def /h exch def /w exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate dy dx atan rotate 0 0 moveto w neg h lineto w neg h neg lineto savematrix setmatrix end } def /tgifarcdict 8 dict def tgifarcdict /mtrx matrix put /tgifarcn { tgifarcdict begin /endangle exch def /startangle exch def /yrad exch def /xrad exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate xrad yrad scale 0 0 1 startangle endangle arc savematrix setmatrix end } def /tgifarc { tgifarcdict begin /endangle exch def /startangle exch def /yrad exch def /xrad exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate xrad yrad scale 0 0 1 startangle endangle arcn savematrix setmatrix end } def /tgifsetuserscreendict 22 dict def tgifsetuserscreendict begin /tempctm matrix def /temprot matrix def /tempscale matrix def /concatprocs { /proc2 exch cvlit def /proc1 exch cvlit def /newproc proc1 length proc2 length add array def newproc 0 proc1 putinterval newproc proc1 length proc2 putinterval newproc cvx } def /resmatrix matrix def /findresolution { 72 0 resmatrix defaultmatrix dtransform /yres exch def /xres exch def xres dup mul yres dup mul add sqrt } def end /tgifsetuserscreen { tgifsetuserscreendict begin /spotfunction exch def /screenangle exch def /cellsize exch def /m tempctm currentmatrix def /rm screenangle temprot rotate def /sm cellsize dup tempscale scale def sm rm m m concatmatrix m concatmatrix pop 1 0 m dtransform /y1 exch def /x1 exch def /veclength x1 dup mul y1 dup mul add sqrt def /frequency findresolution veclength div def /newscreenangle y1 x1 atan def m 2 get m 1 get mul m 0 get m 3 get mul sub 0 gt {{neg} /spotfunction load concatprocs /spotfunction exch def } if frequency newscreenangle /spotfunction load setscreen end } def /tgifsetpatterndict 18 dict def tgifsetpatterndict begin /bitison { /ybit exch def /xbit exch def /bytevalue bstring ybit bwidth mul xbit 8 idiv add get def /mask 1 7 xbit 8 mod sub bitshift def bytevalue mask and 0 ne } def end /tgifbitpatternspotfunction { tgifsetpatterndict begin /y exch def /x exch def /xindex x 1 add 2 div bpside mul cvi def /yindex y 1 add 2 div bpside mul cvi def xindex yindex bitison { /onbits onbits 1 add def 1 } { /offbits offbits 1 add def 0 } ifelse end } def /tgifsetpattern { tgifsetpatterndict begin /cellsz exch def /angle exch def /bwidth exch def /bpside exch def /bstring exch def /onbits 0 def /offbits 0 def cellsz angle /tgifbitpatternspotfunction load tgifsetuserscreen {} settransfer offbits offbits onbits add div setgray end } def /tgifxpmdict 4 dict def /tgifbwpicstr 1 string def /tgifcolorpicstr 3 string def /tgifsetpixels { tgifxpmdict begin /pixels exch def end } def /tgifsetpix { tgifxpmdict begin pixels 3 1 roll putinterval end } def /tgifbwspot { tgifxpmdict begin /index exch def tgifbwpicstr 0 pixels index 3 mul 3 getinterval aload pop 255 mul .114 mul exch 255 mul .587 mul add exch 255 mul .299 mul add cvi put tgifbwpicstr end } def /tgifcolorspot { tgifxpmdict begin /index exch def pixels index 3 mul 3 getinterval aload pop 255 mul cvi tgifcolorpicstr 2 3 -1 roll put 255 mul cvi tgifcolorpicstr 1 3 -1 roll put 255 mul cvi tgifcolorpicstr 0 3 -1 roll put tgifcolorpicstr end } def /tgifnewcolorspot { tgifxpmdict begin /index exch def pixels index 3 mul 3 getinterval aload pop setrgbcolor end } def /tgifcolordict 4 dict def /colorimage where { pop } { /colorimage { tgifcolordict begin pop pop pop pop pop /ih exch def /iw exch def /x 0 def /y 0 def 1 1 ih { pop 1 1 iw { pop currentfile tgifbwpicstr readhexstring pop 0 get tgifnewcolorspot x y moveto 1 0 rlineto 0 1 rlineto -1 0 rlineto closepath fill /x x 1 add def } for /y y 1 add def /x 0 def } for end } def } ifelse /tgifpatdict 10 dict def /tgifpatbyte { currentdict /retstr get exch pat i cellsz mod get put } def /tgifpatproc { 0 1 widthlim {tgifpatbyte} for retstr /i i 1 add def } def /tgifpatfill { tgifpatdict begin /h exch def /w exch def /lty exch def /ltx exch def /cellsz exch def /pat exch def /widthlim w cellsz div cvi 1 sub def /retstr widthlim 1 add string def /i 0 def ltx lty translate w h true [1 0 0 1 0 0] {tgifpatproc} imagemask ltx neg lty neg translate end } def /pat1 def /pat2 <0000000000000000> def /pat3 <8000000008000000> def /pat4 <8800000022000000> def /pat5 <8800220088002200> def /pat6 <8822882288228822> def /pat7 def /pat8 <77dd77dd77dd77dd> def /pat9 <77ffddff77ffddff> def /pat10 <77ffffff77ffffff> def /pat11 <7fffffff7fffffff> def /pat12 <8040200002040800> def /pat13 <40a00000040a0000> def /pat14 def /pat15 def /pat16 def /pat17 <038448300c020101> def /pat18 <081c22c180010204> def /pat19 <8080413e080814e3> def /pat20 <8040201008040201> def /pat21 <8844221188442211> def /pat22 <77bbddee77bbddee> def /pat23 def /pat24 <7fbfdfeff7fbfdfe> def /pat25 <3e1f8fc7e3f1f87c> def /pat26 <0102040810204080> def /pat27 <1122448811224488> def /pat28 def /pat29 <83070e1c3870e0c1> def /pat30 def /pat31 <7cf8f1e3c78f1f3e> def /tgifcentertext { dup stringwidth pop 2 div neg 0 rmoveto } def /tgifrighttext { dup stringwidth pop neg 0 rmoveto } def /tgifreencsmalldict 12 dict def /tgifReEncodeSmall { tgifreencsmalldict begin /newcodesandnames exch def /newfontname exch def /basefontname exch def /basefontdict basefontname findfont def /newfont basefontdict maxlength dict def basefontdict { exch dup /FID ne { dup /Encoding eq { exch dup length array copy newfont 3 1 roll put } { exch newfont 3 1 roll put } ifelse } { pop pop } ifelse } forall newfont /FontName newfontname put newcodesandnames aload pop newcodesandnames length 2 idiv { newfont /Encoding get 3 1 roll put} repeat newfontname newfont definefont pop end } def /tgifgray { 8 1 0 72 300 32 div div tgifsetpattern } bind def /tgifboxdict 6 dict def /tgifboxstroke { tgifboxdict begin /pat def /w def /y2 exch def /x2 exch def /y1 exch def /x1 exch def 1.415 setmiterlimit w 1 eq { w setlinewidth } if pat pat1 ne pat pat2 ne and { gsave pat tgifgray } if newpath x1 y1 moveto x2 y1 lineto x2 y2 lineto x1 y2 lineto closepath pat pat2 eq { 1 setgray stroke 0 setgray } { stroke } ifelse pat pat1 ne pat pat2 ne and { grestore } if w 1 eq { 1 setlinewidth } if 1 setmiterlimit end } def /tgifboxfill { tgifboxdict begin /pat def /y2 exch def /x2 exch def /y1 exch def /x1 exch def pat pat1 ne pat pat2 ne and { gsave pat tgifgray } if newpath x1 y1 moveto x2 y1 lineto x2 y2 lineto x1 y2 lineto closepath pat pat2 eq { 1 setgray fill 0 setgray } { fill } ifelse pat pat1 ne pat pat2 ne and { grestore } if end } def end %%PageBoundingBox: 35 711 289 757 tgifdict begin /tgifsavedpage save def 1 setmiterlimit 1 setlinewidth 0 setgray 72 0 mul 72 11.00 mul translate 72 128 div 100 mul 100 div dup neg scale gsave % BOX gsave 1.415 setmiterlimit newpath 66 66 moveto 130 66 lineto 130 98 lineto 66 98 lineto closepath stroke 1 setmiterlimit grestore % POLY/OPEN-SPLINE gsave newpath 98 66 moveto 98 98 lineto stroke grestore % POLY/OPEN-SPLINE gsave newpath 114 82 moveto 0 80 atan dup cos 8 mul 194 exch sub exch sin 8 mul 82 exch sub lineto stroke grestore gsave newpath 194 82 8 3 80 0 tgifarrowtip closepath fill grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 146 136 moveto (rose) show grestore % POLY/OPEN-SPLINE gsave newpath 82 82 moveto 82 131 lineto 0 48 atan dup cos 8 mul 130 exch sub exch sin 8 mul 131 exch sub lineto stroke grestore gsave newpath 130 131 8 3 48 0 tgifarrowtip closepath fill grestore % BOX gsave 1.415 setmiterlimit newpath 199 66 moveto 263 66 lineto 263 98 lineto 199 98 lineto closepath stroke 1 setmiterlimit grestore % POLY/OPEN-SPLINE gsave newpath 231 66 moveto 231 98 lineto stroke grestore % POLY/OPEN-SPLINE gsave newpath 247 82 moveto 0 93 atan dup cos 8 mul 340 exch sub exch sin 8 mul 82 exch sub lineto stroke grestore gsave newpath 340 82 8 3 93 0 tgifarrowtip closepath fill grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 279 136 moveto (violet) show grestore % POLY/OPEN-SPLINE gsave newpath 215 82 moveto 215 131 lineto 0 48 atan dup cos 8 mul 263 exch sub exch sin 8 mul 131 exch sub lineto stroke grestore gsave newpath 263 131 8 3 48 0 tgifarrowtip closepath fill grestore % BOX gsave 1.415 setmiterlimit newpath 342 64 moveto 406 64 lineto 406 96 lineto 342 96 lineto closepath stroke 1 setmiterlimit grestore % POLY/OPEN-SPLINE gsave newpath 373 64 moveto 373 96 lineto stroke grestore % POLY/OPEN-SPLINE gsave newpath 389 81 moveto 0 48 atan dup cos 8 mul 437 exch sub exch sin 8 mul 81 exch sub lineto stroke grestore gsave newpath 437 81 8 3 48 0 tgifarrowtip closepath fill grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 421 135 moveto (buttercup) show grestore % POLY/OPEN-SPLINE gsave newpath 357 81 moveto 357 130 lineto 0 48 atan dup cos 8 mul 405 exch sub exch sin 8 mul 130 exch sub lineto stroke grestore gsave newpath 405 130 8 3 48 0 tgifarrowtip closepath fill grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 449 87 moveto (nil) show grestore grestore tgifsavedpage restore end %MatchingCreationDate: Wed Mar 8 14:26:58 1995 emacs-lisp-intro-1.04/cons-cell-diagram2.eps100644 12062 13 30353 5763657267 16743 0ustar bobuser%! %%BoundingBox: 15 712 321 775 %%Title: cons-cell-diagram2 %%CreationDate: Wed Mar 8 14:26:39 1995 %%Creator: Tgif-2.16-p4 by William Chia-Wei Cheng (william@cs.UCLA.edu) % % Due to bugs in Transcript, the 'PS-Adobe-' stuff is omitted from line 1 % /tgifdict 132 dict def tgifdict begin % % Using a zero value radius for an ellipse or an arc would result % in a non-invertible CTM matrix which causes problem when this % when this PostScript is wrapped inside other routines, such as % the multi.ps package from % ftp.ucc.su.oz.au:/pub/ps_printing/multi. You can overcome such % error by uncommenting the sole line of the procedure below: % /tgif_min_radius { % dup 0.01 lt { pop 0.01 } if } bind def /tgifellipsedict 6 dict def tgifellipsedict /mtrx matrix put /tgifellipse { tgifellipsedict begin /yrad exch def /xrad exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate xrad yrad scale 0 0 1 0 360 arc savematrix setmatrix end } def /tgifarrowtipdict 8 dict def tgifarrowtipdict /mtrx matrix put /tgifarrowtip { tgifarrowtipdict begin /dy exch def /dx exch def /h exch def /w exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate dy dx atan rotate 0 0 moveto w neg h lineto w neg h neg lineto savematrix setmatrix end } def /tgifarcdict 8 dict def tgifarcdict /mtrx matrix put /tgifarcn { tgifarcdict begin /endangle exch def /startangle exch def /yrad exch def /xrad exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate xrad yrad scale 0 0 1 startangle endangle arc savematrix setmatrix end } def /tgifarc { tgifarcdict begin /endangle exch def /startangle exch def /yrad exch def /xrad exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate xrad yrad scale 0 0 1 startangle endangle arcn savematrix setmatrix end } def /tgifsetuserscreendict 22 dict def tgifsetuserscreendict begin /tempctm matrix def /temprot matrix def /tempscale matrix def /concatprocs { /proc2 exch cvlit def /proc1 exch cvlit def /newproc proc1 length proc2 length add array def newproc 0 proc1 putinterval newproc proc1 length proc2 putinterval newproc cvx } def /resmatrix matrix def /findresolution { 72 0 resmatrix defaultmatrix dtransform /yres exch def /xres exch def xres dup mul yres dup mul add sqrt } def end /tgifsetuserscreen { tgifsetuserscreendict begin /spotfunction exch def /screenangle exch def /cellsize exch def /m tempctm currentmatrix def /rm screenangle temprot rotate def /sm cellsize dup tempscale scale def sm rm m m concatmatrix m concatmatrix pop 1 0 m dtransform /y1 exch def /x1 exch def /veclength x1 dup mul y1 dup mul add sqrt def /frequency findresolution veclength div def /newscreenangle y1 x1 atan def m 2 get m 1 get mul m 0 get m 3 get mul sub 0 gt {{neg} /spotfunction load concatprocs /spotfunction exch def } if frequency newscreenangle /spotfunction load setscreen end } def /tgifsetpatterndict 18 dict def tgifsetpatterndict begin /bitison { /ybit exch def /xbit exch def /bytevalue bstring ybit bwidth mul xbit 8 idiv add get def /mask 1 7 xbit 8 mod sub bitshift def bytevalue mask and 0 ne } def end /tgifbitpatternspotfunction { tgifsetpatterndict begin /y exch def /x exch def /xindex x 1 add 2 div bpside mul cvi def /yindex y 1 add 2 div bpside mul cvi def xindex yindex bitison { /onbits onbits 1 add def 1 } { /offbits offbits 1 add def 0 } ifelse end } def /tgifsetpattern { tgifsetpatterndict begin /cellsz exch def /angle exch def /bwidth exch def /bpside exch def /bstring exch def /onbits 0 def /offbits 0 def cellsz angle /tgifbitpatternspotfunction load tgifsetuserscreen {} settransfer offbits offbits onbits add div setgray end } def /tgifxpmdict 4 dict def /tgifbwpicstr 1 string def /tgifcolorpicstr 3 string def /tgifsetpixels { tgifxpmdict begin /pixels exch def end } def /tgifsetpix { tgifxpmdict begin pixels 3 1 roll putinterval end } def /tgifbwspot { tgifxpmdict begin /index exch def tgifbwpicstr 0 pixels index 3 mul 3 getinterval aload pop 255 mul .114 mul exch 255 mul .587 mul add exch 255 mul .299 mul add cvi put tgifbwpicstr end } def /tgifcolorspot { tgifxpmdict begin /index exch def pixels index 3 mul 3 getinterval aload pop 255 mul cvi tgifcolorpicstr 2 3 -1 roll put 255 mul cvi tgifcolorpicstr 1 3 -1 roll put 255 mul cvi tgifcolorpicstr 0 3 -1 roll put tgifcolorpicstr end } def /tgifnewcolorspot { tgifxpmdict begin /index exch def pixels index 3 mul 3 getinterval aload pop setrgbcolor end } def /tgifcolordict 4 dict def /colorimage where { pop } { /colorimage { tgifcolordict begin pop pop pop pop pop /ih exch def /iw exch def /x 0 def /y 0 def 1 1 ih { pop 1 1 iw { pop currentfile tgifbwpicstr readhexstring pop 0 get tgifnewcolorspot x y moveto 1 0 rlineto 0 1 rlineto -1 0 rlineto closepath fill /x x 1 add def } for /y y 1 add def /x 0 def } for end } def } ifelse /tgifpatdict 10 dict def /tgifpatbyte { currentdict /retstr get exch pat i cellsz mod get put } def /tgifpatproc { 0 1 widthlim {tgifpatbyte} for retstr /i i 1 add def } def /tgifpatfill { tgifpatdict begin /h exch def /w exch def /lty exch def /ltx exch def /cellsz exch def /pat exch def /widthlim w cellsz div cvi 1 sub def /retstr widthlim 1 add string def /i 0 def ltx lty translate w h true [1 0 0 1 0 0] {tgifpatproc} imagemask ltx neg lty neg translate end } def /pat1 def /pat2 <0000000000000000> def /pat3 <8000000008000000> def /pat4 <8800000022000000> def /pat5 <8800220088002200> def /pat6 <8822882288228822> def /pat7 def /pat8 <77dd77dd77dd77dd> def /pat9 <77ffddff77ffddff> def /pat10 <77ffffff77ffffff> def /pat11 <7fffffff7fffffff> def /pat12 <8040200002040800> def /pat13 <40a00000040a0000> def /pat14 def /pat15 def /pat16 def /pat17 <038448300c020101> def /pat18 <081c22c180010204> def /pat19 <8080413e080814e3> def /pat20 <8040201008040201> def /pat21 <8844221188442211> def /pat22 <77bbddee77bbddee> def /pat23 def /pat24 <7fbfdfeff7fbfdfe> def /pat25 <3e1f8fc7e3f1f87c> def /pat26 <0102040810204080> def /pat27 <1122448811224488> def /pat28 def /pat29 <83070e1c3870e0c1> def /pat30 def /pat31 <7cf8f1e3c78f1f3e> def /tgifcentertext { dup stringwidth pop 2 div neg 0 rmoveto } def /tgifrighttext { dup stringwidth pop neg 0 rmoveto } def /tgifreencsmalldict 12 dict def /tgifReEncodeSmall { tgifreencsmalldict begin /newcodesandnames exch def /newfontname exch def /basefontname exch def /basefontdict basefontname findfont def /newfont basefontdict maxlength dict def basefontdict { exch dup /FID ne { dup /Encoding eq { exch dup length array copy newfont 3 1 roll put } { exch newfont 3 1 roll put } ifelse } { pop pop } ifelse } forall newfont /FontName newfontname put newcodesandnames aload pop newcodesandnames length 2 idiv { newfont /Encoding get 3 1 roll put} repeat newfontname newfont definefont pop end } def /tgifgray { 8 1 0 72 300 32 div div tgifsetpattern } bind def /tgifboxdict 6 dict def /tgifboxstroke { tgifboxdict begin /pat def /w def /y2 exch def /x2 exch def /y1 exch def /x1 exch def 1.415 setmiterlimit w 1 eq { w setlinewidth } if pat pat1 ne pat pat2 ne and { gsave pat tgifgray } if newpath x1 y1 moveto x2 y1 lineto x2 y2 lineto x1 y2 lineto closepath pat pat2 eq { 1 setgray stroke 0 setgray } { stroke } ifelse pat pat1 ne pat pat2 ne and { grestore } if w 1 eq { 1 setlinewidth } if 1 setmiterlimit end } def /tgifboxfill { tgifboxdict begin /pat def /y2 exch def /x2 exch def /y1 exch def /x1 exch def pat pat1 ne pat pat2 ne and { gsave pat tgifgray } if newpath x1 y1 moveto x2 y1 lineto x2 y2 lineto x1 y2 lineto closepath pat pat2 eq { 1 setgray fill 0 setgray } { fill } ifelse pat pat1 ne pat pat2 ne and { grestore } if end } def end %%PageBoundingBox: 15 712 321 775 tgifdict begin /tgifsavedpage save def 1 setmiterlimit 1 setlinewidth 0 setgray 72 0 mul 72 11.00 mul translate 72 128 div 100 mul 100 div dup neg scale gsave % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 32 47 moveto (bouquet) show grestore % BOX gsave 1.415 setmiterlimit newpath 122 65 moveto 186 65 lineto 186 97 lineto 122 97 lineto closepath stroke 1 setmiterlimit grestore % POLY/OPEN-SPLINE gsave newpath 154 65 moveto 154 97 lineto stroke grestore % POLY/OPEN-SPLINE gsave newpath 170 81 moveto 0 80 atan dup cos 8 mul 250 exch sub exch sin 8 mul 81 exch sub lineto stroke grestore gsave newpath 250 81 8 3 80 0 tgifarrowtip closepath fill grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 202 135 moveto (rose) show grestore % POLY/OPEN-SPLINE gsave newpath 138 81 moveto 138 130 lineto 0 48 atan dup cos 8 mul 186 exch sub exch sin 8 mul 130 exch sub lineto stroke grestore gsave newpath 186 130 8 3 48 0 tgifarrowtip closepath fill grestore % BOX gsave 1.415 setmiterlimit newpath 255 65 moveto 319 65 lineto 319 97 lineto 255 97 lineto closepath stroke 1 setmiterlimit grestore % POLY/OPEN-SPLINE gsave newpath 287 65 moveto 287 97 lineto stroke grestore % POLY/OPEN-SPLINE gsave newpath 303 81 moveto 0 93 atan dup cos 8 mul 396 exch sub exch sin 8 mul 81 exch sub lineto stroke grestore gsave newpath 396 81 8 3 93 0 tgifarrowtip closepath fill grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 335 135 moveto (violet) show grestore % POLY/OPEN-SPLINE gsave newpath 271 81 moveto 271 130 lineto 0 48 atan dup cos 8 mul 319 exch sub exch sin 8 mul 130 exch sub lineto stroke grestore gsave newpath 319 130 8 3 48 0 tgifarrowtip closepath fill grestore % BOX gsave 1.415 setmiterlimit newpath 398 63 moveto 462 63 lineto 462 95 lineto 398 95 lineto closepath stroke 1 setmiterlimit grestore % POLY/OPEN-SPLINE gsave newpath 429 63 moveto 429 95 lineto stroke grestore % POLY/OPEN-SPLINE gsave newpath 445 80 moveto 0 48 atan dup cos 8 mul 493 exch sub exch sin 8 mul 80 exch sub lineto stroke grestore gsave newpath 493 80 8 3 48 0 tgifarrowtip closepath fill grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 477 134 moveto (buttercup) show grestore % POLY/OPEN-SPLINE gsave newpath 413 80 moveto 413 129 lineto 0 48 atan dup cos 8 mul 461 exch sub exch sin 8 mul 129 exch sub lineto stroke grestore gsave newpath 461 129 8 3 48 0 tgifarrowtip closepath fill grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 505 86 moveto (nil) show grestore % POLY/OPEN-SPLINE gsave newpath 66 53 moveto 66 81 lineto 0 46 atan dup cos 8 mul 112 exch sub exch sin 8 mul 81 exch sub lineto stroke grestore gsave newpath 112 81 8 3 46 0 tgifarrowtip closepath fill grestore grestore tgifsavedpage restore end %MatchingCreationDate: Wed Mar 8 14:26:39 1995 emacs-lisp-intro-1.04/cons-cell-diagram2a.eps100644 12062 13 30204 5763657267 17077 0ustar bobuser%! %%BoundingBox: 15 702 300 767 %%Title: cons-cell-diagram2a %%CreationDate: Tue Mar 14 15:09:30 1995 %%Creator: Tgif-2.16-p4 by William Chia-Wei Cheng (william@cs.UCLA.edu) % % Due to bugs in Transcript, the 'PS-Adobe-' stuff is omitted from line 1 % /tgifdict 132 dict def tgifdict begin % % Using a zero value radius for an ellipse or an arc would result % in a non-invertible CTM matrix which causes problem when this % when this PostScript is wrapped inside other routines, such as % the multi.ps package from % ftp.ucc.su.oz.au:/pub/ps_printing/multi. You can overcome such % error by uncommenting the sole line of the procedure below: % /tgif_min_radius { % dup 0.01 lt { pop 0.01 } if } bind def /tgifellipsedict 6 dict def tgifellipsedict /mtrx matrix put /tgifellipse { tgifellipsedict begin /yrad exch def /xrad exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate xrad yrad scale 0 0 1 0 360 arc savematrix setmatrix end } def /tgifarrowtipdict 8 dict def tgifarrowtipdict /mtrx matrix put /tgifarrowtip { tgifarrowtipdict begin /dy exch def /dx exch def /h exch def /w exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate dy dx atan rotate 0 0 moveto w neg h lineto w neg h neg lineto savematrix setmatrix end } def /tgifarcdict 8 dict def tgifarcdict /mtrx matrix put /tgifarcn { tgifarcdict begin /endangle exch def /startangle exch def /yrad exch def /xrad exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate xrad yrad scale 0 0 1 startangle endangle arc savematrix setmatrix end } def /tgifarc { tgifarcdict begin /endangle exch def /startangle exch def /yrad exch def /xrad exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate xrad yrad scale 0 0 1 startangle endangle arcn savematrix setmatrix end } def /tgifsetuserscreendict 22 dict def tgifsetuserscreendict begin /tempctm matrix def /temprot matrix def /tempscale matrix def /concatprocs { /proc2 exch cvlit def /proc1 exch cvlit def /newproc proc1 length proc2 length add array def newproc 0 proc1 putinterval newproc proc1 length proc2 putinterval newproc cvx } def /resmatrix matrix def /findresolution { 72 0 resmatrix defaultmatrix dtransform /yres exch def /xres exch def xres dup mul yres dup mul add sqrt } def end /tgifsetuserscreen { tgifsetuserscreendict begin /spotfunction exch def /screenangle exch def /cellsize exch def /m tempctm currentmatrix def /rm screenangle temprot rotate def /sm cellsize dup tempscale scale def sm rm m m concatmatrix m concatmatrix pop 1 0 m dtransform /y1 exch def /x1 exch def /veclength x1 dup mul y1 dup mul add sqrt def /frequency findresolution veclength div def /newscreenangle y1 x1 atan def m 2 get m 1 get mul m 0 get m 3 get mul sub 0 gt {{neg} /spotfunction load concatprocs /spotfunction exch def } if frequency newscreenangle /spotfunction load setscreen end } def /tgifsetpatterndict 18 dict def tgifsetpatterndict begin /bitison { /ybit exch def /xbit exch def /bytevalue bstring ybit bwidth mul xbit 8 idiv add get def /mask 1 7 xbit 8 mod sub bitshift def bytevalue mask and 0 ne } def end /tgifbitpatternspotfunction { tgifsetpatterndict begin /y exch def /x exch def /xindex x 1 add 2 div bpside mul cvi def /yindex y 1 add 2 div bpside mul cvi def xindex yindex bitison { /onbits onbits 1 add def 1 } { /offbits offbits 1 add def 0 } ifelse end } def /tgifsetpattern { tgifsetpatterndict begin /cellsz exch def /angle exch def /bwidth exch def /bpside exch def /bstring exch def /onbits 0 def /offbits 0 def cellsz angle /tgifbitpatternspotfunction load tgifsetuserscreen {} settransfer offbits offbits onbits add div setgray end } def /tgifxpmdict 4 dict def /tgifbwpicstr 1 string def /tgifcolorpicstr 3 string def /tgifsetpixels { tgifxpmdict begin /pixels exch def end } def /tgifsetpix { tgifxpmdict begin pixels 3 1 roll putinterval end } def /tgifbwspot { tgifxpmdict begin /index exch def tgifbwpicstr 0 pixels index 3 mul 3 getinterval aload pop 255 mul .114 mul exch 255 mul .587 mul add exch 255 mul .299 mul add cvi put tgifbwpicstr end } def /tgifcolorspot { tgifxpmdict begin /index exch def pixels index 3 mul 3 getinterval aload pop 255 mul cvi tgifcolorpicstr 2 3 -1 roll put 255 mul cvi tgifcolorpicstr 1 3 -1 roll put 255 mul cvi tgifcolorpicstr 0 3 -1 roll put tgifcolorpicstr end } def /tgifnewcolorspot { tgifxpmdict begin /index exch def pixels index 3 mul 3 getinterval aload pop setrgbcolor end } def /tgifcolordict 4 dict def /colorimage where { pop } { /colorimage { tgifcolordict begin pop pop pop pop pop /ih exch def /iw exch def /x 0 def /y 0 def 1 1 ih { pop 1 1 iw { pop currentfile tgifbwpicstr readhexstring pop 0 get tgifnewcolorspot x y moveto 1 0 rlineto 0 1 rlineto -1 0 rlineto closepath fill /x x 1 add def } for /y y 1 add def /x 0 def } for end } def } ifelse /tgifpatdict 10 dict def /tgifpatbyte { currentdict /retstr get exch pat i cellsz mod get put } def /tgifpatproc { 0 1 widthlim {tgifpatbyte} for retstr /i i 1 add def } def /tgifpatfill { tgifpatdict begin /h exch def /w exch def /lty exch def /ltx exch def /cellsz exch def /pat exch def /widthlim w cellsz div cvi 1 sub def /retstr widthlim 1 add string def /i 0 def ltx lty translate w h true [1 0 0 1 0 0] {tgifpatproc} imagemask ltx neg lty neg translate end } def /pat1 def /pat2 <0000000000000000> def /pat3 <8000000008000000> def /pat4 <8800000022000000> def /pat5 <8800220088002200> def /pat6 <8822882288228822> def /pat7 def /pat8 <77dd77dd77dd77dd> def /pat9 <77ffddff77ffddff> def /pat10 <77ffffff77ffffff> def /pat11 <7fffffff7fffffff> def /pat12 <8040200002040800> def /pat13 <40a00000040a0000> def /pat14 def /pat15 def /pat16 def /pat17 <038448300c020101> def /pat18 <081c22c180010204> def /pat19 <8080413e080814e3> def /pat20 <8040201008040201> def /pat21 <8844221188442211> def /pat22 <77bbddee77bbddee> def /pat23 def /pat24 <7fbfdfeff7fbfdfe> def /pat25 <3e1f8fc7e3f1f87c> def /pat26 <0102040810204080> def /pat27 <1122448811224488> def /pat28 def /pat29 <83070e1c3870e0c1> def /pat30 def /pat31 <7cf8f1e3c78f1f3e> def /tgifcentertext { dup stringwidth pop 2 div neg 0 rmoveto } def /tgifrighttext { dup stringwidth pop neg 0 rmoveto } def /tgifreencsmalldict 12 dict def /tgifReEncodeSmall { tgifreencsmalldict begin /newcodesandnames exch def /newfontname exch def /basefontname exch def /basefontdict basefontname findfont def /newfont basefontdict maxlength dict def basefontdict { exch dup /FID ne { dup /Encoding eq { exch dup length array copy newfont 3 1 roll put } { exch newfont 3 1 roll put } ifelse } { pop pop } ifelse } forall newfont /FontName newfontname put newcodesandnames aload pop newcodesandnames length 2 idiv { newfont /Encoding get 3 1 roll put} repeat newfontname newfont definefont pop end } def /tgifgray { 8 1 0 72 300 32 div div tgifsetpattern } bind def /tgifboxdict 6 dict def /tgifboxstroke { tgifboxdict begin /pat def /w def /y2 exch def /x2 exch def /y1 exch def /x1 exch def 1.415 setmiterlimit w 1 eq { w setlinewidth } if pat pat1 ne pat pat2 ne and { gsave pat tgifgray } if newpath x1 y1 moveto x2 y1 lineto x2 y2 lineto x1 y2 lineto closepath pat pat2 eq { 1 setgray stroke 0 setgray } { stroke } ifelse pat pat1 ne pat pat2 ne and { grestore } if w 1 eq { 1 setlinewidth } if 1 setmiterlimit end } def /tgifboxfill { tgifboxdict begin /pat def /y2 exch def /x2 exch def /y1 exch def /x1 exch def pat pat1 ne pat pat2 ne and { gsave pat tgifgray } if newpath x1 y1 moveto x2 y1 lineto x2 y2 lineto x1 y2 lineto closepath pat pat2 eq { 1 setgray fill 0 setgray } { fill } ifelse pat pat1 ne pat pat2 ne and { grestore } if end } def end %%PageBoundingBox: 15 702 300 767 tgifdict begin /tgifsavedpage save def 1 setmiterlimit 1 setlinewidth 0 setgray 72 0 mul 72 11.00 mul translate 72 128 div 100 mul 100 div dup neg scale gsave % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 32 62 moveto (bouquet) show grestore % POLY/OPEN-SPLINE gsave newpath 64 80 moveto 64 120 lineto 0 49 atan dup cos 8 mul 113 exch sub exch sin 8 mul 120 exch sub lineto stroke grestore gsave newpath 113 120 8 3 49 0 tgifarrowtip closepath fill grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 128 110 moveto (car) show grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 128 142 moveto (rose) show grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 192 110 moveto (cdr) show grestore % OVAL gsave newpath 207 124 4 4 tgifellipse stroke grestore % POLY/OPEN-SPLINE gsave newpath 217 123 moveto 0 38 atan dup cos 8 mul 255 exch sub exch sin 8 mul 123 exch sub lineto stroke grestore gsave newpath 255 123 8 3 38 0 tgifarrowtip closepath fill grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 268 111 moveto (car) show grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 264 143 moveto (violet) show grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 332 111 moveto (cdr) show grestore % OVAL gsave newpath 347 125 4 4 tgifellipse stroke grestore % POLY/OPEN-SPLINE gsave newpath 357 124 moveto 0 38 atan dup cos 8 mul 395 exch sub exch sin 8 mul 124 exch sub lineto stroke grestore gsave newpath 395 124 8 3 38 0 tgifarrowtip closepath fill grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 408 112 moveto (car) show grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 408 136 moveto (butter-) show 408 153 moveto (cup) show grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 496 113 moveto (cdr) show grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 495 137 moveto (nil) show grestore % POLY/OPEN-SPLINE gsave newpath 178 86 moveto 178 157 lineto stroke grestore % POLY/OPEN-SPLINE gsave newpath 485 84 moveto 485 157 lineto stroke grestore % POLY/OPEN-SPLINE gsave newpath 327 85 moveto 327 157 lineto stroke grestore % BOX gsave 1.415 setmiterlimit newpath 120 86 moveto 234 86 lineto 234 157 lineto 120 157 lineto closepath stroke 1 setmiterlimit grestore % BOX gsave 1.415 setmiterlimit newpath 257 85 moveto 371 85 lineto 371 157 lineto 257 157 lineto closepath stroke 1 setmiterlimit grestore % BOX gsave 1.415 setmiterlimit newpath 397 84 moveto 531 84 lineto 531 157 lineto 397 157 lineto closepath stroke 1 setmiterlimit grestore grestore tgifsavedpage restore end %MatchingCreationDate: Tue Mar 14 15:09:30 1995 emacs-lisp-intro-1.04/cons-cell-diagram3.eps100644 12062 13 31270 5763657267 16743 0ustar bobuser%! %%BoundingBox: -1 691 324 757 %%Title: cons-cell-diagram3 %%CreationDate: Wed Mar 8 14:25:41 1995 %%Creator: Tgif-2.16-p4 by William Chia-Wei Cheng (william@cs.UCLA.edu) % % Due to bugs in Transcript, the 'PS-Adobe-' stuff is omitted from line 1 % /tgifdict 132 dict def tgifdict begin % % Using a zero value radius for an ellipse or an arc would result % in a non-invertible CTM matrix which causes problem when this % when this PostScript is wrapped inside other routines, such as % the multi.ps package from % ftp.ucc.su.oz.au:/pub/ps_printing/multi. You can overcome such % error by uncommenting the sole line of the procedure below: % /tgif_min_radius { % dup 0.01 lt { pop 0.01 } if } bind def /tgifellipsedict 6 dict def tgifellipsedict /mtrx matrix put /tgifellipse { tgifellipsedict begin /yrad exch def /xrad exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate xrad yrad scale 0 0 1 0 360 arc savematrix setmatrix end } def /tgifarrowtipdict 8 dict def tgifarrowtipdict /mtrx matrix put /tgifarrowtip { tgifarrowtipdict begin /dy exch def /dx exch def /h exch def /w exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate dy dx atan rotate 0 0 moveto w neg h lineto w neg h neg lineto savematrix setmatrix end } def /tgifarcdict 8 dict def tgifarcdict /mtrx matrix put /tgifarcn { tgifarcdict begin /endangle exch def /startangle exch def /yrad exch def /xrad exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate xrad yrad scale 0 0 1 startangle endangle arc savematrix setmatrix end } def /tgifarc { tgifarcdict begin /endangle exch def /startangle exch def /yrad exch def /xrad exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate xrad yrad scale 0 0 1 startangle endangle arcn savematrix setmatrix end } def /tgifsetuserscreendict 22 dict def tgifsetuserscreendict begin /tempctm matrix def /temprot matrix def /tempscale matrix def /concatprocs { /proc2 exch cvlit def /proc1 exch cvlit def /newproc proc1 length proc2 length add array def newproc 0 proc1 putinterval newproc proc1 length proc2 putinterval newproc cvx } def /resmatrix matrix def /findresolution { 72 0 resmatrix defaultmatrix dtransform /yres exch def /xres exch def xres dup mul yres dup mul add sqrt } def end /tgifsetuserscreen { tgifsetuserscreendict begin /spotfunction exch def /screenangle exch def /cellsize exch def /m tempctm currentmatrix def /rm screenangle temprot rotate def /sm cellsize dup tempscale scale def sm rm m m concatmatrix m concatmatrix pop 1 0 m dtransform /y1 exch def /x1 exch def /veclength x1 dup mul y1 dup mul add sqrt def /frequency findresolution veclength div def /newscreenangle y1 x1 atan def m 2 get m 1 get mul m 0 get m 3 get mul sub 0 gt {{neg} /spotfunction load concatprocs /spotfunction exch def } if frequency newscreenangle /spotfunction load setscreen end } def /tgifsetpatterndict 18 dict def tgifsetpatterndict begin /bitison { /ybit exch def /xbit exch def /bytevalue bstring ybit bwidth mul xbit 8 idiv add get def /mask 1 7 xbit 8 mod sub bitshift def bytevalue mask and 0 ne } def end /tgifbitpatternspotfunction { tgifsetpatterndict begin /y exch def /x exch def /xindex x 1 add 2 div bpside mul cvi def /yindex y 1 add 2 div bpside mul cvi def xindex yindex bitison { /onbits onbits 1 add def 1 } { /offbits offbits 1 add def 0 } ifelse end } def /tgifsetpattern { tgifsetpatterndict begin /cellsz exch def /angle exch def /bwidth exch def /bpside exch def /bstring exch def /onbits 0 def /offbits 0 def cellsz angle /tgifbitpatternspotfunction load tgifsetuserscreen {} settransfer offbits offbits onbits add div setgray end } def /tgifxpmdict 4 dict def /tgifbwpicstr 1 string def /tgifcolorpicstr 3 string def /tgifsetpixels { tgifxpmdict begin /pixels exch def end } def /tgifsetpix { tgifxpmdict begin pixels 3 1 roll putinterval end } def /tgifbwspot { tgifxpmdict begin /index exch def tgifbwpicstr 0 pixels index 3 mul 3 getinterval aload pop 255 mul .114 mul exch 255 mul .587 mul add exch 255 mul .299 mul add cvi put tgifbwpicstr end } def /tgifcolorspot { tgifxpmdict begin /index exch def pixels index 3 mul 3 getinterval aload pop 255 mul cvi tgifcolorpicstr 2 3 -1 roll put 255 mul cvi tgifcolorpicstr 1 3 -1 roll put 255 mul cvi tgifcolorpicstr 0 3 -1 roll put tgifcolorpicstr end } def /tgifnewcolorspot { tgifxpmdict begin /index exch def pixels index 3 mul 3 getinterval aload pop setrgbcolor end } def /tgifcolordict 4 dict def /colorimage where { pop } { /colorimage { tgifcolordict begin pop pop pop pop pop /ih exch def /iw exch def /x 0 def /y 0 def 1 1 ih { pop 1 1 iw { pop currentfile tgifbwpicstr readhexstring pop 0 get tgifnewcolorspot x y moveto 1 0 rlineto 0 1 rlineto -1 0 rlineto closepath fill /x x 1 add def } for /y y 1 add def /x 0 def } for end } def } ifelse /tgifpatdict 10 dict def /tgifpatbyte { currentdict /retstr get exch pat i cellsz mod get put } def /tgifpatproc { 0 1 widthlim {tgifpatbyte} for retstr /i i 1 add def } def /tgifpatfill { tgifpatdict begin /h exch def /w exch def /lty exch def /ltx exch def /cellsz exch def /pat exch def /widthlim w cellsz div cvi 1 sub def /retstr widthlim 1 add string def /i 0 def ltx lty translate w h true [1 0 0 1 0 0] {tgifpatproc} imagemask ltx neg lty neg translate end } def /pat1 def /pat2 <0000000000000000> def /pat3 <8000000008000000> def /pat4 <8800000022000000> def /pat5 <8800220088002200> def /pat6 <8822882288228822> def /pat7 def /pat8 <77dd77dd77dd77dd> def /pat9 <77ffddff77ffddff> def /pat10 <77ffffff77ffffff> def /pat11 <7fffffff7fffffff> def /pat12 <8040200002040800> def /pat13 <40a00000040a0000> def /pat14 def /pat15 def /pat16 def /pat17 <038448300c020101> def /pat18 <081c22c180010204> def /pat19 <8080413e080814e3> def /pat20 <8040201008040201> def /pat21 <8844221188442211> def /pat22 <77bbddee77bbddee> def /pat23 def /pat24 <7fbfdfeff7fbfdfe> def /pat25 <3e1f8fc7e3f1f87c> def /pat26 <0102040810204080> def /pat27 <1122448811224488> def /pat28 def /pat29 <83070e1c3870e0c1> def /pat30 def /pat31 <7cf8f1e3c78f1f3e> def /tgifcentertext { dup stringwidth pop 2 div neg 0 rmoveto } def /tgifrighttext { dup stringwidth pop neg 0 rmoveto } def /tgifreencsmalldict 12 dict def /tgifReEncodeSmall { tgifreencsmalldict begin /newcodesandnames exch def /newfontname exch def /basefontname exch def /basefontdict basefontname findfont def /newfont basefontdict maxlength dict def basefontdict { exch dup /FID ne { dup /Encoding eq { exch dup length array copy newfont 3 1 roll put } { exch newfont 3 1 roll put } ifelse } { pop pop } ifelse } forall newfont /FontName newfontname put newcodesandnames aload pop newcodesandnames length 2 idiv { newfont /Encoding get 3 1 roll put} repeat newfontname newfont definefont pop end } def /tgifgray { 8 1 0 72 300 32 div div tgifsetpattern } bind def /tgifboxdict 6 dict def /tgifboxstroke { tgifboxdict begin /pat def /w def /y2 exch def /x2 exch def /y1 exch def /x1 exch def 1.415 setmiterlimit w 1 eq { w setlinewidth } if pat pat1 ne pat pat2 ne and { gsave pat tgifgray } if newpath x1 y1 moveto x2 y1 lineto x2 y2 lineto x1 y2 lineto closepath pat pat2 eq { 1 setgray stroke 0 setgray } { stroke } ifelse pat pat1 ne pat pat2 ne and { grestore } if w 1 eq { 1 setlinewidth } if 1 setmiterlimit end } def /tgifboxfill { tgifboxdict begin /pat def /y2 exch def /x2 exch def /y1 exch def /x1 exch def pat pat1 ne pat pat2 ne and { gsave pat tgifgray } if newpath x1 y1 moveto x2 y1 lineto x2 y2 lineto x1 y2 lineto closepath pat pat2 eq { 1 setgray fill 0 setgray } { fill } ifelse pat pat1 ne pat pat2 ne and { grestore } if end } def end %%PageBoundingBox: -1 691 324 757 tgifdict begin /tgifsavedpage save def 1 setmiterlimit 1 setlinewidth 0 setgray 72 0 mul 72 11.00 mul translate 72 128 div 100 mul 100 div dup neg scale gsave % BOX gsave 1.415 setmiterlimit newpath 128 102 moveto 192 102 lineto 192 134 lineto 128 134 lineto closepath stroke 1 setmiterlimit grestore % POLY/OPEN-SPLINE gsave newpath 160 102 moveto 160 134 lineto stroke grestore % POLY/OPEN-SPLINE gsave newpath 176 124 moveto 0 80 atan dup cos 8 mul 256 exch sub exch sin 8 mul 124 exch sub lineto stroke grestore gsave newpath 256 124 8 3 80 0 tgifarrowtip closepath fill grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 208 172 moveto (rose) show grestore % POLY/OPEN-SPLINE gsave newpath 144 118 moveto 144 167 lineto 0 48 atan dup cos 8 mul 192 exch sub exch sin 8 mul 167 exch sub lineto stroke grestore gsave newpath 192 167 8 3 48 0 tgifarrowtip closepath fill grestore % BOX gsave 1.415 setmiterlimit newpath 261 102 moveto 325 102 lineto 325 134 lineto 261 134 lineto closepath stroke 1 setmiterlimit grestore % POLY/OPEN-SPLINE gsave newpath 293 102 moveto 293 134 lineto stroke grestore % POLY/OPEN-SPLINE gsave newpath 309 118 moveto 0 93 atan dup cos 8 mul 402 exch sub exch sin 8 mul 118 exch sub lineto stroke grestore gsave newpath 402 118 8 3 93 0 tgifarrowtip closepath fill grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 341 172 moveto (violet) show grestore % POLY/OPEN-SPLINE gsave newpath 277 118 moveto 277 167 lineto 0 48 atan dup cos 8 mul 325 exch sub exch sin 8 mul 167 exch sub lineto stroke grestore gsave newpath 325 167 8 3 48 0 tgifarrowtip closepath fill grestore % BOX gsave 1.415 setmiterlimit newpath 404 100 moveto 468 100 lineto 468 132 lineto 404 132 lineto closepath stroke 1 setmiterlimit grestore % POLY/OPEN-SPLINE gsave newpath 435 100 moveto 435 132 lineto stroke grestore % POLY/OPEN-SPLINE gsave newpath 451 117 moveto 0 48 atan dup cos 8 mul 499 exch sub exch sin 8 mul 117 exch sub lineto stroke grestore gsave newpath 499 117 8 3 48 0 tgifarrowtip closepath fill grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 483 171 moveto (buttercup) show grestore % POLY/OPEN-SPLINE gsave newpath 419 117 moveto 419 166 lineto 0 48 atan dup cos 8 mul 467 exch sub exch sin 8 mul 166 exch sub lineto stroke grestore gsave newpath 467 166 8 3 48 0 tgifarrowtip closepath fill grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 511 123 moveto (nil) show grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 131 80 moveto (flowers) show grestore % POLY/OPEN-SPLINE gsave newpath 210 75 moveto 237 75 lineto 237 113 lineto 0 18 atan dup cos 8 mul 255 exch sub exch sin 8 mul 113 exch sub lineto stroke grestore gsave newpath 255 113 8 3 18 0 tgifarrowtip closepath fill grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 2 80 moveto (bouquet) show grestore % POLY/OPEN-SPLINE gsave newpath 81 77 moveto 108 77 lineto 108 115 lineto 0 18 atan dup cos 8 mul 126 exch sub exch sin 8 mul 115 exch sub lineto stroke grestore gsave newpath 126 115 8 3 18 0 tgifarrowtip closepath fill grestore grestore tgifsavedpage restore end %MatchingCreationDate: Wed Mar 8 14:25:41 1995 emacs-lisp-intro-1.04/cons-cell-diagram4.eps100644 12062 13 33053 5763657267 16745 0ustar bobuser%! %%BoundingBox: 6 681 355 758 %%Title: cons-cell-diagram4 %%CreationDate: Wed Mar 8 14:25:06 1995 %%Creator: Tgif-2.16-p4 by William Chia-Wei Cheng (william@cs.UCLA.edu) % % Due to bugs in Transcript, the 'PS-Adobe-' stuff is omitted from line 1 % /tgifdict 132 dict def tgifdict begin % % Using a zero value radius for an ellipse or an arc would result % in a non-invertible CTM matrix which causes problem when this % when this PostScript is wrapped inside other routines, such as % the multi.ps package from % ftp.ucc.su.oz.au:/pub/ps_printing/multi. You can overcome such % error by uncommenting the sole line of the procedure below: % /tgif_min_radius { % dup 0.01 lt { pop 0.01 } if } bind def /tgifellipsedict 6 dict def tgifellipsedict /mtrx matrix put /tgifellipse { tgifellipsedict begin /yrad exch def /xrad exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate xrad yrad scale 0 0 1 0 360 arc savematrix setmatrix end } def /tgifarrowtipdict 8 dict def tgifarrowtipdict /mtrx matrix put /tgifarrowtip { tgifarrowtipdict begin /dy exch def /dx exch def /h exch def /w exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate dy dx atan rotate 0 0 moveto w neg h lineto w neg h neg lineto savematrix setmatrix end } def /tgifarcdict 8 dict def tgifarcdict /mtrx matrix put /tgifarcn { tgifarcdict begin /endangle exch def /startangle exch def /yrad exch def /xrad exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate xrad yrad scale 0 0 1 startangle endangle arc savematrix setmatrix end } def /tgifarc { tgifarcdict begin /endangle exch def /startangle exch def /yrad exch def /xrad exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate xrad yrad scale 0 0 1 startangle endangle arcn savematrix setmatrix end } def /tgifsetuserscreendict 22 dict def tgifsetuserscreendict begin /tempctm matrix def /temprot matrix def /tempscale matrix def /concatprocs { /proc2 exch cvlit def /proc1 exch cvlit def /newproc proc1 length proc2 length add array def newproc 0 proc1 putinterval newproc proc1 length proc2 putinterval newproc cvx } def /resmatrix matrix def /findresolution { 72 0 resmatrix defaultmatrix dtransform /yres exch def /xres exch def xres dup mul yres dup mul add sqrt } def end /tgifsetuserscreen { tgifsetuserscreendict begin /spotfunction exch def /screenangle exch def /cellsize exch def /m tempctm currentmatrix def /rm screenangle temprot rotate def /sm cellsize dup tempscale scale def sm rm m m concatmatrix m concatmatrix pop 1 0 m dtransform /y1 exch def /x1 exch def /veclength x1 dup mul y1 dup mul add sqrt def /frequency findresolution veclength div def /newscreenangle y1 x1 atan def m 2 get m 1 get mul m 0 get m 3 get mul sub 0 gt {{neg} /spotfunction load concatprocs /spotfunction exch def } if frequency newscreenangle /spotfunction load setscreen end } def /tgifsetpatterndict 18 dict def tgifsetpatterndict begin /bitison { /ybit exch def /xbit exch def /bytevalue bstring ybit bwidth mul xbit 8 idiv add get def /mask 1 7 xbit 8 mod sub bitshift def bytevalue mask and 0 ne } def end /tgifbitpatternspotfunction { tgifsetpatterndict begin /y exch def /x exch def /xindex x 1 add 2 div bpside mul cvi def /yindex y 1 add 2 div bpside mul cvi def xindex yindex bitison { /onbits onbits 1 add def 1 } { /offbits offbits 1 add def 0 } ifelse end } def /tgifsetpattern { tgifsetpatterndict begin /cellsz exch def /angle exch def /bwidth exch def /bpside exch def /bstring exch def /onbits 0 def /offbits 0 def cellsz angle /tgifbitpatternspotfunction load tgifsetuserscreen {} settransfer offbits offbits onbits add div setgray end } def /tgifxpmdict 4 dict def /tgifbwpicstr 1 string def /tgifcolorpicstr 3 string def /tgifsetpixels { tgifxpmdict begin /pixels exch def end } def /tgifsetpix { tgifxpmdict begin pixels 3 1 roll putinterval end } def /tgifbwspot { tgifxpmdict begin /index exch def tgifbwpicstr 0 pixels index 3 mul 3 getinterval aload pop 255 mul .114 mul exch 255 mul .587 mul add exch 255 mul .299 mul add cvi put tgifbwpicstr end } def /tgifcolorspot { tgifxpmdict begin /index exch def pixels index 3 mul 3 getinterval aload pop 255 mul cvi tgifcolorpicstr 2 3 -1 roll put 255 mul cvi tgifcolorpicstr 1 3 -1 roll put 255 mul cvi tgifcolorpicstr 0 3 -1 roll put tgifcolorpicstr end } def /tgifnewcolorspot { tgifxpmdict begin /index exch def pixels index 3 mul 3 getinterval aload pop setrgbcolor end } def /tgifcolordict 4 dict def /colorimage where { pop } { /colorimage { tgifcolordict begin pop pop pop pop pop /ih exch def /iw exch def /x 0 def /y 0 def 1 1 ih { pop 1 1 iw { pop currentfile tgifbwpicstr readhexstring pop 0 get tgifnewcolorspot x y moveto 1 0 rlineto 0 1 rlineto -1 0 rlineto closepath fill /x x 1 add def } for /y y 1 add def /x 0 def } for end } def } ifelse /tgifpatdict 10 dict def /tgifpatbyte { currentdict /retstr get exch pat i cellsz mod get put } def /tgifpatproc { 0 1 widthlim {tgifpatbyte} for retstr /i i 1 add def } def /tgifpatfill { tgifpatdict begin /h exch def /w exch def /lty exch def /ltx exch def /cellsz exch def /pat exch def /widthlim w cellsz div cvi 1 sub def /retstr widthlim 1 add string def /i 0 def ltx lty translate w h true [1 0 0 1 0 0] {tgifpatproc} imagemask ltx neg lty neg translate end } def /pat1 def /pat2 <0000000000000000> def /pat3 <8000000008000000> def /pat4 <8800000022000000> def /pat5 <8800220088002200> def /pat6 <8822882288228822> def /pat7 def /pat8 <77dd77dd77dd77dd> def /pat9 <77ffddff77ffddff> def /pat10 <77ffffff77ffffff> def /pat11 <7fffffff7fffffff> def /pat12 <8040200002040800> def /pat13 <40a00000040a0000> def /pat14 def /pat15 def /pat16 def /pat17 <038448300c020101> def /pat18 <081c22c180010204> def /pat19 <8080413e080814e3> def /pat20 <8040201008040201> def /pat21 <8844221188442211> def /pat22 <77bbddee77bbddee> def /pat23 def /pat24 <7fbfdfeff7fbfdfe> def /pat25 <3e1f8fc7e3f1f87c> def /pat26 <0102040810204080> def /pat27 <1122448811224488> def /pat28 def /pat29 <83070e1c3870e0c1> def /pat30 def /pat31 <7cf8f1e3c78f1f3e> def /tgifcentertext { dup stringwidth pop 2 div neg 0 rmoveto } def /tgifrighttext { dup stringwidth pop neg 0 rmoveto } def /tgifreencsmalldict 12 dict def /tgifReEncodeSmall { tgifreencsmalldict begin /newcodesandnames exch def /newfontname exch def /basefontname exch def /basefontdict basefontname findfont def /newfont basefontdict maxlength dict def basefontdict { exch dup /FID ne { dup /Encoding eq { exch dup length array copy newfont 3 1 roll put } { exch newfont 3 1 roll put } ifelse } { pop pop } ifelse } forall newfont /FontName newfontname put newcodesandnames aload pop newcodesandnames length 2 idiv { newfont /Encoding get 3 1 roll put} repeat newfontname newfont definefont pop end } def /tgifgray { 8 1 0 72 300 32 div div tgifsetpattern } bind def /tgifboxdict 6 dict def /tgifboxstroke { tgifboxdict begin /pat def /w def /y2 exch def /x2 exch def /y1 exch def /x1 exch def 1.415 setmiterlimit w 1 eq { w setlinewidth } if pat pat1 ne pat pat2 ne and { gsave pat tgifgray } if newpath x1 y1 moveto x2 y1 lineto x2 y2 lineto x1 y2 lineto closepath pat pat2 eq { 1 setgray stroke 0 setgray } { stroke } ifelse pat pat1 ne pat pat2 ne and { grestore } if w 1 eq { 1 setlinewidth } if 1 setmiterlimit end } def /tgifboxfill { tgifboxdict begin /pat def /y2 exch def /x2 exch def /y1 exch def /x1 exch def pat pat1 ne pat pat2 ne and { gsave pat tgifgray } if newpath x1 y1 moveto x2 y1 lineto x2 y2 lineto x1 y2 lineto closepath pat pat2 eq { 1 setgray fill 0 setgray } { fill } ifelse pat pat1 ne pat pat2 ne and { grestore } if end } def end %%PageBoundingBox: 6 681 355 758 tgifdict begin /tgifsavedpage save def 1 setmiterlimit 1 setlinewidth 0 setgray 72 0 mul 72 11.00 mul translate 72 128 div 100 mul 100 div dup neg scale gsave % POLY/OPEN-SPLINE gsave newpath 274 102 moveto 274 134 lineto stroke grestore % POLY/OPEN-SPLINE gsave newpath 289 122 moveto 0 56 atan dup cos 8 mul 345 exch sub exch sin 8 mul 122 exch sub lineto stroke grestore gsave newpath 345 122 8 3 56 0 tgifarrowtip closepath fill grestore % BOX gsave 1.415 setmiterlimit newpath 350 100 moveto 414 100 lineto 414 132 lineto 350 132 lineto closepath stroke 1 setmiterlimit grestore % POLY/OPEN-SPLINE gsave newpath 382 100 moveto 382 132 lineto stroke grestore % POLY/OPEN-SPLINE gsave newpath 397 114 moveto 0 59 atan dup cos 8 mul 456 exch sub exch sin 8 mul 114 exch sub lineto stroke grestore gsave newpath 456 114 8 3 59 0 tgifarrowtip closepath fill grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 430 170 moveto (violet) show grestore % POLY/OPEN-SPLINE gsave newpath 366 116 moveto 366 165 lineto 0 48 atan dup cos 8 mul 414 exch sub exch sin 8 mul 165 exch sub lineto stroke grestore gsave newpath 414 165 8 3 48 0 tgifarrowtip closepath fill grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 219 78 moveto (flowers) show grestore % POLY/OPEN-SPLINE gsave newpath 298 73 moveto 325 73 lineto 325 111 lineto 0 18 atan dup cos 8 mul 343 exch sub exch sin 8 mul 111 exch sub lineto stroke grestore gsave newpath 343 111 8 3 18 0 tgifarrowtip closepath fill grestore % BOX gsave 1.415 setmiterlimit newpath 459 95 moveto 523 95 lineto 523 127 lineto 459 127 lineto closepath stroke 1 setmiterlimit grestore % POLY/OPEN-SPLINE gsave newpath 490 95 moveto 490 127 lineto stroke grestore % POLY/OPEN-SPLINE gsave newpath 506 112 moveto 0 48 atan dup cos 8 mul 554 exch sub exch sin 8 mul 112 exch sub lineto stroke grestore gsave newpath 554 112 8 3 48 0 tgifarrowtip closepath fill grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 566 118 moveto (nil) show grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 538 151 moveto (buttercup) show grestore % POLY/OPEN-SPLINE gsave newpath 474 109 moveto 474 146 lineto 0 48 atan dup cos 8 mul 522 exch sub exch sin 8 mul 146 exch sub lineto stroke grestore gsave newpath 522 146 8 3 48 0 tgifarrowtip closepath fill grestore % BOX gsave 1.415 setmiterlimit newpath 244 102 moveto 308 102 lineto 308 134 lineto 244 134 lineto closepath stroke 1 setmiterlimit grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 324 189 moveto (rose) show grestore % POLY/OPEN-SPLINE gsave newpath 260 117 moveto 260 184 lineto 0 48 atan dup cos 8 mul 308 exch sub exch sin 8 mul 184 exch sub lineto stroke grestore gsave newpath 308 184 8 3 48 0 tgifarrowtip closepath fill grestore % BOX gsave 1.415 setmiterlimit newpath 146 101 moveto 210 101 lineto 210 133 lineto 146 133 lineto closepath stroke 1 setmiterlimit grestore % POLY/OPEN-SPLINE gsave newpath 177 101 moveto 177 133 lineto stroke grestore % POLY/OPEN-SPLINE gsave newpath 193 118 moveto 0 48 atan dup cos 8 mul 241 exch sub exch sin 8 mul 118 exch sub lineto stroke grestore gsave newpath 241 118 8 3 48 0 tgifarrowtip closepath fill grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 187 178 moveto (lilly) show grestore % POLY/OPEN-SPLINE gsave newpath 163 118 moveto 163 171 lineto 0 18 atan dup cos 8 mul 181 exch sub exch sin 8 mul 171 exch sub lineto stroke grestore gsave newpath 181 171 8 3 18 0 tgifarrowtip closepath fill grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 16 78 moveto (bouquet) show grestore % POLY/OPEN-SPLINE gsave newpath 95 73 moveto 122 73 lineto 122 111 lineto 0 18 atan dup cos 8 mul 140 exch sub exch sin 8 mul 111 exch sub lineto stroke grestore gsave newpath 140 111 8 3 18 0 tgifarrowtip closepath fill grestore grestore tgifsavedpage restore end %MatchingCreationDate: Wed Mar 8 14:25:06 1995 emacs-lisp-intro-1.04/cons-cell-diagram5.eps100644 12062 13 31272 5763657267 16747 0ustar bobuser%! %%BoundingBox: 15 680 305 764 %%Title: cons-cell-diagram5 %%CreationDate: Wed Mar 8 14:27:28 1995 %%Creator: Tgif-2.16-p4 by William Chia-Wei Cheng (william@cs.UCLA.edu) % % Due to bugs in Transcript, the 'PS-Adobe-' stuff is omitted from line 1 % /tgifdict 132 dict def tgifdict begin % % Using a zero value radius for an ellipse or an arc would result % in a non-invertible CTM matrix which causes problem when this % when this PostScript is wrapped inside other routines, such as % the multi.ps package from % ftp.ucc.su.oz.au:/pub/ps_printing/multi. You can overcome such % error by uncommenting the sole line of the procedure below: % /tgif_min_radius { % dup 0.01 lt { pop 0.01 } if } bind def /tgifellipsedict 6 dict def tgifellipsedict /mtrx matrix put /tgifellipse { tgifellipsedict begin /yrad exch def /xrad exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate xrad yrad scale 0 0 1 0 360 arc savematrix setmatrix end } def /tgifarrowtipdict 8 dict def tgifarrowtipdict /mtrx matrix put /tgifarrowtip { tgifarrowtipdict begin /dy exch def /dx exch def /h exch def /w exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate dy dx atan rotate 0 0 moveto w neg h lineto w neg h neg lineto savematrix setmatrix end } def /tgifarcdict 8 dict def tgifarcdict /mtrx matrix put /tgifarcn { tgifarcdict begin /endangle exch def /startangle exch def /yrad exch def /xrad exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate xrad yrad scale 0 0 1 startangle endangle arc savematrix setmatrix end } def /tgifarc { tgifarcdict begin /endangle exch def /startangle exch def /yrad exch def /xrad exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate xrad yrad scale 0 0 1 startangle endangle arcn savematrix setmatrix end } def /tgifsetuserscreendict 22 dict def tgifsetuserscreendict begin /tempctm matrix def /temprot matrix def /tempscale matrix def /concatprocs { /proc2 exch cvlit def /proc1 exch cvlit def /newproc proc1 length proc2 length add array def newproc 0 proc1 putinterval newproc proc1 length proc2 putinterval newproc cvx } def /resmatrix matrix def /findresolution { 72 0 resmatrix defaultmatrix dtransform /yres exch def /xres exch def xres dup mul yres dup mul add sqrt } def end /tgifsetuserscreen { tgifsetuserscreendict begin /spotfunction exch def /screenangle exch def /cellsize exch def /m tempctm currentmatrix def /rm screenangle temprot rotate def /sm cellsize dup tempscale scale def sm rm m m concatmatrix m concatmatrix pop 1 0 m dtransform /y1 exch def /x1 exch def /veclength x1 dup mul y1 dup mul add sqrt def /frequency findresolution veclength div def /newscreenangle y1 x1 atan def m 2 get m 1 get mul m 0 get m 3 get mul sub 0 gt {{neg} /spotfunction load concatprocs /spotfunction exch def } if frequency newscreenangle /spotfunction load setscreen end } def /tgifsetpatterndict 18 dict def tgifsetpatterndict begin /bitison { /ybit exch def /xbit exch def /bytevalue bstring ybit bwidth mul xbit 8 idiv add get def /mask 1 7 xbit 8 mod sub bitshift def bytevalue mask and 0 ne } def end /tgifbitpatternspotfunction { tgifsetpatterndict begin /y exch def /x exch def /xindex x 1 add 2 div bpside mul cvi def /yindex y 1 add 2 div bpside mul cvi def xindex yindex bitison { /onbits onbits 1 add def 1 } { /offbits offbits 1 add def 0 } ifelse end } def /tgifsetpattern { tgifsetpatterndict begin /cellsz exch def /angle exch def /bwidth exch def /bpside exch def /bstring exch def /onbits 0 def /offbits 0 def cellsz angle /tgifbitpatternspotfunction load tgifsetuserscreen {} settransfer offbits offbits onbits add div setgray end } def /tgifxpmdict 4 dict def /tgifbwpicstr 1 string def /tgifcolorpicstr 3 string def /tgifsetpixels { tgifxpmdict begin /pixels exch def end } def /tgifsetpix { tgifxpmdict begin pixels 3 1 roll putinterval end } def /tgifbwspot { tgifxpmdict begin /index exch def tgifbwpicstr 0 pixels index 3 mul 3 getinterval aload pop 255 mul .114 mul exch 255 mul .587 mul add exch 255 mul .299 mul add cvi put tgifbwpicstr end } def /tgifcolorspot { tgifxpmdict begin /index exch def pixels index 3 mul 3 getinterval aload pop 255 mul cvi tgifcolorpicstr 2 3 -1 roll put 255 mul cvi tgifcolorpicstr 1 3 -1 roll put 255 mul cvi tgifcolorpicstr 0 3 -1 roll put tgifcolorpicstr end } def /tgifnewcolorspot { tgifxpmdict begin /index exch def pixels index 3 mul 3 getinterval aload pop setrgbcolor end } def /tgifcolordict 4 dict def /colorimage where { pop } { /colorimage { tgifcolordict begin pop pop pop pop pop /ih exch def /iw exch def /x 0 def /y 0 def 1 1 ih { pop 1 1 iw { pop currentfile tgifbwpicstr readhexstring pop 0 get tgifnewcolorspot x y moveto 1 0 rlineto 0 1 rlineto -1 0 rlineto closepath fill /x x 1 add def } for /y y 1 add def /x 0 def } for end } def } ifelse /tgifpatdict 10 dict def /tgifpatbyte { currentdict /retstr get exch pat i cellsz mod get put } def /tgifpatproc { 0 1 widthlim {tgifpatbyte} for retstr /i i 1 add def } def /tgifpatfill { tgifpatdict begin /h exch def /w exch def /lty exch def /ltx exch def /cellsz exch def /pat exch def /widthlim w cellsz div cvi 1 sub def /retstr widthlim 1 add string def /i 0 def ltx lty translate w h true [1 0 0 1 0 0] {tgifpatproc} imagemask ltx neg lty neg translate end } def /pat1 def /pat2 <0000000000000000> def /pat3 <8000000008000000> def /pat4 <8800000022000000> def /pat5 <8800220088002200> def /pat6 <8822882288228822> def /pat7 def /pat8 <77dd77dd77dd77dd> def /pat9 <77ffddff77ffddff> def /pat10 <77ffffff77ffffff> def /pat11 <7fffffff7fffffff> def /pat12 <8040200002040800> def /pat13 <40a00000040a0000> def /pat14 def /pat15 def /pat16 def /pat17 <038448300c020101> def /pat18 <081c22c180010204> def /pat19 <8080413e080814e3> def /pat20 <8040201008040201> def /pat21 <8844221188442211> def /pat22 <77bbddee77bbddee> def /pat23 def /pat24 <7fbfdfeff7fbfdfe> def /pat25 <3e1f8fc7e3f1f87c> def /pat26 <0102040810204080> def /pat27 <1122448811224488> def /pat28 def /pat29 <83070e1c3870e0c1> def /pat30 def /pat31 <7cf8f1e3c78f1f3e> def /tgifcentertext { dup stringwidth pop 2 div neg 0 rmoveto } def /tgifrighttext { dup stringwidth pop neg 0 rmoveto } def /tgifreencsmalldict 12 dict def /tgifReEncodeSmall { tgifreencsmalldict begin /newcodesandnames exch def /newfontname exch def /basefontname exch def /basefontdict basefontname findfont def /newfont basefontdict maxlength dict def basefontdict { exch dup /FID ne { dup /Encoding eq { exch dup length array copy newfont 3 1 roll put } { exch newfont 3 1 roll put } ifelse } { pop pop } ifelse } forall newfont /FontName newfontname put newcodesandnames aload pop newcodesandnames length 2 idiv { newfont /Encoding get 3 1 roll put} repeat newfontname newfont definefont pop end } def /tgifgray { 8 1 0 72 300 32 div div tgifsetpattern } bind def /tgifboxdict 6 dict def /tgifboxstroke { tgifboxdict begin /pat def /w def /y2 exch def /x2 exch def /y1 exch def /x1 exch def 1.415 setmiterlimit w 1 eq { w setlinewidth } if pat pat1 ne pat pat2 ne and { gsave pat tgifgray } if newpath x1 y1 moveto x2 y1 lineto x2 y2 lineto x1 y2 lineto closepath pat pat2 eq { 1 setgray stroke 0 setgray } { stroke } ifelse pat pat1 ne pat pat2 ne and { grestore } if w 1 eq { 1 setlinewidth } if 1 setmiterlimit end } def /tgifboxfill { tgifboxdict begin /pat def /y2 exch def /x2 exch def /y1 exch def /x1 exch def pat pat1 ne pat pat2 ne and { gsave pat tgifgray } if newpath x1 y1 moveto x2 y1 lineto x2 y2 lineto x1 y2 lineto closepath pat pat2 eq { 1 setgray fill 0 setgray } { fill } ifelse pat pat1 ne pat pat2 ne and { grestore } if end } def end %%PageBoundingBox: 15 680 305 764 tgifdict begin /tgifsavedpage save def 1 setmiterlimit 1 setlinewidth 0 setgray 72 0 mul 72 11.00 mul translate 72 128 div 100 mul 100 div dup neg scale gsave % POLY/OPEN-SPLINE gsave newpath 156 105 moveto 156 137 lineto stroke grestore % POLY/OPEN-SPLINE gsave newpath 171 125 moveto 0 56 atan dup cos 8 mul 227 exch sub exch sin 8 mul 125 exch sub lineto stroke grestore gsave newpath 227 125 8 3 56 0 tgifarrowtip closepath fill grestore % BOX gsave 1.415 setmiterlimit newpath 232 103 moveto 296 103 lineto 296 135 lineto 232 135 lineto closepath stroke 1 setmiterlimit grestore % POLY/OPEN-SPLINE gsave newpath 264 103 moveto 264 135 lineto stroke grestore % POLY/OPEN-SPLINE gsave newpath 279 117 moveto 0 59 atan dup cos 8 mul 338 exch sub exch sin 8 mul 117 exch sub lineto stroke grestore gsave newpath 338 117 8 3 59 0 tgifarrowtip closepath fill grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 289 172 moveto (a different piece of text) show grestore % POLY/OPEN-SPLINE gsave newpath 248 119 moveto 248 168 lineto 0 29 atan dup cos 8 mul 277 exch sub exch sin 8 mul 168 exch sub lineto stroke grestore gsave newpath 277 168 8 3 29 0 tgifarrowtip closepath fill grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 147 66 moveto (kill-ring-yank-pointer) show grestore % POLY/OPEN-SPLINE gsave newpath 207 76 moveto 207 114 lineto 0 18 atan dup cos 8 mul 225 exch sub exch sin 8 mul 114 exch sub lineto stroke grestore gsave newpath 225 114 8 3 18 0 tgifarrowtip closepath fill grestore % BOX gsave 1.415 setmiterlimit newpath 341 98 moveto 405 98 lineto 405 130 lineto 341 130 lineto closepath stroke 1 setmiterlimit grestore % POLY/OPEN-SPLINE gsave newpath 372 98 moveto 372 130 lineto stroke grestore % POLY/OPEN-SPLINE gsave newpath 388 115 moveto 0 48 atan dup cos 8 mul 436 exch sub exch sin 8 mul 115 exch sub lineto stroke grestore gsave newpath 436 115 8 3 48 0 tgifarrowtip closepath fill grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 448 121 moveto (nil) show grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 397 154 moveto (yet more text) show grestore % POLY/OPEN-SPLINE gsave newpath 356 112 moveto 356 149 lineto 0 35 atan dup cos 8 mul 391 exch sub exch sin 8 mul 149 exch sub lineto stroke grestore gsave newpath 391 149 8 3 35 0 tgifarrowtip closepath fill grestore % BOX gsave 1.415 setmiterlimit newpath 126 105 moveto 190 105 lineto 190 137 lineto 126 137 lineto closepath stroke 1 setmiterlimit grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 206 192 moveto (some text) show grestore % POLY/OPEN-SPLINE gsave newpath 142 120 moveto 142 187 lineto 0 48 atan dup cos 8 mul 190 exch sub exch sin 8 mul 187 exch sub lineto stroke grestore gsave newpath 190 187 8 3 48 0 tgifarrowtip closepath fill grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 32 66 moveto (kill-ring) show grestore % POLY/OPEN-SPLINE gsave newpath 65 81 moveto 65 121 lineto 0 51 atan dup cos 8 mul 116 exch sub exch sin 8 mul 121 exch sub lineto stroke grestore gsave newpath 116 121 8 3 51 0 tgifarrowtip closepath fill grestore grestore tgifsavedpage restore end %MatchingCreationDate: Wed Mar 8 14:27:28 1995 emacs-lisp-intro-1.04/emacs-lisp-intro.texi100644 12062 13 2437344 6034006753 17001 0ustar bobuser\input texinfo @c -*-texinfo-*- @comment %**start of header @setfilename emacs-lisp-intro.info @c sethtmlfilename emacs-lisp-intro.html @settitle Programming in Emacs Lisp @syncodeindex vr cp @syncodeindex fn cp @setchapternewpage odd @finalout @c --------- @c smallbook @c clear largebook @c set largebook @c set print-postscript-figures @clear print-postscript-figures @c --------- @comment %**end of header @c <<<< Now set for largebook, no Postscript figures >>>> @set edition-number 1.04 @set update-date 2 October 1995 @c ================ Included Figures ================ @c Set print-postscript-figures if you print PostScript figures. @c If you clear this, the ten figures will be printed as ASCII diagrams. @c (This is not relevant to Info, since Info only handles ASCII.) @c Your site may require editing changes to print PostScript; in this @c case, search for `print-postscript-figures' and make appropriate changes. @c ================ Size to Print Book ================ @c This manual can be printed in any of three different sizes. @c In the above header, set @-commands appropriately. @c 7 by 9.25 inches: @c @smallbook @c @clear largebook @c 8.5 by 11 inches: @c @set largebook @c European A4 size paper: @c @afourpaper @c @set largebook @c ================ How to Create an Info file ================ @c If you have `makeinfo' installed, run the following command @c (where % is the shell prompt): @c % makeinfo emacs-lisp-intro.texi @c or else, inside of GNU Emacs, find the `emacs-lisp-intro.texi' @c and then run: @c M-x texinfo-format-buffer @c After creating the Info file, edit your Info `dir' file @c appropriately. (The `dir' file is often in the `/usr/local/info/' @c directory; you can use the START-INFO-DIR-ENTRY information below.) @c ================ How to Create an HTML file ================ @c To convert to HTML format, apply `texi2html' or @c similar command to the `emacs-lisp-intro.texi' file. @c ================ How to Typeset and Print ================ @c Note: unless you change it, this file does not format with the @c obsolete `texinfo.tex 2.108'; use a more recent version. This file @c formats without error using `TeX 3.1415' and `texinfo.tex 2.145'. @c If you do not include PostScript figures, run either of the @c following command sequences, or similar commands suited to your @c system: @c % texi2dvi emacs-lisp-intro.texi @c % lpr -d emacs-lisp-intro.dvi @c or else: @c % tex emacs-lisp-intro.texi @c % texindex emacs-lisp-intro.?? @c % tex emacs-lisp-intro.texi @c % lpr -d emacs-lisp-intro.dvi @c If you include the PostScript figures, you must convert the .dvi @c file to a .ps file before printing. Run either of the @c following command sequences, or one similar: @c @c % dvips -f < emacs-lisp-intro.dvi > emacs-lisp-intro.ps @c @c or else: @c @c % postscript -p < emacs-lisp-intro.dvi > emacs-lisp-intro.ps @c @c (Note: if you edit the book so as to change the length of the @c table of contents, you may have to change the value of `pageno' below.) @c ================ End of Formatting Sections ================ @c For next or subsequent edition: @c create function using with-output-to-temp-buffer @c create a major mode, with keymaps @c run an asynchronous process, like grep or diff @c use colors and fonts in X @c For all sized formats: Experiment with smaller than normal amounts of @c whitespace between chapters, sections, and paragraphs. @tex \global\chapheadingskip = 15pt plus 4pt minus 2pt \global\secheadingskip = 12pt plus 3pt minus 2pt \global\subsecheadingskip = 9pt plus 2pt minus 2pt \global\parskip 2pt plus 1pt @end tex @c For 8.5 by 11 inch format: do not use such a small amount of @c whitespace between paragraphs as in experiment above: @ifset largebook @tex \global\parskip 6pt plus 1pt @end tex @end ifset @c For all sized formats: Experiment with printing within-book cross @c reference with ``...'' rather than [...] @tex % Need following so comma appears after section numbers. \global\def\Ysectionnumberandtype{% \ifnum\secno=0 \putwordChapter\xreftie\the\chapno, \space % \else \ifnum \subsecno=0 \putwordSection\xreftie\the\chapno.\the\secno, \space % \else \ifnum \subsubsecno=0 % \putwordSection\xreftie\the\chapno.\the\secno.\the\subsecno, \space % \else % \putwordSection\xreftie\the\chapno.\the\secno.\the\subsecno.\the\subsubsecno, \space% \fi \fi \fi } \global\def\Yappendixletterandtype{% \ifnum\secno=0 \putwordAppendix\xreftie'char\the\appendixno{}, \space% \else \ifnum \subsecno=0 \putwordSection\xreftie'char\the\appendixno.\the\secno, \space % \else \ifnum \subsubsecno=0 % \putwordSection\xreftie'char\the\appendixno.\the\secno.\the\subsecno, \space % \else % \putwordSection\xreftie'char\the\appendixno.\the\secno.\the\subsecno.\the\subsubsecno, \space % \fi \fi \fi } \global\def\xrefX[#1,#2,#3,#4,#5,#6]{\begingroup \def\printedmanual{\ignorespaces #5}% \def\printednodename{\ignorespaces #3}% \setbox1=\hbox{\printedmanual}% \setbox0=\hbox{\printednodename}% \ifdim \wd0 = 0pt % No printed node name was explicitly given. \ifx\SETxref-automatic-section-title\relax % % Use the actual chapter/section title appear inside % the square brackets. Use the real section title if we have it. \ifdim \wd1>0pt% % It is in another manual, so we don't have it. \def\printednodename{\ignorespaces #1}% \else \ifhavexrefs % We know the real title if we have the xref values. \def\printednodename{\refx{#1-title}}% \else % Otherwise just copy the Info node name. \def\printednodename{\ignorespaces #1}% \fi% \fi \def\printednodename{#1-title}% \else % Use the node name inside the square brackets. \def\printednodename{\ignorespaces #1}% \fi \fi % % If we use \unhbox0 and \unhbox1 to print the node names, TeX does not % insert empty discretionaries after hyphens, which means that it will % not find a line break at a hyphen in a node names. Since some manuals % are best written with fairly long node names, containing hyphens, this % is a loss. Therefore, we give the text of the node name again, so it % is as if TeX is seeing it for the first time. \ifdim \wd1 > 0pt \putwordsection{} ``\printednodename'' in \cite{\printedmanual}% \else % _ (for example) has to be the character _ for the purposes of the % control sequence corresponding to the node, but it has to expand % into the usual \leavevmode...\vrule stuff for purposes of % printing. So we \turnoffactive for the \refx-snt, back on for the % printing, back off for the \refx-pg. {\turnoffactive \refx{#1-snt}{}}% % \space [\printednodename],\space % <= original % \putwordsection{} ``\printednodename'',\space ``\printednodename'',\space \turnoffactive \putwordpage\tie\refx{#1-pg}{}% \fi \endgroup} @end tex @c ---------------------------------------------------- @ignore @ifinfo @format START-INFO-DIR-ENTRY * Programming in Emacs Lisp: (emacs-lisp-intro.info). A simple introduction. END-INFO-DIR-ENTRY @end format @end ifinfo @end ignore @ifinfo This is an introduction to @cite{Programming in Emacs Lisp}, for people who are not programmers. Edition @value{edition-number}, @value{update-date} Copyright (C) 1990, '91, '92, '93, '94, '95 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. @ignore Permission is granted to process this file through TeX and print the results, provided the printed document carries a copying permission notice identical to this one except for the removal of this paragraph (this paragraph not being relevant to the printed manual). @end ignore Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the sections entitled ``Copying'' and ``GNU General Public License'' are included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Free Software Foundation. @end ifinfo @c half title; two lines here, so do not use `shorttitlepage' @tex {\begingroup% \hbox{}\vskip 1.5in \chaprm \centerline{Programming in Emacs Lisp}% \endgroup}% {\begingroup\hbox{}\vskip 0.5in \chaprm \centerline{An Introduction}% \endgroup\page\hbox{}\page} @end tex @titlepage @title Programming in Emacs Lisp @subtitle An Introduction @subtitle Edition @value{edition-number}, @value{update-date} @author by Robert J. Chassell @page @vskip 0pt plus 1filll Copyright @copyright{} 1990, '91, '92, '93, '94, '95 Free Software Foundation, Inc. @sp 2 Published by the Free Software Foundation, Inc.@* 59 Temple Place, Suite 330@* Boston, MA 02111-1307 USA@* @c Printed copies are available for $20 each.@* ISBN-1882114-41-8 Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Free Software Foundation. @end titlepage @iftex @headings off @evenheading @thispage @| @| @thischapter @oddheading @thissection @| @| @thispage @end iftex @node Top, Preface, (dir), (dir) @ifinfo This master menu first lists each chapter and index; then it lists every node in every chapter. @end ifinfo @menu * Preface:: What to look for. * List Processing:: What is Lisp? * Practicing Evaluation:: Running several programs. * Writing Defuns:: How to write function definitions. * Buffer Walk Through:: Exploring a few buffer-related functions. * More Complex:: A few, even more complex functions. * Narrowing & Widening:: Restricting your and Emacs attention to a region. * car cdr & cons:: Fundamental functions in Lisp. * Cutting & Storing Text:: Removing text and saving it. * List Implementation:: How lists are implemented in the computer. * Yanking:: Pasting stored text. * Loops & Recursion:: How to repeat a process. * Regexp Search:: Regular expression searches. * Counting Words:: A review of repetition and regexps. * Words in a defun:: Counting words in a @code{defun}. * Readying a Graph:: A prototype graph printing function. * Emacs Initialization:: How to write a @file{.emacs} file. * Debugging:: How to run the Emacs Lisp debuggers. * Conclusion:: Now you have the basics. * the-the:: An appendix: how to find reduplicated words. * Kill Ring:: An appendix: how the kill ring works. * Full Graph:: How to create a graph with labelled axes. * Index:: * About the Author:: --- The Detailed Node Listing --- Preface * On Reading this Text:: Read, gain familiarity, pick up habits.... * Who You Are:: For whom this is written. * Lisp History:: * Note for Novices:: You can read this as a novice. * Thank You:: List Processing * Lisp Lists:: What are lists? * Run a Program:: Any list in Lisp is a program ready to run. * Making Errors:: Generating an error message. * Names & Definitions:: Names of symbols and function definitions. * Lisp Interpreter:: What the Lisp interpreter does. * Evaluation:: Running a program. * Variables:: Returning a value from a variable. * Arguments:: Passing information to a function. * set & setq:: Setting the value of a variable. * Summary:: The major points. * Error Message Exercises:: Lisp Lists * Lisp Atoms:: Elemental entities. * Whitespace in Lists:: Formating lists to be readable. * Typing Lists:: How GNU Emacs helps you type lists. The Lisp Interpreter * Byte Compiling:: Specially processing code for speed. Evaluation * Evaluating Inner Lists:: Lists within lists... Variables * Void Variable:: The error message for a symbol without a value. Arguments * Data types:: Types of data passed to a function. * Args as Variable or List:: An argument can be the value of a variable or list. * Variable Number of Arguments:: Some functions may take a variable number of arguments. * Wrong Type of Argument:: Passing an argument of the wrong type to a function. * message:: A useful function for sending messages. Setting the Value of a Variable * Using set:: Setting values. * Using setq:: Setting a quoted value. * Counting:: Using @code{setq} to count. Practicing Evaluation * How to Evaluate:: Typing editing commands or @kbd{C-x C-e} causes evaluation. * Buffer Names:: Buffers and files are different. * Getting Buffers:: Getting a buffer itself, not merely its name. * Switching Buffers:: How to change to another buffer. * Buffer Size & Locations:: Where point is located and the size of the buffer. * Evaluation Exercise:: How To Write Function Definitions * Primitive Functions:: Some functions are written in C. * defun:: The @code{defun} special form. * Install:: Install a Function Definition. * Interactive:: Making a function interactive. * Interactive Options:: Different options for @code{interactive}. * Permanent Installation:: Installing code permanently. * let:: Creating and initializing local variables. * if:: What if? * else:: If--then--else expressions. * Truth & Falsehood:: What Lisp considers false and true. * save-excursion:: Keeping track of point, mark, and buffer. * Review:: * defun Exercises:: Install a Function Definition * Change a defun:: How to change a function definition. Make a Function Interactive * multiply-by-seven in detail:: The interactive version. @code{let} * Parts of let Expression:: * Sample let Expression:: * Uninitialized let Variables:: The @code{if} Special Form * type-of-animal in detail:: An example of an @code{if} expression. @code{save-excursion} * Template for save-excursion:: One slot to fill in. A Few Buffer--Related Functions * Finding More:: How to find more information. * simplified-beginning-of-buffer:: Shows @code{goto-char}, @code{point-min}, and @code{push-mark}. * mark-whole-buffer:: Almost the same as @code{beginning-of-buffer}. * append-to-buffer:: Uses @code{save-excursion} and @code{insert-buffer-substring}. * Buffer Related Review:: Review. * Buffer Exercises:: The Definition of @code{mark-whole-buffer} * Body of mark-whole-buffer:: Only three lines of code. The Definition of @code{append-to-buffer} * append interactive:: A two part interactive expression. * append-to-buffer body:: Incorporates a @code{let} expression. * append save-excursion:: How the @code{save-excursion} works. A Few More Complex Functions * copy-to-buffer:: With @code{set-buffer}, @code{get-buffer-create}. * insert-buffer:: Read-only, and with @code{or}. * beginning-of-buffer:: Shows @code{goto-char}, @code{point-min}, and @code{push-mark}. * Second Buffer Related Review:: * &optional Exercise :: The Definition of @code{insert-buffer} * insert interactive expression:: A read-only situation. * insert-buffer body:: The body has an @code{or} and a @code{ let}. * if & or:: Using an @code{if} instead of an @code{or}. * insert or:: How the @code{or} expression works. * insert let:: Two @code{save-excursion} expressions. The Interactive Expression in @code{insert-buffer} * read-only buffer:: * @samp{b} for interactive:: Complete Definition of @code{beginning-of-buffer} * Optional Arguments:: * beginning-of-buffer opt arg:: Example with optional argument. * beginning-of-buffer complete:: @code{beginning-of-buffer} with an Argument * large-case:: Division and multiplication in a large buffer. * small-case:: Functions embedded in parentheses. Narrowing and Widening * narrowing advantages:: The Advantages of Narrowing * save-restriction:: The @code{save-restriction} special form. * what-line:: The number of the line that point is on. * narrow Exercise:: @code{car}, @code{cdr}, @code{cons}: Fundamental Functions * Strange Names:: An historical aside: why the strange names? * car & cdr:: Functions for extracting part of a list. * cons:: Constructing a list. * nthcdr:: Calling @code{cdr} repeatedly. * setcar:: Changing the first element of a list. * setcdr:: Changing the rest of a list. * cons Exercise:: @code{cons} * length:: How to find the length of a list. Cutting and Storing Text * Storing Text:: Text is stored in a list. * zap-to-char:: Cutting out text up to a character. * kill-region:: Cutting text out of a region. * delete-region:: A digression into C. * defvar:: How to give a variable an initial value. * copy-region-as-kill:: A definition for copying text. * cons & search-fwd Review:: * search Exercises:: @code{zap-to-char} * zap-to-char interactive:: A three part interactive expression. * zap-to-char body:: A short overview. * search-forward:: How to search for a string. * progn:: The @code{progn} function. * Summing up zap-to-char:: Using @code{point} and @code{search-forward}. * v-18-zap-to-char:: The version 18 implementation. The Version 18 Implementation * progn body:: The body of the @code{progn} expression @code{copy-region-as-kill} * copy-region-as-kill body:: The body of @code{copy-region-as-kill} The Body of @code{copy-region-as-kill} * kill-append function:: The @code{kill-append} function * copy-region-as-kill else-part:: The else-part of @code{copy-region-as-kill} How Lists are Implemented * List Exercise:: Yanking Text Back * Kill Ring Overview:: The kill ring is a list. * kill-ring-yank-pointer:: The @code{kill-ring-yank-pointer} variable. * yank nthcdr Exercises:: Loops and Recursion * while:: Causing a stretch of code to repeat. * Recursion:: Causing a function to call itself. * Looping exercise:: @code{while} * Loop Example:: A @code{while} loop that uses a list. * print-elements-of-list:: Uses @code{while}, @code{car}, @code{cdr}. * Incrementing Loop:: A loop with an incrementing counter. * Decrementing Loop:: A loop with a decrementing counter. A Loop with an Incrementing Counter * Incrementing Example:: Counting pebbles in a triangle. * Inc Example parts:: The parts of the function definition. * Inc Example altogether:: Putting the function definition together. Loop with a Decrementing Counter * Decrementing Example:: More pebbles on the beach. * Dec Example parts:: The parts of the function definition. * Dec Example altogether:: Putting the function definition together. Recursion * Recursion with list:: Using a list as the test whether to recurse. * Recursive triangle function:: Replacing a @code{while} loop with recursion. * Recursion with cond:: Recursion example with a different conditional. Recursion in Place of a Counter * Recursive Example arg of 3:: Regular Expression Searches * sentence-end:: The regular expression for @code{sentence-end}. * re-search-forward:: Very similar to @code{search-forward}. * forward-sentence:: A straightforward example of regexp search. * forward-paragraph:: A somewhat complex example. * etags:: How to create your own @file{TAGS} table. * Regexp Review:: * re-search Exercises:: @code{forward-sentence} * fwd-sentence while loops:: Two @code{while} loops. * fwd-sentence re-search:: A regular expression search. @code{forward-paragraph}: a Goldmine of Functions * fwd-para let:: The @code{let*} expression. * fwd-para while:: The forward motion @code{while} loop. * fwd-para between paragraphs:: Movement between paragraphs. * fwd-para within paragraph:: Movement within paragraphs. * fwd-para no fill prefix:: When there is no fill prefix. * fwd-para with fill prefix:: When there is a fill prefix. * fwd-para summary:: Summary of @code{forward-paragraph} code. Counting: Repetition and Regexps * Why Count Words:: Emacs lacks a word count command. * count-words-region:: Use a regexp, but find a problem. * recursive-count-words:: Start with case of no words in region. * Counting Exercise:: The @code{count-words-region} Function * Whitespace Bug:: The Whitespace Bug in @code{count-words-region} Counting Words in a @code{defun} * Divide and Conquer:: Split a daunting project into parts. * Words and Symbols:: What to count? * Syntax:: What constitutes a word or symbol? * count-words-in-defun:: Very like @code{count-words}. * Several defuns:: Counting several defuns in a file. * Find a File:: Do you want to look at a file? * lengths-list-file:: A list of the lengths of many definitions. * Several files:: Counting in definitions in different files. * Several files recursively:: Recursively counting in different files. * Prepare the data:: Prepare the data for display in a graph. Count Words in @code{defuns} in Different Files * append:: Attaching one list to another. Prepare the Data for Display in a Graph * Sorting:: Sorting lists. * Files List:: Making a list of files. Readying a Graph * Columns of a graph:: How to print individual columns. * graph-body-print:: How to print the body of a graph. * recursive-graph-body-print:: * Printed Axes:: * Line Graph Exercise:: Your @file{.emacs} File * Default Configuration:: Emacs has sensible defaults. * Site-wide Init:: You can write site-wide init files. * edit-options:: How to set some variables for a session. * Beginning a .emacs File:: How to write a @code{.emacs file}. * Text and Auto-fill:: Automatically wrap lines. * Mail Aliases:: Use abbreviations for email addresses. * Indent Tabs Mode:: Don't use tabs with @TeX{} * Keybindings:: Create some personal keybindings. * Loading Files:: Load (i.e.@: evaluate) files automatically. * Autoload:: Make functions available. * Simple Extension:: Define a function; bind it to a key. * Keymaps:: More about key binding. * X11 Colors:: Colors in version 19 in X. * V19 Miscellaneous:: Automatically resize minibuffer, and more. * Mode Line:: How to customize your mode line. Debugging * debug:: How to use the built-in debugger. * debug-on-entry:: Start debugging when you call a function. * debug-on-quit:: Start debugging when you quit with @kbd{C-g}. * edebug:: How to use Edebug, a source level debugger. * Debugging Exercises:: Handling the Kill Ring * rotate-yank-pointer:: Move a pointer along a list and around. * yank:: Paste a copy of a clipped element. * yank-pop:: Insert first element pointed to. The @code{rotate-yank-pointer} Function * rotate-yk-ptr body:: The Body of @code{rotate-yank-pointer}. The Body of @code{rotate-yank-pointer} * rotate-yk-ptr else-part:: The else-part of the @code{if} expression. * Remainder Function:: The remainder, @code{%}, function. * rotate-yk-ptr remainder:: Using @code{%} in @code{rotate-yank-pointer}. * kill-rng-yk-ptr last elt:: Pointing to the last element. @code{yank} * rotate-yk-ptr arg:: Pass the argument to @code{rotate-yank-pointer}. * rotate-yk-ptr negative arg:: Pass a negative argument. A Graph with Labelled Axes * Labelled Example:: How a finished graph should look. * print-graph Varlist:: @code{let} expression in @code{print-graph}. * print-Y-axis:: Print a label for the vertical axis. * print-X-axis:: Print a horizontal label. * Print Whole Graph:: The function to print a complete graph. The @code{print-Y-axis} Function * Compute a Remainder:: How to compute the remainder of a division. * Y Axis Element:: Construct a line for the Y axis. * Y-axis-column:: Generate a list of Y axis labels. * print-Y-axis Final:: Print a vertical axis, final version. The @code{print-X-axis} Function * X Axis Tic Marks:: Create tic marks for the horizontal axis. Printing the Whole Graph * Test print-graph:: Run a short test. * Graphing words in defuns:: Executing the final code. * Final Printed Graph:: The graph itself! Graphing Numbers of Words and Symbols * lambda:: How to write an anonymous function. * mapcar:: Apply a function to elements of a list. * Another Bug:: Yet another @dots{} of a most insidious type. @end menu @c >>>> Set pageno appropriately <<<< @c The first page of the Preface is a roman numeral; it is the first @c right handed page after the Table of Contents; hence the following @c setting must be for an odd negative number. @iftex @pageno = -9 @end iftex @node Preface, List Processing, Top, Top @comment node-name, next, previous, up @unnumbered Preface Most of the GNU Emacs text editor is written in the programming language called Emacs Lisp. The code written in this programming language is the software---the sets of instructions---that tell the computer what to do when you give it commands. Emacs is designed so that you can write new code in Emacs Lisp and easily install it as an extension to the editor. This is why Emacs is called the ``extensible editor''. (Indeed, since Emacs does so much more than provide editing capabilities, it should perhaps be called an ``extensible computing environment'', but that phrase is quite a mouthful. Also, everything you do in Emacs---find the Mayan date and phases of the moon, simplify polynomials, debug code, manage files, read letters, write books---all these activities are kinds of editing in the most general sense of the word.) Although Emacs Lisp is usually thought of in association with the text editor, it is a full computer programming language. You can use it as you would any other programming language. Perhaps you want to understand programming; perhaps you want to extend Emacs; or perhaps you want to become a programmer. This introduction to Emacs Lisp is designed to get you started: to guide you in learning the fundamentals of programming, and more importantly, to show you how you can teach yourself to go further. @menu * On Reading this Text:: Read, gain familiarity, pick up habits.... * Who You Are:: For whom this is written. * Lisp History:: * Note for Novices:: You can read this as a novice. * Thank You:: @end menu @node On Reading this Text, Who You Are, Preface, Preface @ifinfo @heading On Reading this Text @end ifinfo All through this document, you will see little sample programs you can run inside of Emacs. If you read this document in Info inside of GNU Emacs, you can run the programs as they appear. (This is easy to do and is explained when the examples are presented.) Alternatively, you can read this introduction as a printed book while sitting beside a computer running Emacs. (This is what I like to do; I like printed books.) If you don't have a running Emacs beside you, you can still read this book, but in this case, it is best to treat it as a novel or as a travel guide to a country not yet visited: interesting, but not the same as being there. Much of this introduction is dedicated to walk-throughs or guided tours of code used in GNU Emacs. These tours are designed for two purposes: first, to give you familiarity with real, working code (code you use every day); and, second, to give you familiarity with the way Emacs works. It is interesting to see how an editor is implemented. Also, I hope that you will pick up the habit of browsing through source code. You can learn from it and mine it for ideas. Having GNU Emacs is like having a dragon's cave of treasures. In addition to learning about Emacs as an editor and Emacs Lisp as a programming language, the examples and guided tours will give you an opportunity to get acquainted with Emacs as a Lisp programming environment. GNU Emacs supports programming and provides tools that you will want to become comfortable using, such as @kbd{M-.} (the key which invokes the @code{find-tag} command). You will also learn about buffers and other objects that are part of the editing environment. Learning about these features of Emacs is like learning new routes around your home town. @ignore In addition, I have written several programs as extended examples. Although these are examples, the programs are real. I use them. Other people use them. You may use them. Beyond the fragments of programs used for illustrations, there is very little in here that is `just for teaching purposes'; what you see is used. This is a great advantage of Emacs Lisp: it is easy to learn to use it for work. @end ignore Finally, I hope to convey some of the skills for using Emacs to learn aspects of programming that you don't know. You can often use Emacs to help you understand what puzzles you or to find out how to do something new. This self-reliance is not only a pleasure, but an advantage. @node Who You Are, Lisp History, On Reading this Text, Preface @comment node-name, next, previous, up @unnumberedsec For Whom This is Written This text is written as an elementary introduction for people who are not programmers. If you are a programmer, you may not be satisfied with this primer. The reason is that you may have become expert at reading reference manuals and be put off by the way this text is organized. An expert programmer who reviewed this text said to me: @quotation @i{I prefer to learn from reference manuals. I ``dive into'' each paragraph, and ``come up for air'' between paragraphs.} @i{When I get to the end of a paragraph, I assume that that subject is done, finished, that I know everything I need (with the possible exception of the case when the next paragraph starts talking about it in more detail). I expect that a well written reference manual will not have a lot of redundancy, and that it will have excellent pointers to the (one) place where the information I want is.} @end quotation This introduction is not written for this person! Firstly, I try to say everything at least three times: first, to introduce it; second, to show it in context; and third, to show it in a different context, or to review it. Secondly, I hardly ever put all the information about a subject in one place, much less in one paragraph. To my way of thinking, that imposes too heavy a burden on the reader. Instead I try to explain only what you need to know at the time. (Sometimes I include a little extra information so you won't be surprised later when the additional information is formally introduced.) When you read this text, you are not expected to learn everything the first time. Frequently, you need only make, as it were, a `nodding acquaintance' with some of the items mentioned. My hope is that I have structured the text and given you enough hints that you will be alert to what is important, and concentrate on it. You will need to ``dive into'' some paragraphs; there is no other way to read them. But I have tried to keep down the number of such paragraphs. This book is intended as an approachable hill, rather than as a daunting mountain. This @emph{introduction} to @cite{Programming in Emacs Lisp} has a companion document, @iftex @cite{The GNU Emacs Lisp Reference Manual}. @end iftex @ifinfo @ref{Top, , The GNU Emacs Lisp Reference Manual, elisp, The GNU Emacs Lisp Reference Manual}. @end ifinfo The reference manual has more detail than this introduction. In the reference manual, all the information about one topic is concentrated in one place. You should turn to it if you are like the programmer quoted above. And, of course, after you have read this @cite{Introduction}, you will find the @cite{Reference Manual} useful when you are writing your own programs. @node Lisp History, Note for Novices, Who You Are, Preface @unnumberedsec Lisp History @cindex Lisp history Lisp was first developed in the late 1950s at the Massachusetts Institute of Technology for research in artificial intelligence. The great power of the Lisp language makes it superior for other purposes as well, such as writing editor commands. @cindex Maclisp @cindex Common Lisp GNU Emacs Lisp is largely inspired by Maclisp, which was written at MIT in the 1960's. It is somewhat inspired by Common Lisp, which became a standard in the 1980s. However, Emacs Lisp is much simpler than Common Lisp. (The standard Emacs distribution contains an optional extensions file, @file{cl.el}, that adds many Common Lisp features to Emacs Lisp.) @node Note for Novices, Thank You, Lisp History, Preface @comment node-name, next, previous, up @unnumberedsec A Note for Novices If you don't know GNU Emacs, you can still read this document profitably. However, I recommend you learn Emacs, if only to learn to move around your computer screen. You can teach yourself how to use Emacs with the on-line tutorial. To use it, type @kbd{C-h t}. (This means you press and release the @key{CTRL} key and the @kbd{h} at the same time, and then press and release @kbd{t}.) Also, I often refer to one of Emacs's standard commands by listing the keys which you press to invoke the command and then giving the name of the command in parentheses, like this: @kbd{M-C-\} (@code{indent-region}). What this means is that the @code{indent-region} command is customarily invoked by typing @kbd{M-C-\}. (You can, if you wish, change the keys that are typed to invoke the command; this is called @dfn{rebinding}. @xref{Keymaps, , Keymaps}.) The abbreviation @kbd{M-C-\} means that you type your @key{META} key, @key{CTRL} key and @key{\} key all at the same time. Sometimes a combination like this is called a keychord, since it is similar to the way you play a chord on a piano. If your keyboard does not have a @key{META} key, the @key{ESC} key prefix is used in place of it. In this case, @kbd{M-C-\} means that you press and release your @key{ESC} key and then type the @key{CTRL} key and the @key{\} key at the same time. If you are reading this in Info using GNU Emacs, you can read through this whole document just by pressing the space bar, @key{SPC}. (To learn about Info, type @kbd{C-h i} and then select Info.) A note on terminology: when I use the word Lisp alone, I am usually referring to the various dialects of Lisp in general, but when I speak of Emacs Lisp, I am referring to GNU Emacs Lisp in particular. @node Thank You, , Note for Novices, Preface @comment node-name, next, previous, up @unnumberedsec Thank You My thanks to all who helped me with this book. My especial thanks to @r{Jim Blandy}, @r{Noah Friedman}, @w{Jim Kingdon}, @r{Roland McGrath}, @w{Frank Ritter}, @w{Randy Smith}, @w{Richard M.@: Stallman}, and @w{Melissa Weisshaus}. My thanks also go to both @w{Philip Johnson} and @w{David Stampe} for their patient encouragement. My mistakes are my own. @c ================ Beginning of main text ================ @c Start main text on right-hand (verso) page @tex \par\vfill\supereject \headings off \ifodd\pageno \par\vfill\supereject \else \par\vfill\supereject \page\hbox{}\page \par\vfill\supereject \fi @end tex @iftex @headings off @evenheading @thispage @| @| @thischapter @oddheading @thissection @| @| @thispage @pageno = 1 @end iftex @node List Processing, Practicing Evaluation, Preface, Top @comment node-name, next, previous, up @chapter List Processing To the untutored eye, Lisp is a strange programming language. In Lisp code there are parentheses everywhere. Some people even claim that the name stands for `Lots of Isolated Silly Parentheses'. But the claim is unwarranted. Lisp stands for LISt Processing and the programming language handles @emph{lists} (and lists of lists) by putting them between parentheses. The parentheses mark the boundaries of the list. Sometimes a list is preceded by a single apostrophe or quotation mark, @samp{'}. Lists are the basis of Lisp. @menu * Lisp Lists:: What are lists? * Run a Program:: Any list in Lisp is a program ready to run. * Making Errors:: Generating an error message. * Names & Definitions:: Names of symbols and function definitions. * Lisp Interpreter:: What the Lisp interpreter does. * Evaluation:: Running a program. * Variables:: Returning a value from a variable. * Arguments:: Passing information to a function. * set & setq:: Setting the value of a variable. * Summary:: The major points. * Error Message Exercises:: @end menu @node Lisp Lists, Run a Program, List Processing, List Processing @comment node-name, next, previous, up @section Lisp Lists @cindex Lisp Lists In Lisp, a list looks like this: @code{'(rose violet daisy buttercup)}. This list is preceded by a single apostrophe. It could just as well be written as follows, which looks more like the kind of list you are likely to be familiar with: @example @group '(rose violet daisy buttercup) @end group @end example @noindent The elements of this list are the names of the four different flowers, separated from each other by whitespace and surrounded by parentheses, like flowers in a field with a stone wall around them. @cindex Flowers in a field Lists can also have numbers in them, as in this list: @code{(+ 2 2)}. This list has a plus-sign, @samp{+}, followed by two @samp{2}s, each separated by whitespace. In Lisp, both data and programs are represented the same way; that is, they are both lists of words, numbers, or other lists, separated by whitespace and surrounded by parentheses. (Since a program looks like data, one program may easily serve as data for another; this is a very powerful feature of Lisp.) (Incidentally, these two parenthetical remarks are @emph{not} Lisp lists, because they contain @samp{;} and @samp{.} as punctuation marks.) Here is another list, this time with a list inside of it: @example '(this list has (a list inside of it)) @end example The components of this list are the words @samp{this}, @samp{list}, @samp{has}, and the list @samp{(a list inside of it)}. The interior list is made up of the words @samp{a}, @samp{list}, @samp{inside}, @samp{of}, @samp{it}. @menu * Lisp Atoms:: Elemental entities. * Whitespace in Lists:: Formating lists to be readable. * Typing Lists:: How GNU Emacs helps you type lists. @end menu @node Lisp Atoms, Whitespace in Lists, Lisp Lists, Lisp Lists @comment node-name, next, previous, up @subsection Lisp Atoms @cindex Lisp Atoms In Lisp, what we have been calling words are called @dfn{atoms}. This term comes from the historical meaning of the word atom, which means `indivisible'. As far as Lisp is concerned, the words we have been using in the lists cannot be divided into any smaller parts and still mean the same thing as part of a program; likewise with numbers and single character symbols like @samp{+}. On the other hand, unlike an atom, a list can be split into parts. (@xref{car cdr & cons, , @code{car} @code{cdr} & @code{cons} Fundamental Functions}.) In a list, atoms are separated from each other by whitespace. They can be right next to a parenthesis. @cindex @samp{empty list} defined Technically speaking, a list in Lisp consists of parentheses surrounding atoms separated by whitespace or surrounding other lists or surrounding both atoms and other lists. A list can have just one atom in it or have nothing in it at all. A list with nothing in it looks like this: @code{()}, and is called the @dfn{empty list}. Unlike anything else, an empty list is considered both an atom and a list at the same time. @cindex Symbolic expressions, introduced @cindex @samp{expression} defined @cindex @samp{form} defined The printed representation of both atoms and lists are called @dfn{symbolic expressions} or, more concisely, @dfn{s-expressions}. The word @dfn{expression} by itself can refer to either the printed representation, or to the atom or list as it is held internally in the computer. Often, people use the term @dfn{expression} indiscriminately. (Also, in many texts, the word @dfn{form} is used as a synonym for expression.) Incidentally, the atoms that make up our universe were named such when they were thought to be indivisible; but it has been found that physical atoms are not indivisible. Parts can split off an atom or it can fission into two parts of roughly equal size. Physical atoms were named prematurely, before their truer nature was found. In Lisp, certain kinds of atom, such as an array, can be separated into parts; but the mechanism for doing this is different from the mechanism for splitting a list. As far as list operations are concerned, the atoms of a list are unsplittable. As in English, the meanings of the component letters of a Lisp atom are different from the meaning the letters make as a word. For example, the word for the South American sloth, the @samp{ai}, is completely different from the two words, @samp{a}, and @samp{i}. There are many kinds of atom in nature but only a few in Lisp: for example, @dfn{numbers}, such as 37, 511, or 1729, and @dfn{symbols}, such as @samp{+}, @samp{foo}, or @samp{forward-line}. The words we have listed in the examples above are all symbols. In everyday Lisp conversation, the word ``atom'' is not often used, because programmers usually try to be more specific about what kind of atom they are dealing with. Lisp programming is mostly about symbols (and sometimes numbers) within lists. (Incidentally, the preceding three word parenthetical remark is a proper list in Lisp, since it consists of atoms, which in this case are symbols, separated by whitespace and enclosed by parentheses, without any non-Lisp punctuation.) In addition, text between double quotation marks---even sentences or paragraphs---is an atom. Here is an example: @cindex Text between double quotation marks @example '(this list includes "text between quotation marks.") @end example @cindex @samp{string} defined @noindent In Lisp, all of the quoted text including the punctuation mark and the blank spaces is a single atom. This kind of atom is called a @dfn{string} (for `string of characters') and is the sort of thing that is used for messages that a computer can print for a human to read. Strings are a different kind of atom than numbers or symbols and are used differently. @node Whitespace in Lists, Typing Lists, Lisp Atoms, Lisp Lists @comment node-name, next, previous, up @subsection Whitespace in Lists @cindex Whitespace in lists The amount of whitespace in a list does not matter. From the point of view of the Lisp language, @example @group '(this list looks like this) @end group @end example @noindent is exactly the same as this: @example '(this list looks like this) @end example Both examples show what to Lisp is the same list, the list made up of the symbols @samp{this}, @samp{list}, @samp{looks}, @samp{like}, and @samp{this} in that order. Extra whitespace and newlines are designed to make a list more readable by humans. When Lisp reads the expression, it gets rid of all the extra whitespace (but it needs to have at least one space between atoms in order to tell them apart.) Odd as it seems, the examples we have seen cover almost all of what Lisp lists look like! Every other list in Lisp looks more or less like one of these examples, except that the list may be longer and more complex. In brief, a list is between parentheses, a string is between quotation marks, a symbol looks like a word, and a number looks like a number. (For certain situations, square brackets, dots and a few other special characters may be used; however, we will go quite far without them.) @node Typing Lists, , Whitespace in Lists, Lisp Lists @comment node-name, next, previous, up @subsection GNU Emacs Helps You Type Lists @cindex Help typing lists @cindex Formatting help If you type a Lisp expression in GNU Emacs using either Lisp Interaction mode or Emacs Lisp mode, you will have available to you several commands to format the Lisp expression so it is easy to read. For example, pressing the @key{TAB} key automatically indents the line the cursor is on by the right amount. A command to properly indent the code in a region is customarily bound to @kbd{M-C-\}. Indentation is designed so that you can see which elements of a list belongs to which list---elements of a sub-list are indented more than the elements of the enclosing list. In addition, when you type a closing parenthesis, Emacs momentarily jumps the cursor back to the matching opening parenthesis, so you can see which one it is. This is very useful, since every list you type in Lisp must have its closing parenthesis match its opening parenthesis. (@xref{Major Modes, , Major Modes, emacs, The GNU Emacs Manual}, for more information about Emacs' modes.) @node Run a Program, Making Errors, Lisp Lists, List Processing @comment node-name, next, previous, up @section Run a Program @cindex Run a program @cindex Program, running one @cindex @samp{evaluate} defined A list in Lisp---any list---is a program ready to run. If you run it (for which the Lisp jargon is @dfn{evaluate}), the computer will do one of three things: do nothing except return to you the list itself; send you an error message; or, treat the first symbol in the list as a command to do something. (Usually, of course, it is the last of these three things that you really want!) @c use code for the single apostrophe, not samp. The single apostrophe, @code{'}, that I put in front of some of the example lists in preceding sections is called a @dfn{quote}; when it precedes a list, it tells Lisp to do nothing with the list, other than take it as it is written. But if there is no quote preceding a list, the first item of the list is special: it is a command for the computer to obey. (In Lisp, these commands are called @emph{functions}.) The list @code{(+ 2 2)} shown above did not have a quote in front of it, so Lisp understands that the @code{+} is an instruction to do something with the rest of the list; in this case, to add the numbers that follow. If you are reading this inside of GNU Emacs in Info, here is how you can evaluate such a list: place your cursor immediately after the right hand parenthesis of the following list and then type @kbd{C-x C-e}: @example (+ 2 2) @end example @c use code for the number four, not samp. @noindent You will see the number @code{4} appear in the echo area. (In the jargon, what you have just done is ``evaluate the list.'' The echo area is the line at the bottom of the screen that displays or ``echoes'' text.) Now try the same thing with a quoted list: place the cursor right after the following list and type @kbd{C-x C-e}: @example '(this is a quoted list) @end example @noindent In this case, you will see @code{(this is a quoted list)} appear in the echo area. @cindex Lisp interpreter, explained @cindex Interpreter, Lisp, explained In both cases, what you are doing is giving a command to the program inside of GNU Emacs called the @dfn{Lisp interpreter}---giving the interpreter a command to evaluate the expression. The name of the Lisp interpreter comes from the word for the task done by a human who comes up with the meaning of an expression---who ``interprets'' it. You can also evaluate an atom that is not part of a list---one that is not surrounded by parentheses; again, the Lisp interpreter translates from the humanly readable expression to the language of the computer. But before discussing this (@pxref{Variables}), we will discuss what the Lisp interpreter does when you make an error. @node Making Errors, Names & Definitions, Run a Program, List Processing @comment node-name, next, previous, up @section Generate an Error Message @cindex Generate an error message @cindex Error message generation Partly so you won't worry if you do it accidentally, we will now give a command to the Lisp interpreter that generates an error message. This is a harmless activity; and indeed, we will often try to generate error messages intentionally. Once you understand the jargon, error messages can be informative. Instead of being called ``error'' messages, they should be called ``help'' messages. They are like signposts to a traveller in a strange country; decyphering them can be hard, but once understood, they can point the way. What we will do is evaluate a list that is not quoted and does not have a meaningful command as its first element. Here is a list almost exactly the same as the one we just used, but without the single-quote in front of it. Position the cursor right after it and type @kbd{C-x C-e}: @example (this is an unquoted list) @end example @noindent This time, you will see the following appear in the echo area: @example Symbol's function definition is void:@: this @end example @noindent (Also, your terminal may beep at you---some do, some don't; and others blink. This is just a device to get your attention.) The message goes away as soon as you type another key, even just to move the cursor. @cindex @samp{function} defined Based on what we already know, we can almost read this error message. We know the meaning of the word @samp{Symbol}. In this case, it refers to the first atom of the list, the word @samp{this}. The word @samp{function} was mentioned once before. It is a very important word. For our purposes, we can define it by saying that a @dfn{function} is a set of instructions to the computer that tell the computer to do something. (Technically, the symbol tells the computer where to find the instructions, but this is a complication we can ignore for the moment.) Now we can begin to understand the error message: @samp{Symbol's function definition is void:@: this}. The symbol (that is, the word @samp{this}) does not have a definition of any set of instructions for the computer to carry out. The slightly odd wording of the message, @samp{function definition is void}, is designed to cover the way Emacs Lisp is implemented, which is that when the symbol does not have a function definition attached to it, the place that should contains the instructions is `void'. On the other hand, since we were able to add 2 plus 2 successfully, by evaluating @code{(+ 2 2)}, we can infer that the symbol @code{+} must have a set of instructions for the computer to obey and those instructions must be to add the numbers that follow the @code{+}. @node Names & Definitions, Lisp Interpreter, Making Errors, List Processing @comment node-name, next, previous, up @section Symbol Names and Function Definitions @cindex Symbol names We can articulate another characteristic of Lisp based on what we have discussed so far---an important characteristic: a symbol, like @code{+}, is not itself the set of instructions for the computer to carry out. Instead, the symbol is used, perhaps temporarily, as a way of locating the definition or set of instructions. What we see is the name through which the instructions can be found. Names of people work the same way. I can be referred to as @samp{Bob}; however, I am not the letters @samp{B}, @samp{o}, @samp{b} but am the consciousness consistently associated with a particular life-form. The name is not me, but it can be used to refer to me. In Lisp, one set of instructions can be attached to several names. For example, the computer instructions for adding numbers can be linked to the symbol @code{plus} as well as to the symbol @code{+} (and are in some dialects of Lisp). Among humans, I can be referred to as @samp{Robert} as well as @samp{Bob} and by other words as well. On the other hand, a symbol can have only one function definition attached to it at a time. Otherwise, the computer would be confused as to which definition to use. If this were the case among people, only one person in the world could be named @samp{Bob}. However, the function definition to which the name refers can be changed readily. (@xref{Install, , Install a Function Definition}.) Since Emacs Lisp is large, it is customary to name symbols in a way that identifies the part of Emacs to which the function belongs. Thus, all the names for functions that deal with Texinfo start with @samp{texinfo-} and those for functions that deal with reading mail start with @samp{rmail-}. @node Lisp Interpreter, Evaluation, Names & Definitions, List Processing @comment node-name, next, previous, up @section The Lisp Interpreter @cindex Lisp interpreter, what it does @cindex Interpreter, what it does Based on what we have seen, we can now start to figure out what the Lisp interpreter does when we command it to evaluate a list. First, it looks to see whether there is a quote before the list; if there is, the interpreter just gives us the list. On the other hand, if there is no quote, the interpreter looks at the first element in the list and sees whether it has a function definition. If it does, the interpreter carries out the instructions in the function definition. Otherwise, the interpreter prints an error message. This is how Lisp works. Simple. There are added complications which we will get to in a minute, but these are the fundamentals. Of course, to write Lisp programs, you need to know how to write function definitions and attach them to names, and how to do this without confusing either yourself or the computer. Now, for the first complication. In addition to lists, the Lisp interpreter can evaluate a symbol that is not quoted and does not have parentheses around it. In this case, the Lisp interpreter will attempt to determine the symbol's value as a @dfn{variable}. This situation is described in the section on variables. (@xref{Variables}.) @cindex Special form The second complication occurs because some functions are unusual and do not work in the usual manner. Those that don't are called @dfn{special forms}. They are used for special jobs, like defining a function, and there are not many of them. In the next few chapters, you will be introduced to several of the more important special forms. The third and final complication is this: if the function that the Lisp interpreter is looking at is not a special form, and if it is part of a list, the Lisp interpreter looks to see whether the list has a list inside of it. If there is an inner list, the Lisp interpreter first figures out what it should do with the inside list, and then it works on the outside list. If there is yet another list embedded inside the inner list, it works on that one first, and so on. It always works on the innermost list first. The interpreter works on the innermost list first in order to find out the result of doing that. The result may be used by the enclosing expression. Otherwise, the interpreter works left to right, from one expression to the next. @menu * Byte Compiling:: Specially processing code for speed. @end menu @node Byte Compiling, , Lisp Interpreter, Lisp Interpreter @subsection Byte Compiling @cindex Byte compiling One other aspect of interpreting: the Lisp interpreter is able to interpret two kinds of entity: humanly readable code, on which we will focus exclusively, and specially processed code, called @dfn{byte compiled} code, which is not humanly readable. Byte compiled code runs faster than humanly readable code. You can transform humanly readable code into byte compiled code by running one of the compile commands such as @code{byte-compile-file}. Byte compiled code is usually stored in a file that ends with a @file{.elc} extension rather than a @file{.el} extension. You will see both kinds of file in the @file{emacs/lisp} directory; the files to read are those with @file{.el} extensions. As a practical matter, for most things you might do to customize or extend Emacs, you do not need to byte compile; and I will not discuss the topic here. @xref{Byte Compilation, , Byte Compilation, elisp, The GNU Emacs Lisp Reference Manual}, for a full description of byte compilation. @node Evaluation, Variables, Lisp Interpreter, List Processing @comment node-name, next, previous, up @section Evaluation @cindex Evaluation When the Lisp interpreter works on an expression, the term for the activity is called @dfn{evaluation}. We say that the interpreter `evaluates the expression'. I've used this term several times before. The word comes from its use in everyday language, `to ascertain the value or amount of; to appraise', according to @cite{Webster's New Collegiate Dictionary}. After evaluating an expression, the Lisp interpreter will most likely @dfn{return} the value that the computer produces by carrying out the instructions it found in the function definition, or perhaps it will give up on that function and produce an error message. (The interpreter may also find itself tossed, so to speak, to a different function or it may attempt to repeat continually what it is doing for ever and ever in what is called an `infinite loop'. These actions are less common; and we can ignore them.) Most frequently, the interpreter returns a value. @cindex @samp{side effect} defined At the same time the interpreter returns a value, it may do something else as well, such as move a cursor or copy a file; this other kind of action is called a @dfn{side effect}. Actions that we humans think are important, such as printing results, are often ``side effects'' to the Lisp interpreter. The jargon can sound peculiar, but it turns out that it is fairly easy to learn to use side effects. In summary, evaluating a symbolic expression most commonly causes the Lisp interpreter to return a value and perhaps carry out a side effect; or else produce an error. @menu * Evaluating Inner Lists:: Lists within lists... @end menu @node Evaluating Inner Lists, , Evaluation, Evaluation @comment node-name, next, previous, up @subsection Evaluating Inner Lists @cindex Inner list evaluation @cindex Evaluating inner lists If evaluation applies to a list that is inside another list, the outer list may use the value returned by the first evaluation as information when the outer list is evaluated. This explains why inner expressions are evaluated first: the values they return are used by the outer expressions. We can investigate this process by evaluating another addition example. Place your cursor after the following expression and type @kbd{C-x C-e}: @example (+ 2 (+ 3 3)) @end example @noindent The number 8 will appear in the echo area. What happens is that the Lisp interpreter first evaluates the inner expression, @code{(+ 3 3)}, for which the value 6 is returned; then it evaluates the outer expression as if it were written @code{(+ 2 6)}, which returns the value 8. Since there are no more enclosing expressions to evaluate, the interpreter prints that value in the echo area. Now it is easy to understand the name of the command invoked by the keystrokes @kbd{C-x C-e}: the name is @code{eval-last-sexp}. The letters @code{sexp} are an abbreviation for `symbolic expression', and @code{eval} is an abbreviation for `evaluate'. The command means `evaluate last symbolic expression'. As an experiment, you can try evaluating the expression by putting the cursor at the beginning of the next line immediately following the expression, or inside the expression. Here is another copy of the expression: @example (+ 2 (+ 3 3)) @end example @noindent If you place the cursor at the beginning of the blank line that immediately follows the expression and type @kbd{C-x C-e}, you will still get the value 8 printed in the echo area. Now try putting the cursor inside the expression. If you put it right after the next to last parenthesis (so it appears to sit on top of the last parenthesis), you will get a 6 printed in the echo area! This is because the command evaluates the expression @code{(+ 3 3)}. Now put the cursor immediately after a number. Type @kbd{C-x C-e} and you will get the number itself. In Lisp, if you evaluate a number, you get the number itself---this is how numbers differ from symbols. If you evaluate a list starting with a symbol like @code{+}, you will get a value returned that is the result of the computer carrying out the instructions in the function definition attached to that name. If a symbol by itself is evaluated, something different happens, as we will see in the next section. @node Variables, Arguments, Evaluation, List Processing @comment node-name, next, previous, up @section Variables @cindex Variables In Lisp, a symbol can have a value attached to it just as it can have a function definition attached to it. The two are different. The function definition is a set of instructions that a computer will obey. A value, on the other hand, is something, such as number or a name, that can vary (which is why such a symbol is called a variable). The value of a symbol can be any expression in Lisp, such as a symbol, number, list, or string. A symbol that has a value is often called a @dfn{variable}. A symbol can have both a function definition and a value attached to it at the same time. The two are separate. This is somewhat similar to the way the name Cambridge can refer to the city in Massachusetts and have some information attached to the name as well, such as ``great programming center''. @ignore (Incidentally, in Emacs Lisp, a symbol can have two other things attached to it, too: a property list and a documentation string; these are discussed later.) @end ignore Another way of thinking of this is to imagine a symbol as being a chest of drawers. The function definition is put in one drawer, the value in another, and so on. What is put in the drawer holding the value can be changed without affecting the contents of the drawer holding the function definition, and vice-versa. The variable @code{fill-column} illustrates a symbol with a value attached to it: in every GNU Emacs buffer, this symbol is set to some value, usually 72 or 70, but sometimes to some other value. To find the value of this symbol, evaluate it by itself. If you are reading this in Info inside of GNU Emacs, you can do this by putting the cursor after the symbol and typing @kbd{C-x C-e}: @example fill-column @end example @noindent After I typed @kbd{C-x C-e}, Emacs printed the number 72 in my echo area. This is the value for which @code{fill-column} is set for me as I write this. It may be different for you in your Info buffer. Notice that the value returned as a variable is printed in exactly the same way as the value returned by a function carrying out its instructions. From the point of view of the Lisp interpreter, a value returned is a value returned. What kind of expression it came from ceases to matter once the value is known. A symbol can have any value attached to it or, to use the jargon, we can @dfn{bind} the variable to a value: to a number, such as 72; to a string, @code{"such as this"}; to a list, such as @code{(spruce pine oak)}; we can even bind a variable to a function definition. A symbol can be bound to a value in several ways. @xref{set & setq, , Setting the Value of a Variable}, for information about one way to do this. Notice that there were no parentheses around the word @code{fill-column} when we evaluated it to find its value. This is because we did not intend to use it as a function name. If @code{fill-column} were the first or only element of a list, the Lisp interpreter would attempt to find the function definition attached to it. But @code{fill-column} has no function definition. Try evaluating this: @example (fill-column) @end example @noindent @example @group @exdent You will produce an error message that says: Symbol's function definition is void:@: fill-column @end group @end example @menu * Void Variable:: The error message for a symbol without a value. @end menu @node Void Variable, , Variables, Variables @comment node-name, next, previous, up @subsection Error Message for a Symbol Without a Value @cindex Symbol without value error @cindex Error for symbol without value If you attempt to evaluate a symbol that does not have a value bound to it, you will receive an error message. You can see this by experimenting with our 2 plus 2 addition. In the following expression, put your cursor right after the @code{+}, before the first number 2, type @kbd{C-x C-e}: @example (+ 2 2) @end example @noindent You will get an error message that says: @example Symbol's value as variable is void:@: + @end example @noindent This is different from the first error message we saw, which said, @samp{Symbol's function definition is void:@: this}. In this case, the symbol does not have a value as a variable; in the other case, the symbol (which was the word @samp{this}) did not have a function definition. In this experiment with the @code{+}, what we did was cause the Lisp interpreter to evaluate the @code{+} and look for the value of the variable instead of the function definition. We did this by placing the cursor right after the symbol rather than after the parenthesis of the enclosing list as we did before. As a consequence, the Lisp interpreter evaluated the preceding s-expression, which in this case was the @code{+} by itself. Since @code{+} does not have a value bound to it, just the function definition, the error message reported that the symbol's value as a variable was void. @node Arguments, set & setq, Variables, List Processing @comment node-name, next, previous, up @section Arguments @cindex Arguments @cindex Passing information to functions To see how information is passed to functions, let's look again at our old standby, the addition of two plus two. In Lisp, this is written as follows: @example (+ 2 2) @end example If you evaluate this expression, the number 4 will appear in your echo area. What the Lisp interpreter does is add the numbers that follow the @code{+}. @cindex @samp{argument} defined The numbers added by @code{+} are called the @dfn{arguments} of the function @code{+}. These numbers are the information that is given to or @dfn{passed} to the function. The word `argument' comes from the way it is used in mathematics and does not refer to a disputation between two people; instead it refers to the information presented to the function, in this case, to the @code{+}. In Lisp, the arguments to a function are the atoms or lists that follow the function. The values returned by the evaluation of these atoms or lists are passed to the function. Different functions require different numbers of arguments; some functions require none at all.@footnote{It is curious to track the path by which the word `argument' came to have two different meanings, one in mathematics and the other in everyday English. According to the @cite{Oxford English Dictionary}, the word derives from the Latin for @samp{to make clear, prove}; thus it came to mean, by one thread of derivation, `the evidence offered as proof', which is to say, `the information offered', which led to its meaning in Lisp. But in the other thread of derivation, it came to mean `to assert in a manner against which others may make counter assertions', which led to the meaning of the word as a disputation. (Note here that the English word has two different definitions attached to it at the same time. By contrast, in Emacs Lisp, a symbol cannot have two different function definitions at the same time.)} @menu * Data types:: Types of data passed to a function. * Args as Variable or List:: An argument can be the value of a variable or list. * Variable Number of Arguments:: Some functions may take a variable number of arguments. * Wrong Type of Argument:: Passing an argument of the wrong type to a function. * message:: A useful function for sending messages. @end menu @node Data types, Args as Variable or List, Arguments, Arguments @comment node-name, next, previous, up @subsection Arguments' Data Types @cindex Data types @cindex Types of data @cindex Arguments' data types The type of data that should be passed to a function depends on what kind of information it uses. The arguments to a function such as @code{+} must have values that are numbers, since @code{+} adds numbers. Other functions use different kinds of data for their arguments. @findex concat For example, the @code{concat} function links together or unites two or more strings of text to produce a string. The arguments are strings. Concatenating the two character strings @code{abc}, @code{def} produces the single string @code{abcdef}. This can be seen by evaluating the following: @example (concat "abc" "def") @end example @noindent The value produced by evaluating this expression is @code{"abcdef"}. A function such as @code{substring} uses both a string and numbers as arguments. The function returns a part of the string, a substring of the first argument. This function takes three arguments. Its first argument is the string of characters, the second and third arguments are numbers that indicate the beginning and end of the substring. The numbers are a count of the number of characters (including spaces and punctuations) from the beginning of the string. For example, if you evaluate the following: @example (substring "The quick brown fox jumped." 16 19) @end example @noindent you will see @code{"fox"} appear in the echo area. The arguments are the string and the two numbers. Note that the string passed to @code{substring} is a single atom even though it is made up of several words separated by spaces. Lisp counts everything between the two quotation marks as part of the string, including the spaces. You can think of the @code{substring} function as a kind of `atom smasher' since it takes an otherwise indivisible atom and extracts a part. However, @code{substring} is only able to extract a substring from an argument that is a string, not from another type of atom such as a number or symbol. @node Args as Variable or List, Variable Number of Arguments, Data types, Arguments @comment node-name, next, previous, up @subsection An Argument as the Value of a Variable or List An argument can be a symbol that returns a value when it is evaluated. For example, when the symbol @code{fill-column} by itself is evaluated, it returns a number. This number can be used in an addition. Position the cursor after the following expression and type @kbd{C-x C-e}: @example (+ 2 fill-column) @end example @noindent The value will be a number two more than what you get by evaluating @code{fill-column} alone. For me, this is 74, because the value of @code{fill-column} is 72. As we have just seen, an argument can be a symbol that returns a value when evaluated. In addition, an argument can be a list that returns a value when it is evaluated. For example, in the following expression, the arguments to the function @code{concat} are the strings @w{@code{"The "}} and @w{@code{" red foxes."}} and the list @code{(+ 2 fill-column)}. @example (concat "The " (+ 2 fill-column) " red foxes.") @end example @noindent If you evaluate this expression, @code{"The 74 red foxes."} will appear in the echo area. (Note that you must put spaces after the word @samp{The} and before the word @samp{red} so they will appear in the final string.) @node Variable Number of Arguments, Wrong Type of Argument, Args as Variable or List, Arguments @comment node-name, next, previous, up @subsection Variable Number of Arguments @cindex Variable number of arguments @cindex Arguments, variable number of Some functions, such as @code{concat}, @code{+} or @code{*}, take any number of arguments. (The @code{*} is the symbol for multiplication.) This can be seen by evaluating each of the following expressions in the usual way. What you will see in the echo area is printed in this text after @samp{@result{}}, which you may read as `evaluates to'. @need 1250 In the first set, the functions have no arguments: @example @group (+) @result{} 0 (*) @result{} 1 @end group @end example @need 1250 In this set, the functions have one argument each: @example @group (+ 3) @result{} 3 (* 3) @result{} 3 @end group @end example @need 1250 In this set, the functions have three arguments each: @example @group (+ 3 4 5) @result{} 12 (* 3 4 5) @result{} 60 @end group @end example @node Wrong Type of Argument, message, Variable Number of Arguments, Arguments @comment node-name, next, previous, up @subsection Using the Wrong Type Object as an Argument @cindex Wrong type of argument @cindex Argument, wrong type of When a function is passed an argument of the wrong type, the Lisp interpreter produces an error message. For example, the @code{+} function expects the values of its arguments to be numbers. As an experiment we can pass it the quoted symbol @code{hello} instead of a number. Position the cursor after the following expression and type @kbd{C-x C-e}: @example (+ 2 'hello) @end example @noindent When you do this you will generate an error message. What has happened is that @code{+} has tried to add the 2 to the value returned by @code{'hello}, but the value returned by @code{'hello} is the symbol @code{hello}, not a number. Only numbers can be added. So @code{+} could not carry out its addition. As usual, the error message tries to be helpful and makes sense after you learn how to read it. What it says is this: @example Wrong type argument:@: integer-or-marker-p, hello @end example The first part of the error message is straightforward; it says @samp{Wrong type argument}. Next comes the mysterious jargon word @w{@samp{integer-or-marker-p}}. This word is trying to tell you what kind of argument the @code{+} expected. The symbol @code{integer-or-marker-p} says that the Lisp interpreter is trying to determine whether the information presented it (the value of the argument) is an integer (that is, a whole number) or a marker (a special object representing a buffer position). What it does is test to see whether the @code{+} is being given whole numbers to add. It also tests to see whether the argument is something called a marker, which is a specific feature of Emacs Lisp. (In Emacs, locations in a buffer are recorded as markers. When the mark is set with the @kbd{C-@@} or @kbd{C-@key{SPC}} command, its position is kept as a marker. The mark can be considered a number---the number of characters the location is from the beginning of the buffer.) In Emacs Lisp, @code{+} can be used to add the numeric value of marker positions as numbers. The @samp{p} of @code{integer-or-marker-p} is the embodiment of a practice started in the early days of Lisp programming. The @samp{p} stands for `predicate'. In the jargon used by the early Lisp researchers, a predicate refers to a function to determine whether some property is true or false. So the @samp{p} tells us that @code{integer-or-marker-p} is the name of a function that determines whether it is true or false that the argument supplied is an integer or a marker. Other Lisp symbols that end in @samp{p} include @code{zerop}, a function that tests whether its argument has the value of zero, and @code{listp}, a function that tests whether its argument is a list. Finally, the last part of the error message is the symbol @code{hello}. This is the value of the argument that was passed to @code{+}. If the addition had been passed the correct type of object, the value passed would have been a number, such as 37, rather than a symbol like @code{hello}. But then you would not have got the error message. @node message, , Wrong Type of Argument, Arguments @comment node-name, next, previous, up @subsection The @code{message} Function @findex message Like @code{+}, the @code{message} function takes a variable number of arguments. It is used to send messages to the user and is so useful that we will describe it here. A message is printed in the echo area. For example, you can print a message in your echo area by evaluating the following list: @example (message "This message appears in the echo area!") @end example The whole string between double quotation marks is a single argument and is printed in toto. (Note that in this example, the message itself will appear in the echo area within double quotes; that is because you see the value returned by the @code{message} function. In most uses of @code{message} in programs that you write, the text will be printed in the echo area as a side-effect, without the quotes. @xref{multiply-by-seven in detail, , @code{multiply-by-seven} in detail}, for an example of this.) However, if there is a @samp{%s} in the quoted string of characters, the @code{message} function does not print the @samp{%s} as such, but looks to the argument that follows the string. It evaluates the second argument and prints the value in the location in the string where the @samp{%s} is. You can see this by positioning the cursor after the following expression and typing @kbd{C-x C-e}: @example (message "The name of this buffer is: %s." (buffer-name)) @end example @noindent In Info, @code{"The name of this buffer is: *info*."} will appear in the echo area. The function @code{buffer-name} returns the name of the buffer as a string, which the @code{message} function inserts in place of @code{%s}. To print a value as a decimal number, use @samp{%d} in the same way as @samp{%s}. For example, to print a message in the echo area that states the value of the @code{fill-column}, evaluate the following: @example (message "The value of fill-column is %d." fill-column) @end example @noindent On my system, when I evaluate this list, @code{"The value of fill-column is 72."} appears in my echo area. If there is more than one @samp{%s} in the quoted string, the value of the first argument following the quoted string is printed at the location of the first @samp{%s} and the value of the second argument is printed at the location of the second @samp{%s}, and so on. For example, if you evaluate the following, @example @group (message "There are %d %s in the office!" (- fill-column 14) "pink elephants") @end group @end example @noindent a rather whimsical message will appear in your echo area. On my system it says, @code{"There are 58 pink elephants in the office!"}. The expression @code{(- fill-column 14)} is evaluated and the resulting number is inserted in place of the @samp{%d}; and the string in double quotes, @code{"pink elephants"}, is treated as a single argument and inserted in place of the @samp{%s}. (That is to say, a string between double quotes evaluates to itself, like a number.) Finally, here is a somewhat complex example that not only illustrates the computation of a number, but also shows how you can use an expression within an expression to generate the text that is substituted for @samp{%s}: @example @group (message "He saw %d %s" (- fill-column 34) (concat "red " (substring "The quick brown foxes jumped." 16 21) " leaping.")) @end group @end example In this example, @code{message} has three arguments: the string, @code{"He saw %d %s"}, the expression, @code{(- fill-column 32)}, and the expression beginning with the function @code{concat}. The value resulting from the evaluation of @code{(- fill-column 32)} is inserted in place of the @samp{%d}; and the value returned by the expression beginning with @code{concat} is inserted in place of the @samp{%s}. When I evaluate the expression, the message, @code{"He saw 38 red foxes leaping."}, appears in my echo area. @node set & setq, Summary, Arguments, List Processing @comment node-name, next, previous, up @section Setting the Value of a Variable @cindex Variable, setting value @cindex Setting value of variable @cindex @samp{bind} defined There are several ways by which a variable can be given a value. One of the ways is to use either the function @code{set} or the function @code{setq}. Another way is to use @code{let} (@pxref{let}). (The jargon for this process is to @dfn{bind} a variable to a value.) The following sections not only describe how @code{set} and @code{setq} work but also illustrate how arguments are passed. @menu * Using set:: Setting values. * Using setq:: Setting a quoted value. * Counting:: Using @code{setq} to count. @end menu @node Using set, Using setq, set & setq, set & setq @comment node-name, next, previous, up @subsection Using @code{set} @findex set To set the value of the symbol @code{flowers} to the list @code{'(rose violet daisy buttercup)}, evaluate the following expression by positioning the cursor after the expression and typing @kbd{C-x C-e}. @example (set 'flowers '(rose violet daisy buttercup)) @end example @noindent The list @code{(rose violet daisy buttercup)} will appear in the echo area. This is what is @emph{returned} by the @code{set} function. As a side effect, the symbol @code{flowers} is bound to the list ; that is, the symbol @code{flowers}, which can be viewed as a variable, is given the list as its value. (This process, by the way, illustrates how a side effect to the Lisp interpreter, setting the value, can be the primary effect that we humans are interested in. This is because every Lisp function must return a value if it does not get an error, but it will only have a side effect if it is designed to have one.) After evaluating the @code{set} expression, you can evaluate the symbol @code{flowers} and it will return the value you just set. Here is the symbol. Place your cursor after it and type @kbd{C-x C-e}. @example flowers @end example @noindent When you evaluate @code{flowers}, the list @code{(rose violet daisy buttercup)} appears in the echo area. Incidentally, if you evaluate @code{'flowers}, the variable with a quote in front of it, what you will see in the echo area is the symbol itself, @code{flowers}. Here is the quoted symbol, so you can try this: @example 'flowers @end example Note also, that when you use @code{set}, you need to quote both arguments to @code{set}, unless you want them evaluated. In this case, we do not want either argument evaluated, neither the variable @code{flowers} nor the list @code{(rose violet daisy buttercup)}, so both are quoted. (When you use @code{set} without quoting its first argument, the first argument is evaluated before anything else is done. If you did this and @code{flowers} did not have a value already, you would get an error message that the @samp{Symbol's value as variable is void}; on the other hand, if @code{flowers} did return a value after it was evaluated, the @code{set} would attempt to set the value that was returned. There are situations where this is the right thing for the function to do; but such situations are rare.) @node Using setq, Counting, Using set, set & setq @comment node-name, next, previous, up @subsection Using @code{setq} @findex setq As a practical matter, you almost always quote the first argument to @code{set}. The combination of @code{set} and a quoted first argument is so common that it has its own name: the special form @code{setq}. This special form is just like @code{set} except that the first argument is quoted automatically, so you don't need to type the quote mark yourself. Also, as an added convenience, @code{setq} permits you to set several different variables to different values, all in one expression. To set the value of the variable @code{carnivores} to the list @code{'(lion tiger leopard)} using @code{setq}, the following expression is used: @example (setq carnivores '(lion tiger leopard)) @end example @noindent This is exactly the same as using @code{set} except the first argument is automatically quoted by @code{setq}. (The @samp{q} in @code{setq} means @code{quote}.) With @code{set}, the expression would look like this: @example (set 'carnivores '(lion tiger leopard)) @end example Also, @code{setq} can be used to assign different values to different variables. The first argument is bound to the value of the second argument, the third argument is bound to the value of the fourth argument, and so on. For example, you could use the following to assign a list of trees to the symbol @code{trees} and a list of herbivores to the symbol @code{herbivores}: @example @group (setq trees '(pine fir oak maple) herbivores '(gazelle antelope zebra)) @end group @end example @noindent (The expression could just as well have been on one line, but it might not have fit on a page; and humans find it easier to read nicely formatted lists.) Although I have been using the term `assign', there is another way of thinking about the workings of @code{set} and @code{setq}; and that to say that @code{set} and @code{setq} make the symbol @emph{point} to the list. This latter way of thinking is very common and in forthcoming chapters we shall come upon at least one symbol that has `pointer' as part of its name. The name is chosen because the symbol has a value, specifically a list, attached to it; or, expressed in this other way, the symbol is set to ``point'' to the list. @node Counting, , Using setq, set & setq @comment node-name, next, previous, up @subsection Counting @cindex Counting Here is an example that shows how to use @code{setq} in a counter. You might use this to count how many times a part of your program repeats itself. First set a variable to zero; then add one to the number each time the program repeats itself. To do this, you need a variable that serves as a counter, and two expressions: an initial @code{setq} expression that sets the counter variable to zero; and a second @code{setq} expression that increments the counter each time it is evaluated. @example @group (setq counter 0) ; @r{Let's call this the initializer.} (setq counter (+ counter 1)) ; @r{This is the incrementer.} counter ; @r{This is the counter.} @end group @end example @noindent (The text following the @samp{;} are comments. @xref{Change a defun, , Change a Function Definition}.) If you evaluate the first of these expressions, the initializer, @code{(setq counter 0)}, and then evaluate the third expression, @code{counter}, the number @code{0} will appear in the echo area. If you then evaluate the second expression, the incrementer, @code{(setq counter (+ counter 1))}, the counter will get the value 1. So if you again evaluate @code{counter}, the number @code{1} will appear in the echo area. Each time you evaluate the second expression, the value of the counter will be incremented. When you evaluate the incrementer, @code{(setq counter (+ counter 1))}, the Lisp interpreter first evaluates the innermost list; this is the addition. In order to evaluate this list, it must evaluate the variable @code{counter} and the number @code{1}. When it evaluates the variable @code{counter}, it receives its current value. It passes this value and the number @code{1} to the @code{+} which adds them together. The sum is then returned as the value of the inner list and passed to the @code{setq} which sets the variable @code{counter} to this new value. Thus, the value of the variable, @code{counter}, is changed. @node Summary, Error Message Exercises, set & setq, List Processing @comment node-name, next, previous, up @section Summary Learning Lisp is like climbing a hill in which the first part is the steepest. You have now climbed the most difficult part; what remains becomes easier as you progress onwards. In summary, @itemize @bullet @item Lisp programs are made up of expressions, which are lists or single atoms. @item Lists are made up of zero or more atoms or inner lists, separated by whitespace and surrounded by parentheses. A list can be empty. @item Atoms are multi-character symbols, like @code{forward-paragraph}, single character symbols like @code{+}, strings of characters between double quotation marks, or numbers. @item A number evaluates to itself. @item A string between double quotes also evaluates to itself. @item When you evaluate a symbol by itself, its value is returned. @item When you evaluate a list, the Lisp interpreter looks at the first symbol in the list and then at the function definition bound to that symbol. Then the instructions in the function definition are carried out. @item A single-quote, @code{'}, tells the Lisp interpreter that it should return the following expression as written, and not evaluate it as it would if the quote were not there. @item Arguments are the information passed to a function. The arguments to a function are computed by evaluating the rest of the elements of the list of which the function is the first element. @item A function always returns a value when it is evaluated (unless it gets an error); in addition, it may also carry out some action called a ``side effect''. In many cases, a function's primary purpose is to create a side effect. @end itemize @node Error Message Exercises, , Summary, List Processing @comment node-name, next, previous, up @section Exercises A few simple exercises: @itemize @bullet @item Generate an error message by evaluating an appropriate symbol that is not within parentheses. @item Generate an error message by evaluating an appropriate symbol that is between parentheses. @item Create a counter that increments by two rather than one. @item Write an expression that prints a message in the echo area when evaluated. @end itemize @node Practicing Evaluation, Writing Defuns, List Processing, Top @comment node-name, next, previous, up @chapter Practicing Evaluation @cindex Practicing evaluation @cindex Evaluation practice Before learning how to write a function definition in Emacs Lisp, it is useful to spend a little time evaluating various expressions that have already been written. These expressions will be lists with the functions as their first (and often only) element. Since some of the functions associated with buffers are both simple and interesting, we will start with those. In this section, we will evaluate a few of these. In another section, we will study the code of several other buffer-related functions, to see how they were written. @menu * How to Evaluate:: Typing editing commands or @kbd{C-x C-e} causes evaluation. * Buffer Names:: Buffers and files are different. * Getting Buffers:: Getting a buffer itself, not merely its name. * Switching Buffers:: How to change to another buffer. * Buffer Size & Locations:: Where point is located and the size of the buffer. * Evaluation Exercise:: @end menu @node How to Evaluate, Buffer Names, Practicing Evaluation, Practicing Evaluation @ifinfo @heading How to Evaluate @end ifinfo @i{Whenever you give an editing command} to Emacs Lisp, such as the command to move the cursor or to scroll the screen, @i{you are evaluating an expression,} the first element of which is the function. @i{This is how Emacs works.} @cindex @samp{interactive function} defined @cindex @samp{command} defined When you type keys, you cause the Lisp interpreter to evaluate an expression and that is how you get your results. Even typing plain text involves evaluating an Emacs Lisp function, in this case, one that uses @code{self-insert-command}, which simply inserts the character you typed. The functions you evaluate by typing keystrokes are called @dfn{interactive} functions, or @dfn{commands}; how you make a function interactive will be illustrated in the chapter on how to write function definitions. @xref{Interactive, , Making a Function Interactive}. In addition to typing keyboard commands, we have seen a second way to evaluate an expression: by positioning the cursor after a list and typing @kbd{C-x C-e}. This is what we will do in the rest of this section. There are other ways to evaluate an expression as well; these ways will be described in other sections as we come to them. Besides being used for practicing evaluation, the functions shown in the next few sections are important in their own right. A study of these functions makes clear the distinction between buffers and files, how to switch to a buffer, and how to determine a location within it. @node Buffer Names, Getting Buffers, How to Evaluate, Practicing Evaluation @comment node-name, next, previous, up @section Buffer Names @findex buffer-name @findex buffer-file-name The two functions, @code{buffer-name} and @code{buffer-file-name}, show the difference between a file and a buffer. When you evaluate the following expression, @code{(buffer-name)}, the name of the buffer appears in the echo area. When you evaluate @code{(buffer-file-name)}, the name of the file to which the buffer refers appears in the echo area. Usually, the name returned by @code{(buffer-name)} is the same as the name of the file to which it refers, and the name returned by @code{(buffer-file-name)} is the full path-name of the file. A file and a buffer are two different entities. A file is information recorded permanently in the computer (unless you delete it). A buffer, on the other hand, is information inside of Emacs that will vanish at the end of the editing session (or when you kill the buffer). Usually, a buffer contains information that you have copied from a file; we say the buffer is @dfn{visiting} that file. This copy is what you work on and modify. Changes to the buffer do not change the file, until you save the buffer. When you save the buffer, the buffer is copied to the file and is thus saved permanently. If you are reading this in Info inside of GNU Emacs, you can evaluate each of the following expressions by positioning the cursor after it and typing @kbd{C-x C-e}. @example @group (buffer-name) (buffer-file-name) @end group @end example @noindent When I do this, @file{"introduction.texinfo"} is the value returned by evaluating @code{(buffer-name)}, and @file{"/gnu/work/intro/introduction.texinfo"} is the value returned by evaluating @code{(buffer-file-name)}. The former is the name of the buffer and the latter is the name of the file. (In the expressions, the parentheses tell the Lisp interpreter to treat @code{buffer-name} and @code{buffer-file-name} as functions; without the parentheses, the interpreter would attempt to evaluate the symbols as variables. @xref{Variables}.) In spite of the distinction between files and buffers, you will often find that people refer to a file when they mean a buffer and vice-versa. Indeed, most people say, ``I am editing a file,'' rather than saying, ``I am editing a buffer which I will soon save to a file.'' It is almost always clear from context what people mean. When dealing with computer programs, however, it is important to keep the distinction in mind, since the computer is not as smart as a person. @cindex Buffer, history of word The word `buffer', by the way, comes from the meaning of the word as a cushion that deadens the force of a collision. In early computers, a buffer cushioned the interaction between files and the computer's central processing unit. The drums or tapes that held a file and the central processing unit were pieces of equipment that were very different from each other, working at their own speeds, in spurts. The buffer made it possible for them to work together effectively. Eventually, the buffer grew from being an intermediary, a temporary holding place, to being the place where work is done. This transformation is rather like that of a small seaport that grew into a great city: once it was merely the place where cargo was warehoused temporarily before being loaded onto ships; then it became a business and cultural center in its own right. Not all buffers are associated with files. For example, when you start an Emacs session by typing the command @code{emacs} alone, without naming any files, Emacs will start with the @file{*scratch*} buffer on the screen. This buffer is not visiting any file. Similarly, a @file{*Help*} buffer is not associated with any file. @cindex @code{nil}, history of word If you switch to the @file{*scratch*} buffer, type @code{(buffer-name)}, position the cursor after it, and type @kbd{C-x C-e} to evaluate the expression, the name @code{"*scratch*"} is returned and will appear in the echo area. @code{"*scratch*"} is the name of the buffer. However, if you type @code{(buffer-file-name)} in the @file{*scratch*} buffer and evaluate that, @code{nil} will appear in the echo area. @code{nil} is from the Latin word for `nothing'; in this case, it means that the @file{*scratch*} buffer is not associated with any file. (In Lisp, @code{nil} is also used to mean `false' and is a synonym for the empty list, @code{()}.) Incidentally, if you are in the @file{*scratch*} buffer and want the value returned by an expression to appear in the @file{*scratch*} buffer itself rather than in the echo area, type @kbd{C-u C-x C-e} instead of @kbd{C-x C-e}. This causes the value returned to appear after the expression. The buffer will look like this: @example (buffer-name)"*scratch*" @end example @noindent You cannot do this in Info since Info is read-only and it will not allow you to change the contents of the buffer. But you can do this in any buffer you can edit; and when you write code or documentation (such as this manual), this feature is very useful. @node Getting Buffers, Switching Buffers, Buffer Names, Practicing Evaluation @comment node-name, next, previous, up @section Getting Buffers @findex current-buffer @findex other-buffer @cindex Getting a buffer The @code{buffer-name} function returns the @emph{name} of the buffer; to get the buffer @emph{itself}, a different function is needed: the @code{current-buffer} function. If you use this function in code, what you get is the buffer itself. A name and the object or entity to which the name refers are different from each other. You are not your name. You are a person to whom others refer by name. If you ask to speak to George and someone hands you a card with the letters @samp{G}, @samp{e}, @samp{o}, @samp{r}, @samp{g}, and @samp{e} written on it, you might be amused, but you would not be satisfied. You do not want to speak to the name, but to the person to whom the name refers. A buffer is similar: the name of the scratch buffer is @file{*scratch*}, but the name is not the buffer. To get a buffer itself, you need to use a function such as @code{current-buffer}. However, there is a slight complication: if you evaluate @code{current-buffer} in an expression on its own, as we will do here, what you see is a printed representation of the name of the buffer without the contents of the buffer. Emacs works this way for two reasons: the buffer may be thousands of lines long---too long to be conveniently displayed; and, another buffer may have the same contents but a different name, and it is important to distinguish between them. Here is an expression containing the function: @example (current-buffer) @end example @noindent If you evaluate the expression in the usual way, @file{#} appears in the echo area. The special format indicates that the buffer itself is being returned, rather than just its name. Incidentally, while you can type a number or symbol into a program, you cannot do that with the printed representation of a buffer: the only way to get a buffer itself is with a function such as @code{current-buffer}. A related function is @code{other-buffer}. This returns the most recently selected buffer other than the one you are in currently. If you have recently switched back and forth from the @file{*scratch*} buffer, @code{other-buffer} will return that buffer. You can see this by evaluating the expression: @example (other-buffer) @end example @noindent You should see @file{#} appear in the echo area, or the name of whatever other buffer you switched back from most recently. @node Switching Buffers, Buffer Size & Locations, Getting Buffers, Practicing Evaluation @comment node-name, next, previous, up @section Switching Buffers @findex switch-to-buffer @findex set-buffer @cindex Switching to a buffer The @code{other-buffer} function actually provides a buffer when it is used as an argument to a function that requires one. We can see this by using @code{other-buffer} and @code{switch-to-buffer} to switch to a different buffer. But first, a brief introduction to the @code{switch-to-buffer} function. When you switched back and forth from Info to the @file{*scratch*} buffer to evaluate @code{(buffer-name)}, you most likely typed @kbd{C-x b} and then typed @file{*scratch*} when prompted in the minibuffer for the name of the buffer to which you wanted to switch. The keystrokes, @kbd{C-x b}, cause the Lisp interpreter to evaluate the interactive Emacs Lisp function @code{switch-to-buffer}. As we said before, this is how Emacs works: different keystrokes call or run different functions. For example, @kbd{C-f} calls @code{forward-char}, @kbd{M-e} calls @code{forward-sentence}, and so on. By writing @code{switch-to-buffer} in an expression, and giving it a buffer to switch to, we can switch buffers just the way @kbd{C-x b} does. @need 1000 Here is the Lisp expression: @example (switch-to-buffer (other-buffer)) @end example @noindent The symbol @code{switch-to-buffer} is the first element of the list, so the Lisp interpreter will treat it as a function and carry out the instructions that are attached to it. But before doing that, the interpreter will note that @code{other-buffer} is inside parentheses and work on that symbol first. @code{other-buffer} is the first (and in this case, the only) element of this list, so the Lisp interpreter calls or runs the function. It returns another buffer. Next, the interpreter runs @code{switch-to-buffer}, passing to it, as an argument, the other buffer, which is what Emacs will switch to. If you are reading this in Info, try this now. Evaluate the expression. (To get back, type @kbd{C-x b @key{RET}}.) In the programming examples in later sections of this document, you will see the function @code{set-buffer} more often than @code{switch-to-buffer}. This is because of a difference between computer programs and humans: humans have eyes and expect to see the buffer on which they are working on their computer terminals. This is so obvious, it almost goes without saying. However, programs do not have eyes. When a computer program works on a buffer, that buffer does not need to be visible on the screen. @code{switch-to-buffer} is designed for humans and does two different things: it switches the buffer to which Emacs attention is directed; and it switches the buffer displayed in the window to the new buffer. @code{set-buffer}, on the other hand, does only one thing: it switches the attention of the computer program to a different buffer. The buffer on the screen remains unchanged (of course, normally nothing happens there until the command finishes running). @cindex @samp{call} defined Also, we have just introduced another jargon term, the word @dfn{call}. When you evaluate a list in which the first symbol is a function, you are calling that function. The use of the term comes from the notion of the function as an entity that can do something for you if you `call' it---just as a plumber is an entity who can fix a leak if you call him or her. @node Buffer Size & Locations, Evaluation Exercise, Switching Buffers, Practicing Evaluation @comment node-name, next, previous, up @section Buffer Size and the Location of Point @cindex Size of buffer @cindex Buffer size @cindex Point location @cindex Location of point Finally, let's look at several rather simple functions, @code{buffer-size}, @code{point}, @code{point-min}, and @code{point-max}. These give information about the size of a buffer and the location of point within it. The function @code{buffer-size} tells you the size of the current buffer; that is, the function returns a count of the number of characters in the buffer. @example (buffer-size) @end example @noindent You can evaluate this in the usual way, by positioning the cursor after the expression and typing @kbd{C-x C-e}. @cindex @samp{point} defined In Emacs, the current position of the cursor is called @dfn{point}. The expression @code{(point)} returns a number that tells you where the cursor is located as a count of the number of characters from the beginning of the buffer up to point. You can see the character count for point in this buffer by evaluating the following expression in the usual way: @example (point) @end example @noindent As I write this, the value of @code{point} is 65724. The @code{point} function is frequently used in some of the examples later in this manual. The value of point depends, of course, on its location within the buffer. If you evaluate point in this spot, the number will be larger: @example (point) @end example @noindent For me, the value of point in this location is 66043, which means that there are 319 characters (including spaces) between the two expressions. @cindex @samp{narrowing} defined The function @code{point-min} is somewhat similar to @code{point}, but it returns the value of the minimum permissible value of point in the current buffer. This is the number 1 unless @dfn{narrowing} is in effect. (Narrowing is a mechanism whereby you can restrict yourself, or a program, to operations on just a part of a buffer. @xref{Narrowing & Widening, , Narrowing and Widening}.) Likewise, the function @code{point-max} returns the value of the maximum permissible value of point in the current buffer. @node Evaluation Exercise, , Buffer Size & Locations, Practicing Evaluation @section Exercise Find a file with which you are working and move towards its middle. Find its buffer name, file name, length, and your position in the file. @node Writing Defuns, Buffer Walk Through, Practicing Evaluation, Top @comment node-name, next, previous, up @chapter How To Write Function Definitions @cindex Definition writing @cindex Function definition writing @cindex Writing a function definition When the Lisp interpreter evaluates a list, it looks to see whether the first symbol on the list has a function definition attached to it; or, put another way, whether the symbol points to a function definition. If it does, the computer carries out the instructions in the definition. A symbol that has a function definition is called, simply, a function (although, properly speaking, the definition is the function and the symbol refers to it.) @menu * Primitive Functions:: Some functions are written in C. * defun:: The @code{defun} special form. * Install:: Install a Function Definition. * Interactive:: Making a function interactive. * Interactive Options:: Different options for @code{interactive}. * Permanent Installation:: Installing code permanently. * let:: Creating and initializing local variables. * if:: What if? * else:: If--then--else expressions. * Truth & Falsehood:: What Lisp considers false and true. * save-excursion:: Keeping track of point, mark, and buffer. * Review:: * defun Exercises:: @end menu @node Primitive Functions, defun, Writing Defuns, Writing Defuns @ifinfo @heading An Aside about Primitive Functions @end ifinfo @cindex Primitive functions @cindex Functions, primitive @cindex C language primitives @cindex Primitives written in C All functions are defined in terms of other functions, except for a few @dfn{primitive} functions that are written in the C programming language. When you write functions' definitions, you will write them in Emacs Lisp and use other functions as your building blocks. Some of the functions you will use will themselves be written in Emacs Lisp (perhaps by you) and some will be primitives written in C. The primitive functions are used exactly like those written in Emacs Lisp and behave like them. They are written in C so we can easily run GNU Emacs on any computer that has sufficient power and can run C. Let me re-emphasize this: when you write code in Emacs Lisp, you do not distinguish between the use of functions written in C and the use of functions written in Emacs Lisp. The difference is irrelevant. I mention the distinction only because it is interesting to know. Indeed, unless you investigate, you won't know whether an already-written function is written in Emacs Lisp or C. @node defun, Install, Primitive Functions, Writing Defuns @comment node-name, next, previous, up @section The @code{defun} Special Form @findex defun @cindex Special form of @code{defun} @cindex @samp{function definition} defined In Lisp, a symbol such as @code{mark-whole-buffer} has code attached to it that tells the computer what to do when the function is called. This code is called the @dfn{function definition} and is created by evaluating a Lisp expression that starts with the symbol @code{defun} (which is an abbreviation for @emph{define function}). Because @code{defun} does not evaluate its arguments in the usual way, it is called a @dfn{special form}. In subsequent sections, we will look at function definitions from the Emacs source code, such as @code{mark-whole-buffer}. In this section, we will describe a simple function definition so you can see how it looks. This function definition uses arithmetic because it makes for a simple example. Some people dislike examples using arithmetic; however, if you are such a person, do not despair. Hardly any of the code we will study in the remainder of this introduction involves arithmetic or mathematics. The examples mostly involve text in one way or another. A function definition has up to five parts following the word @code{defun}: @enumerate @item The name of the symbol to which the function definition should be attached. @item A list of the arguments that will be passed the function. If no arguments will be passed to the function, this is an empty list, @code{()}. @item Documentation describing the function. (Technically optional, but strongly recommended.) @item Optionally, an expression to make the function interactive so you can use it by typing @kbd{M-x} and then the name of the function; or by typing an appropriate key or keychord. @cindex @samp{body} defined @item The code that instructs the computer what to do: the @dfn{body} of the function definition. @end enumerate It is helpful to think of the five parts of a function definition as being organized in a template, with slots for each part: @example @group (defun @var{function-name} (@var{arguments}@dots{}) "@var{optional-documentation}@dots{}" (interactive @var{argument-passing-info}) ; @r{optional} @var{body}@dots{}) @end group @end example As an example, here is the code for a function that multiplies its argument by 7. (This example is not interactive. @xref{Interactive, , Making a Function Interactive}, for that information.) @example @group (defun multiply-by-seven (number) "Multiply NUMBER by seven." (* 7 number)) @end group @end example This definition begins with a parenthesis and the symbol @code{defun}, followed by the name of the function. @cindex @samp{argument list} defined The name of the function is followed by a list that contains the arguments that will be passed to the function. This list is called the @dfn{argument list}. In this case, the list has only one element, the symbol, @code{number}. When the function is used, the symbol will be bound to the value that is used as the argument to the function. Instead of choosing the word @code{number} for the name of the argument, I could have picked any other name. For example, I could have chosen the word @code{multiplicand}. I picked the word `number' because it tells what kind of value is intended for this slot; but I could just as well have chosen the word `multiplicand' to indicate the role that the value placed in this slot will play in the workings of the function. I could have called it @code{foogle}, but that would have been a bad choice because it would not tell humans what it means. The choice of name is up to the programmer and should be chosen to make the meaning of the function clear. Indeed, you can choose any name you wish for a symbol in an argument list, even the name of a symbol used in some other function: the name you use in an argument list is private to that particular definition. In that definition, the name refers to a different entity than any use of the same name outside the function definition. Suppose you have a nick-name `Shorty' in your family; when your family members refer to `Shorty', they mean you. But outside your family, in a movie, for example, the name `Shorty' refers to someone else. Because a name in an argument list is private to the function definition, you can change the value of such a symbol inside the body of a function without changing its value outside the function. The effect is similar to that produced by a @code{let} expression. (@xref{let, , @code{let}}.) @ignore Note also that we discuss the word `number' in two different ways: as a symbol that appears in the code, and as the name of something that will be replaced by a something else during the evaluation of the function. In the first case, @code{number} is a symbol, not a number; it happens that within the function, it is a variable who value is the number in question, but our primary interest in it is as a symbol. On the other hand, when we are talking about the function, our interest is that we will substitute a number for the word @var{number}. To keep this distinction clear, we use different typography for the two circumstances. When we talk about this function, or about how it works, we refer to this number by writing @var{number}. In the function itself, we refer to it by writing @code{number}. @end ignore The argument list is followed by the documentation string that describes the function. This is what you see when you type @w{@kbd{C-h f}} and the name of a function. Incidentally, when you write a documentation string like this, you should make the first line a complete sentence since some commands, such as @code{apropos}, print only the first line of a multi-line documentation string. Also, you should not indent the second line of a documentation string, if you have one, because that looks odd when you use @kbd{C-h f} (@code{describe-function}). The documentation string is optional, but it is so useful, it should be included in almost every function you write. @findex * @r{(multiplication)} The third line of the example consists of the body of the function definition. (Most functions' definitions, of course, are longer than this.) In this case, the body is the list, @code{(* 7 number)}, which says to multiply the value of @var{number} by 7. (In Emacs Lisp, @code{*} is the function for multiplication, just as @code{+} is the function for addition.) When you use the @code{multiply-by-seven} function, the argument @code{number} evaluates to the actual number you want used. Here is an example that shows how @code{multiply-by-seven} is used; but don't try to evaluate this yet! @example (multiply-by-seven 3) @end example @noindent The symbol @code{number}, specified in the function definition in the next section, is given or ``bound to'' the value 3 in the actual use of the function. Note that although @code{number} was inside parentheses in the function definition, the argument passed to the @code{multiply-by-seven} function is not in parentheses. The parentheses are written in the function definition so the computer can figure out where the argument list ends and the rest of the function definition begins. If you evaluate this example, you are likely to get an error message. (Go ahead, try it!) This is because we have written the function definition, but not yet told the computer about the definition---we have not yet installed (or `loaded') the function definition in Emacs. Installing a function is the process that tells the Lisp interpreter the definition of the function. Installation is described in the next section. @node Install, Interactive, defun, Writing Defuns @comment node-name, next, previous, up @section Install a Function Definition @cindex Install a Function Definition @cindex Definition installation @cindex Function definition installation If you are reading this inside of Info in Emacs, you can try out the @code{multiply-by-seven} function by first evaluating the function definition and then evaluating @code{(multiply-by-seven 3)}. A copy of the function definition follows. Place the cursor after the last parenthesis of the function definition and type @kbd{C-x C-e}. When you do this, @code{multiply-by-seven} will appear in the echo area. (What this means is that when a function definition is evaluated, the value it returns is the name of the defined function.) At the same time, this action installs the function definition. @example @group (defun multiply-by-seven (number) "Multiply NUMBER by seven." (* 7 number)) @end group @end example @noindent By evaluating this @code{defun}, you have just installed @code{multiply-by-seven} in Emacs. The function is now just as much a part of Emacs as @code{forward-word} or any other editing function you use. (@code{multiply-by-seven} will stay installed until you quit Emacs. To reload code automatically whenever you start Emacs, see @ref{Permanent Installation, , Installing Code Permanently}.) You can see the effect of installing @code{multiply-by-seven} by evaluating the following sample. Place the cursor after the following expression and type @kbd{C-x C-e}. The number 21 will appear in the echo area. @example (multiply-by-seven 3) @end example If you wish, you can read the documentation for the function by typing @kbd{C-h f} (@code{describe-function}) and then the name of the function, @code{ multiply-by-seven}. When you do this, a @file{*Help*} window will appear on your screen that says: @example @group multiply-by-seven: Multiply NUMBER by seven. @end group @end example @noindent (To return to a single window on your screen, type @kbd{C-x 1}.) @menu * Change a defun:: How to change a function definition. @end menu @node Change a defun, , Install, Install @comment node-name, next, previous, up @subsection Change a Function Definition @cindex Changing a function definition @cindex Function definition, how to change @cindex Definition, how to change If you want to change the code in @code{multiply-by-seven}, just rewrite it. To install the new version in place of the old one, evaluate the function definition again. This is how you modify code in Emacs. It is very simple. As an example, you can change the @code{multiply-by-seven} function to add the number to itself seven times instead of multiplying the number by seven. The produces the same answer, but by a different path. At the same time, we will add a comment to the code; a comment is text that the Lisp interpreter ignores, but that a human reader may find useful or enlightening. In this case the comment is that this is the ``second version''. @example @group (defun multiply-by-seven (number) ; @r{Second version.} "Multiply NUMBER by seven." (+ number number number number number number number)) @end group @end example @cindex Comments in Lisp code The comment follows a semicolon, @samp{;}. In Lisp, everything on a line that follows a semicolon is a comment. The end of the line is the end of the comment. To stretch a comment over two or more lines, begin each line with a semicolon. @xref{Beginning a .emacs File, , Beginning a @file{.emacs} File}, and @ref{Comments, , Comments, elisp, The GNU Emacs Lisp Reference Manual}, for more about comments. You can install this version of the @code{multiply-by-seven} function by evaluating it in the same way you evaluated the first function: place the cursor after the last parenthesis and type @kbd{C-x C-e}. In summary, this is how you write code in Emacs Lisp: you write a function; install it; test it; and then make fixes or enhancements and install it again. @node Interactive, Interactive Options, Install, Writing Defuns @comment node-name, next, previous, up @section Make a Function Interactive @cindex Interactive functions @findex interactive You make a function interactive by placing a list that begins with the special form @code{interactive} immediately after the documentation. A user can invoke an interactive function by typing @kbd{M-x} and then the name of the function; or by typing the keys to which it is bound, for example, by typing @kbd{C-n} for @code{next-line} or @kbd{C-x h} for @code{mark-whole-buffer}. Interestingly, when you call an interactive function interactively, the value returned is not automatically displayed in the echo area. This is because you often call an interactive function for its side effects, such as moving forward by a word or line, and not for the value returned. If the returned value were displayed in the echo area each time you typed a key, it would be very distracting. Both the use of the special form @code{interactive} and one way to display a value in the echo area can be illustrated by creating an interactive version of @code{multiply-by-seven}. @need 1250 Here is the code: @example @group (defun multiply-by-seven (number) ; @r{Interactive version.} "Multiply NUMBER by seven." (interactive "p") (message "The result is %d" (* 7 number))) @end group @end example @noindent You can install this code by placing your cursor after it and typing @kbd{C-x C-e}. The name of the function will appear in your echo area. Then, you can use this code by typing @kbd{C-u} and a number and then typing @kbd{M-x multiply-by-seven} and pressing @key{RET}. The phrase @samp{The result is @dots{}} followed by the product will appear in the echo area. Speaking more generally, you invoke a function like this in either of two ways: @enumerate @item By typing a prefix argument that contains the number to be passed, and then typing @kbd{M-x} and the name of the function, as with @kbd{C-u 3 M-x forward-sentence}; or, @item By typing whatever key or keychord the function is bound to, as with @kbd{C-u 3 M-e}. @end enumerate @noindent Both the examples just mentioned work identically to move point forward three sentences. (Since @code{multiply-by-seven} is not bound to a key, it could not be used as an example of key binding.) (@xref{Keybindings, , Some Keybindings}, to learn how to bind a command to a key.) A prefix argument is passed to an interactive function by typing the @key{META} key followed by a number, for example, @kbd{M-3 M-e}, or by typing @kbd{C-u} and then a number, for example, @kbd{C-u 3 M-e} (if you type @kbd{C-u} without a number, it defaults to 4). @menu * multiply-by-seven in detail:: The interactive version. @end menu @node multiply-by-seven in detail, , Interactive, Interactive @comment node-name, next, previous, up @subsection An Interactive @code{multiply-by-seven}. Let's look at the use of the special form @code{interactive} and then at the function @code{message} in the interactive version of @code{multiply-by-seven}. You will recall that the function definition looks like this: @example @group (defun multiply-by-seven (number) ; @r{Interactive version.} "Multiply NUMBER by seven." (interactive "p") (message "The result is %d" (* 7 number))) @end group @end example In this function, the expression, @code{(interactive "p")}, is a list of two elements. The @code{"p"} tells Emacs to pass the prefix argument to the function and use its value for the argument of the function. The argument will be a number. This is means that the symbol @code{number} will be bound to a number in the line: @example (message "The result is %d" (* 7 number)) @end example @noindent For example, if your prefix argument is 5, the Lisp interpreter will evaluate the line as if it were: @example (message "The result is %d" (* 7 5)) @end example @noindent (If you are reading this in GNU Emacs, you can evaluate this expression yourself.) First, the interpreter will evaluate the inner list, which is @code{(* 7 5)}. This returns a value of 35. Next, it will evaluate the outer list, passing the values of the second and subsequent elements of the list to the function @code{message}. As we have seen, @code{message} is an Emacs Lisp function especially designed for sending a one line message to a user. (@xref{message, , The @code{message} function}.) In summary, the @code{message} function prints its first argument in the echo area as is, except for occurrences of @samp{%d}, @samp{%s}, or @samp{%c}. When it sees one of these control sequences, the function looks to the second and subsequent arguments and prints the value of the argument in the location in the string where the control sequence is located. In the interactive @code{multiply-by-seven} function, the control string is @samp{%d}, which requires a number, and the value returned by evaluating @code{(* 7 5)} is the number 35. Consequently, the number 35 is printed in place of the @samp{%d} and the message is @samp{The result is 35}. (Note that when you call the function @code{multiply-by-seven}, the message is printed without quotes, but when you call @code{message}, the text is printed in double quotes. This is because the value returned by @code{message} is what appears in the echo area when you evaluate an expression whose first element is @code{message}; but when embedded in a function, @code{message} prints the text as a side effect without quotes.) @node Interactive Options, Permanent Installation, Interactive, Writing Defuns @comment node-name, next, previous, up @section Different Options for @code{interactive} @cindex Options for @code{interactive} @cindex Interactive options In the example, @code{multiply-by-seven} used @code{"p"} as the argument to @code{interactive}. This argument told Emacs to interpret your typing either @kbd{C-u} followed by a number or @key{META} followed by a number as a command to pass that number to the function as its argument. Emacs has more than twenty characters predefined for use with @code{interactive}. In almost every case, one or other of these options will enable you to pass the right information interactively to a function. (@xref{Interactive Codes, , Code Characters for @code{interactive}, elisp, The GNU Emacs Lisp Reference Manual}.) For example, the character @samp{r} causes Emacs to pass the beginning and end of the region (the current values of point and mark) to the function as two separate arguments. It is used as follows: @example (interactive "r") @end example On the other hand, a @samp{B} tells Emacs to ask for the name of a buffer that will be passed to the function. In this case, Emacs will ask for the name by prompting the user in the minibuffer, using a string that follows the @samp{B}, as in @code{"BAppend to buffer:@: "}. Not only will Emacs prompt for the name, but Emacs will complete the name if you type enough of it and press @key{TAB}. A function with two or more arguments can have information passed to each argument by adding parts to the string that follows @code{interactive}. When you do this, the information is passed to each argument in the same order it is specified in the @code{interactive} list. In the string, each part is separated from the next part by a @samp{\n}, which is a newline. For example, you could follow @code{"BAppend to buffer:@: "} with a @samp{\n}) and an @samp{r}. This would cause Emacs to pass the values of point and mark to the function as well as prompt you for the buffer---three arguments in all. In this case, the function definition would look like the following, where @code{buffer}, @code{start}, and @code{end} are the symbols to which @code{interactive} binds the buffer and the current values of the beginning and ending of the region: @example @group (defun @var{name-of-function} (buffer start end) "@var{documentation}@dots{}" (interactive "BAppend to buffer:@: \nr") @var{body-of-function}@dots{}) @end group @end example @noindent (The space after the colon in the prompt makes it look better when you are prompted. The @code{append-to-buffer} function looks exactly like this. @xref{append-to-buffer, , The Definition of @code{append-to-buffer}}.) If a function does not have arguments, then @code{interactive} does not require any. Such a function contains the simple expression @code{(interactive)}. The @code{mark-whole-buffer} function is like this. Alternatively, if the special letter-codes are not right for your application, you can pass your own arguments to @code{interactive} as a list. @xref{interactive, , Using @code{Interactive}, elisp, The GNU Emacs Lisp Reference Manual}, for more information about this advanced technique. @node Permanent Installation, let, Interactive Options, Writing Defuns @comment node-name, next, previous, up @section Install Code Permanently @cindex Install code permanently @cindex Permanent code installation @cindex Code installation When you install a function definition by evaluating it, it will stay installed until you quit Emacs. The next time you start a new session of Emacs, the function will not be installed unless you evaluate the function definition again. At some point, you may want to have code installed automatically whenever you start a new session of Emacs. There are several ways of doing this: @itemize @bullet @item If you have code that is just for yourself, you can put the code for the function definition in your @file{.emacs} initialization file. When you start Emacs, your @file{.emacs} file is automatically evaluated and all the function definitions within it are installed. @xref{Emacs Initialization, , Your @file{.emacs} File}. @item Alternatively, you can put the function definitions that you want installed in one or more files of their own and use the @code{load} function to cause Emacs to evaluate and thereby install each of the functions in the files. @xref{Loading Files, , Loading Files}. @item On the other hand, if you have code that your whole site will use, it is usual to put it in a file called @file{site-init.el} that is loaded when Emacs is built. This makes the code available to everyone who uses your machine. (See the @file{INSTALL} file that is part of the Emacs distribution.) @end itemize Finally, if you have code that everyone who uses Emacs may want, you can post it on a computer network or send a copy to the Free Software Foundation. (When you do this, please put a copyleft notice on the code before posting it.) If you send a copy of your code to the Free Software Foundation, it may be included in the next release of Emacs. In large part, this is how Emacs has grown over the past years, by donations. @node let, if, Permanent Installation, Writing Defuns @comment node-name, next, previous, up @section @code{let} @findex let The @code{let} expression is a special form in Lisp that you will need to use in most function definitions. Because it is so common, @code{let} will be described in this section. @code{let} is used to attach or bind a symbol to a value in such a way that the Lisp interpreter will not confuse the variable with a variable of the same name that is not part of the function. To understand why this special form is necessary, consider the situation in which you own a home that you generally refer to as `the house', as in the sentence, ``The house needs painting.'' If you are visiting a friend and your host refers to `the house', he is likely to be referring to @emph{his} house, not yours, that is, to a different house. If he is referring to his house and you think he is referring to your house, you may be in for some confusion. The same thing could happen in Lisp if a variable that is used inside of one function has the same name as a variable that is used inside of another function, and the two are not intended to refer to the same value. @cindex @samp{local variable} defined The @code{let} special form prevents this kind of confusion. @code{let} creates a name for a @dfn{local variable} that overshadows any use of the same name outside the @code{let} expression. This is like understanding that whenever your host refers to `the house', he means his house, not yours. (Symbols used in argument lists work the same way. @xref{defun, , The @code{defun} Special Form}.) Local variables created by a @code{let} expression retain their value @emph{only} within the @code{let} expression itself (and within expressions called within the @code{let} expression); the local variables have no effect outside the @code{let} expression. @code{let} can create more than one variable at once. Also, @code{let} gives each variable it creates an initial value, either a value specified by you, or @code{nil}. (In the jargon, this is called `binding the variable to the value'.) After @code{let} has created and bound the variables, it executes the code in the body of the @code{let}, and returns the value of the last expression in the body, as the value of the whole @code{let} expression. (`Execute' is a jargon term that means to evaluate a list; it comes from the use of the word meaning `to give practical effect to' (@cite{Oxford English Dictionary}). Since you evaluate an expression to perform an action, `execute' has evolved as a synonym to `evaluate'.) @menu * Parts of let Expression:: * Sample let Expression:: * Uninitialized let Variables:: @end menu @node Parts of let Expression, Sample let Expression, let, let @comment node-name, next, previous, up @subsection The Parts of a @code{let} Expression @cindex @code{let} expression, parts of @cindex Parts of @code{let} expression @cindex @samp{varlist} defined A @code{let} expression is a list of three parts. The first part is the symbol @code{let}. The second part is a list, called a @dfn{varlist}, each element of which is either a symbol by itself or a two-element list, the first element of which is a symbol. The third part of the @code{let} expression is the body of the @code{let}. The body usually consists of one or more lists. A template for a @code{let} expression looks like this: @example (let @var{varlist} @var{body}@dots{}) @end example @noindent The symbols in the varlist are the variables that are given initial values by the @code{let} special form. Symbols by themselves are given the initial value of @code{nil}; and each symbol that is the first element of a two-element list is bound to the value that is returned when the Lisp interpreter evaluates the second element. Thus, a varlist might look like this: @code{(thread (needles 3))}. In this case, in a @code{let} expression, Emacs binds the symbol @code{thread} to an initial value of @code{nil}, and binds the symbol @code{needles} to an initial value of 3. When you write a @code{let} expression, what you do is put the appropriate expressions in the slots of the @code{let} expression template. If the varlist is composed of two-element lists, as is often the case, the template for the @code{let} expression looks like this: @example @group (let ((@var{variable} @var{value}) (@var{variable} @var{value}) @dots{}) @var{body}@dots{}) @end group @end example @node Sample let Expression, Uninitialized let Variables, Parts of let Expression, let @comment node-name, next, previous, up @subsection Sample @code{let} Expression @cindex Sample @code{let} expression @cindex @code{let} expression sample The following expression creates and gives initial values to the two variables @code{zebra} and @code{tiger}. The body of the @code{let} expression is a list which calls the @code{message} function. @example @group (let ((zebra 'stripes) (tiger 'fierce)) (message "One kind of animal has %s and another is %s." zebra tiger)) @end group @end example Here, the varlist is @code{((zebra 'stripes) (tiger 'fierce))}. The two variables are @code{zebra} and @code{tiger}. Each variable is the first element of a two-element list and each value is the second element of its two-element list. In the varlist, Emacs binds the variable @code{zebra} to the value @code{stripes}, and binds the variable @code{tiger} to the value @code{fierce}. In this case, both values are symbols preceded by a quote. The values could just as well have been another list or a string. The body of the @code{let} follows after the list holding the variables. In this case, the body is a list that uses the @code{message} function to print a string in the echo area. You may evaluate the example in the usual fashion, by placing the cursor after the last parenthesis and typing @kbd{C-x C-e}. When you do this, the following will appear in the echo area: @example "One kind of animal has stripes and another is fierce." @end example As we have seen before, the @code{message} function prints its first argument, except for @samp{%s}. In this case, the value of the variable @code{zebra} is printed at the location of the first @samp{%s} and the value of the variable @code{tiger} is printed at the location of the second @samp{%s}. @node Uninitialized let Variables, , Sample let Expression, let @comment node-name, next, previous, up @subsection Uninitialized Variables in a @code{let} Statement @cindex Uninitialized @code{let} variables @cindex @code{let} variables uninitialized If you do not bind the variables in a @code{let} statement to specific initial values, they will automatically be bound to an initial value of @code{nil}, as in the following expression: @example @group (let ((birch 3) pine fir (oak 'some)) (message "Here are %d variables with %s, %s, and %s value." birch pine fir oak)) @end group @end example @noindent Here, the varlist is @code{((birch 3) pine fir (oak 'some))}. If you evaluate this expression in the usual way, the following will appear in your echo area: @example "Here are 3 variables with nil, nil, and some value." @end example @noindent In this case, Emacs binds the symbol @code{birch} to the number 3, binds the symbols @code{pine} and @code{fir} to @code{nil}, and binds the symbol @code{oak} to the value @code{some}. Note that in the first part of the @code{let}, the variables @code{pine} and @code{fir} stand alone as atoms that are not surrounded by parentheses; this is because they are being bound to @code{nil}, the empty list. But @code{oak} is bound to @code{some} and so is a part of the list @code{(oak 'some)}. Similarly, @code{birch} is bound to the number 3 and so is in a list with that number. (Since a number evaluates to itself, the number does not need to be quoted. Also, the number is printed in the message using a @samp{%d} rather than a @samp{%s}.) The four variables as a group are put into a list to delimit them from the body of the @code{let}. @node if, else, let, Writing Defuns @comment node-name, next, previous, up @section The @code{if} Special Form @findex if @cindex Conditional with @code{if} A third special form, in addition to @code{defun} and @code{let}, is the conditional @code{if}. This form is used to instruct the computer to make decisions. You can write function definitions without using @code{if}, but it is used often enough, and is important enough, to be included here. It is used, for example, in the code for the function @code{beginning-of-buffer}. The basic idea behind an @code{if}, is that ``@emph{if} a test is true, @emph{then} an expression is evaluated.'' If the test is not true, the expression is not evaluated. For example, you might make a decision such as, ``if it is warm and sunny, then go to the beach!'' @cindex @samp{if-part} defined @cindex @samp{then-part} defined An @code{if} expression written in Lisp does not use the word `then'; the test and the action are the second and third elements of the list whose first element is @code{if}. Nonetheless, the test part of an @code{if} expression is often called the @dfn{if-part} and the second argument is often called the @dfn{then-part}. Also, when an @code{if} expression is written, the true-or-false-test is usually written on the same line as the symbol @code{if}, but the action to carry out if the test is true, the ``then-part'', is written on the second and subsequent lines. This makes the @code{if} expression easier to read. @example @group (if @var{true-or-false-test} @var{action-to-carry-out-if-test-is-true}) @end group @end example @noindent The true-or-false-test will be an expression that is evaluated by the Lisp interpreter. Here is an example that you can evaluate in the usual manner. The test is whether the number 5 is greater than the number 4. Since it is, the message @samp{5 is greater than 4!} will be printed. @example @group (if (> 5 4) ; @r{if-part} (message "5 is greater than 4!")) ; @r{then-part} @end group @end example @noindent (The function @code{>} tests whether its first argument is greater than its second argument and returns true if it is.) @findex > (greater than) Of course, in actual use, the test in an @code{if} expression will not be fixed for all time as it is by the expression @code{(> 5 4)}. Instead, at least one of the variables used in the test will be bound to a value that is not known ahead of time. (If the value were known ahead of time, we would not need to run the test!) For example, the value may be bound to an argument of a function definition. In the following function definition, the character of the animal is a value that is passed to the function. If the value bound to @code{characteristic} is @code{fierce}, then the message, @samp{It's a tiger!} will be printed; otherwise, @code{nil} will be returned. @example @group (defun type-of-animal (characteristic) "Print message in echo area depending on CHARACTERISTIC. If the CHARACTERISTIC is the symbol `fierce', then warn of a tiger." (if (equal characteristic 'fierce) (message "It's a tiger!"))) @end group @end example @noindent If you are reading this inside of GNU Emacs, you can evaluate the function definition in the usual way to install it in Emacs, and then you can evaluate the following two expressions to see the results: @example @group (type-of-animal 'fierce) (type-of-animal 'zebra) @end group @end example @c Following sentences rewritten to prevent overfull hbox. @noindent When you evaluate @code{(type-of-animal 'fierce)}, you will see the following message printed in the echo area: @code{"It's a tiger!"}; and when you evaluate @code{(type-of-animal 'zebra)} you will see @code{nil} printed in the echo area. @menu * type-of-animal in detail:: An example of an @code{if} expression. @end menu @node type-of-animal in detail, , if, if @comment node-name, next, previous, up @subsection The @code{type-of-animal} Function in Detail Let's look at the @code{type-of-animal} function in detail. The function definition for @code{type-of-animal} was written by filling the slots of two templates, one for a function definition as a whole, and a second for an @code{if} expression. The template for every function that is not interactive is: @example @group (defun @var{name-of-function} (@var{argument-list}) "@var{documentation}@dots{}" @var{body}@dots{}) @end group @end example The parts of the function that match this template look like this: @example @group (defun type-of-animal (characteristic) "Print message in echo area depending on CHARACTERISTIC. If the CHARACTERISTIC is the symbol `fierce', then warn of a tiger." @var{body: the} @code{if} @var{expression}) @end group @end example In this case, the name of function is @code{type-of-animal}; it is passed the value of one argument. The argument list is followed by a multi-line documentation string. The documentation string is included in the example because it is a good habit to write documentation string for every function definition. The body of the function definition consists of the @code{if} expression. The template for an @code{if} expression looks like this: @example @group (if @var{true-or-false-test} @var{action-to-carry-out-if-the-test-returns-true}) @end group @end example In the @code{type-of-animal} function, the actual code for the @code{if} looks like this: @example @group (if (equal characteristic 'fierce) (message "It's a tiger!"))) @end group @end example Here, the true-or-false-test is the expression: @example (equal characteristic 'fierce) @end example @noindent In Lisp, @code{equal} is a function that determines whether its first argument is equal to its second argument. The second argument is the quoted symbol @code{'fierce} and the first argument is the value of the symbol @code{characteristic}---in other words, the argument passed to this function. In the first exercise of @code{type-of-animal}, the argument @code{fierce} is passed to @code{type-of-animal}. Since @code{fierce} is equal to @code{fierce}, the expression, @code{(equal characteristic 'fierce)}, returns a value of true. When this happens, the @code{if} evaluates the second argument or then-part of the @code{if}: @code{(message "It's tiger!")}. On the other hand, in the second exercise of @code{type-of-animal}, the argument @code{zebra} is passed to @code{type-of-animal}. @code{zebra} is not equal to @code{fierce}, so the then-part is not evaluated and @code{nil} is returned by the @code{if} expression. @node else, Truth & Falsehood, if, Writing Defuns @comment node-name, next, previous, up @section If--then--else Expressions @cindex Else An @code{if} expression may have an optional third argument, called the @dfn{else-part}, for the case when the true-or-false-test returns false. When this happens, the second argument or then-part of the overall @code{if} expression is @emph{not} evaluated, but the third or else-part @emph{is} evaluated. You might think of this as the cloudy day alternative for the decision `if it is warm and sunny, then go to the beach, else read a book!''. The word ``else'' is not written in the Lisp code; the else-part of an @code{if} expression comes after the then-part. In the written Lisp, the else-part is usually written to start on a line of its own and is indented less than the then-part: @example @group (if @var{true-or-false-test} @var{action-to-carry-out-if-the-test-returns-true}) @var{action-to-carry-out-if-the-test-returns-false}) @end group @end example For example, the following @code{if} expression prints the message @samp{4 is not greater than 5!} when you evaluate it in the usual way: @example @group (if (> 4 5) ; @r{if-part} (message "5 is greater than 4!") ; @r{then-part} (message "4 is not greater than 5!")) ; @r{else-part} @end group @end example @noindent Note that the different levels of indentation make it easy to distinguish the then-part from the else-part. (GNU Emacs has several commands that automatically indent @code{if} expressions correctly. @xref{Typing Lists, , GNU Emacs Helps You Type Lists}.) We can extend the @code{type-of-animal} function to include an else-part by simply incorporating an additional part to the @code{if} expression. You can see the consequences of doing this if you evaluate the following version of the @code{type-of-animal} function definition to install it and then evaluate the two subsequent expressions to pass different arguments to the function. @example @group (defun type-of-animal (characteristic) ; @r{Second version.} "Print message in echo area depending on CHARACTERISTIC. If the CHARACTERISTIC is the symbol `fierce', then warn of a tiger; else say it's not fierce." (if (equal characteristic 'fierce) (message "It's a tiger!") (message "It's not fierce!"))) @end group @end example @sp 1 @example (type-of-animal 'fierce) (type-of-animal 'zebra) @end example @c Following sentence rewritten to prevent overfull hbox. @noindent When you evaluate @code{(type-of-animal 'fierce)}, you will see the following message printed in the echo area: @code{"It's a tiger!"}; but when you evaluate @code{(type-of-animal 'zebra)}, you will see @code{"It's not fierce!"}. (Of course, if the @var{characteristic} were @code{ferocious}, the message @code{"It's not fierce!"} would be printed; and it would be misleading! When you write code, you need to take into account the possibility that some such argument will be tested by the @code{if} and write your program accordingly.) @node Truth & Falsehood, save-excursion, else, Writing Defuns @comment node-name, next, previous, up @section Truth and Falsehood in Lisp @cindex Truth and falsehood in Lisp @cindex Falsehood and truth in Lisp @findex nil There is an important aspect to the truth test in an @code{if} expression. So far, we have spoken of `true' and `false' as values of predicates as if they were new kinds of Lisp objects. In fact, `false' is just our old friend @code{nil}. Anything else---anything at all---is `true'. The expression that tests for truth is interpreted as @dfn{true} if the result of evaluating it is a value that is not @code{nil}. In other words, the result of the test is considered true if the value returned is a number such as 47, a string such as @code{"hello"}, or a symbol (other than @code{nil}) such as @code{flowers}, or a list, or even a buffer! Before illustrating this, we need an explanation of @code{nil}. In Lisp, the symbol @code{nil} has two meanings. First, it means the empty list. Second, it means false and is the value returned when a true-or-false-test tests false. @code{nil} can be written as an empty list, @code{()}, or as @code{nil}. As far as the Lisp interpreter is concerned, @code{()} and @code{nil} are the same. Humans, however, tend to use @code{nil} for false and @code{()} for the empty list. In Lisp, any value that is not @code{nil}---is not the empty list---is considered true. This means that if an evaluation returns something that is not an empty list, an @code{if} expression will test true. For example, if a number is put in the slot for the test, it will be evaluated and will return itself, since that is what numbers do when evaluated. In this case, the @code{if} expression will test true. The expression tests false only when @code{nil}, an empty list, is returned by evaluating the expression. You can see this by evaluating the two expressions in the following examples. In the first example, the number 4 is evaluated as the test in the @code{if} expression and returns itself; consequently, the then-part of the expression is evaluated and returned: @samp{true} appears in the echo area. In the second example, the @code{nil} indicates false; consequently, the else-part of the expression is evaluated and returned: @samp{false} appears in the echo area. @example @group (if 4 'true 'false) @end group @group (if nil 'true 'false) @end group @end example Incidentally, if some other useful value is not available for a test that returns true, then the Lisp interpreter will return the symbol @code{t} for true. For example, the expression @code{(> 5 4)} returns @code{t} when evaluated, as you can see by evaluating it in the usual way: @example (> 5 4) @end example @noindent On the other hand, this function returns @code{nil} if the test is false. @example (> 4 5) @end example @node save-excursion, Review, Truth & Falsehood, Writing Defuns @comment node-name, next, previous, up @section @code{save-excursion} @findex save-excursion @cindex Region, what it is @cindex Preserving point, mark, and buffer @cindex Point, mark, buffer preservation @findex point @findex mark The @code{save-excursion} function is the fourth and final special form that we will discuss in this chapter. In Emacs Lisp programs used for editing, the @code{save-excursion} function is very common. It saves the location of point and mark, executes the body of the function, and then restores point and mark to their previous positions if their locations were changed. Its primary purpose is to keep the user from being surprised and disturbed by unexpected movement of point or mark. Before discussing @code{save-excursion}, however, it may be useful first to review what point and mark are in GNU Emacs. @dfn{Point} is the current location of the cursor. Wherever the cursor is, that is point. More precisely, on terminals where the cursor appears to be on top of a character, point is immediately before the character. In Emacs Lisp, point is an integer. The first character in a buffer is number one, the second is number two, and so on. The function @code{point} returns the current position of the cursor as a number. Each buffer has its own value for point. The @dfn{mark} is another position in the buffer; its value can be set with a command such as @kbd{C-@key{SPC}} (@code{set-mark-command}). If a mark has been set, you can use the command @kbd{C-x C-x} (@code{exchange-point-and-mark}) to cause the cursor to jump to the mark and set the mark to be the previous position of point. In addition, if you set another mark, the position of the previous mark is saved in the mark ring. Many mark positions can be saved this way. You can jump the cursor to a saved mark by typing @kbd{C-u C-@key{SPC}} one or more times. The part of the buffer between point and mark is called @dfn{the region}. Numerous commands work on the region, including @code{center-region}, @code{count-lines-region}, @code{kill-region}, and @code{print-region}. The @code{save-excursion} special form saves the locations of point and mark and restores those positions after the code within the body of the special form is evaluated by the Lisp interpreter. Thus, if point were in the beginning of a piece of text and some code moved point to the end of the buffer, the @code{save-excursion} would put point back to where it was before, after the expressions in the body of the function were evaluated. In Emacs, a function frequently moves point as part of its internal workings even though a user would not expect this. For example, @code{count-lines-region} moves point. To prevent the user from being bothered by jumps that are both unexpected and (from the user's point of view) unnecessary, @code{save-excursion} is often used to keep point and mark in the location expected by the user. The use of @code{save-excursion} is good housekeeping. To make sure the house stays clean, @code{save-excursion} restores the values of point and mark even if something goes wrong in the code inside of it (or, to be more precise and to use the proper jargon, ``in case of abnormal exit''). This feature is very helpful. In addition to recording the values of point and mark, @code{save-excursion} keeps track of the current buffer, and restores it, too. This means you can write code that will change the buffer and have @code{save-excursion} switch you back to the original buffer. This is how @code{save-excursion} is used in @code{append-to-buffer}. (@xref{append-to-buffer, , The Definition of @code{append-to-buffer}}.) @menu * Template for save-excursion:: One slot to fill in. @end menu @node Template for save-excursion, , save-excursion, save-excursion @comment node-name, next, previous, up @subsection Template for a @code{save-excursion} Expression The template for code using @code{save-excursion} is simple: @example @group (save-excursion @var{body}@dots{}) @end group @end example @noindent The body of the function is one or more expressions that will be evaluated in sequence by the Lisp interpreter. If there is more than one expression in the body, the value of the last one will be returned as the value of the @code{save-excursion} function. The other expressions in the body are evaluated only for their side effects; and @code{save-excursion} itself is used only for its side effect (which is restoring the positions of point and mark). In more detail, the template for a @code{save-excursion} expression looks like this: @example @group (save-excursion @var{first-expression-in-body} @var{second-expression-in-body} @var{third-expression-in-body} @dots{} @var{last-expression-in-body}) @end group @end example @noindent An expression, of course, may be a symbol on its own or a list. In Emacs Lisp code, a @code{save-excursion} expression often occurs within the body of a @code{let} expression. It looks like this: @example @group (let @var{varlist} (save-excursion @var{body}@dots{})) @end group @end example @node Review, defun Exercises, save-excursion, Writing Defuns @comment node-name, next, previous, up @section Review In the last few chapters we have introduced a fair number of functions and special forms. Here they are described in brief, along with a few similar functions that have not been mentioned yet. @table @code @item eval-last-sexp Evaluate the last symbolic expression before the current location of point. The value is printed in the echo area unless the function is invoked with an argument; in that case, the output is printed in the current buffer. This command is normally bound to @kbd{C-x C-e}. @item defun Define function. This special form has up to five parts: the name, a template for the arguments that will be passed the function, documentation, an optional interactive declaration, and the body of the definition. @need 1250 For example: @example @group (defun back-to-indentation () "Point to first visible character on line." (interactive) (beginning-of-line 1) (skip-chars-forward " \t")) @end group @end example @item interactive Declare to the interpreter that the function can be used interactively. This special form may be followed by a string with one or more parts that pass the information to the arguments of the function, in sequence. These parts may also tell the interpreter to prompt for information. Parts of the string are separated by newlines, @samp{\n}. Common code characters are: @table @code @item b The name of an existing buffer. @item f The name of an existing file. @item p The numeric prefix argument. (Note that this `p' is lower case.) @item r Point and the mark, as two numeric arguments, smallest first. This is the only code letter that specifies two successive arguments rather than one. @end table @xref{Interactive Codes, , Code Characters for @samp{interactive}, elisp, The GNU Emacs Lisp Reference Manual}, for a complete list of code characters. @item let Declare that a list of variables is for use within the body of the @code{let} and give them an initial value, either @code{nil} or a specified value; then evaluate the rest of the expressions in the body of the @code{let} and return the value of the last one. Inside the body of the @code{let}, the Lisp interpreter does not see the values of the variables of the same names that are bound outside of the @code{let}. @need 1250 For example, @example @group (let ((foo (buffer-name)) (bar (buffer-size))) (message "This buffer is %s and has %d characters." foo bar)) @end group @end example @item save-excursion Record the values of point and mark and the current buffer before evaluating the body of this special form. Restore the values of point and mark and buffer afterward. @need 1250 For example, @example @group (message "We are %d characters into this buffer." (- (point) (save-excursion (goto-char (point-min)) (point)))) @end group @end example @item if Evaluate the first argument to the function; if it is true, evaluate the second argument; else evaluate the third argument, if there is one. The @code{if} special form is called a @dfn{conditional}. There are other conditionals in Emacs Lisp, but @code{if} is perhaps the most commonly used. @need 1250 For example, @example @group (if (string= (int-to-string 19) (substring (emacs-version) 10 12)) (message "This is version 19 Emacs") (message "This is not version 19 Emacs")) @end group @end example @item equal @itemx eq Test whether two objects are the same. @code{equal} returns true if the two objects have a similar structure and contents. Another function, @code{eq}, returns true if both arguments are actually the same object. @findex equal @findex eq @need 1250 @item < @itemx > @itemx <= @itemx >= The @code{<} function tests whether the first argument is smaller than the second argument. A corresponding function, @code{>}, tests whether the first argument is greater than the second. Likewise, @code{<=} tests whether the first argument is less than or equal to the second and @code{>=} tests whether the first argument is greater than or equal to the second. In all cases, both arguments must be numbers. @item message Print a message in the echo area. The message can be only one line long. The first argument is a string that can contain @samp{%s}, @samp{%d}, or @samp{%c} to print the value of arguments that follow the string. The argument used by @samp{%s} must be a string or a symbol; the argument used by @samp{%d} must be a number. The argument used by @samp{%c} must be a number; it will be printed as the character with that @sc{ascii} code. @item setq @itemx set The @code{setq} function sets the value of its first argument to the value of the second argument. The first argument is automatically quoted by @code{setq}. It does the same for succeeding pairs of arguments. Another function, @code{set}, takes only two arguments and evaluates both of them before setting the value returned by its first argument to the value returned by its second argument. @item buffer-name Without an argument, return the name of the buffer, as a string. @itemx buffer-file-name Without an argument, return the name of the file the buffer is visiting. @item current-buffer Return the buffer in which Emacs is active; it may not be the buffer that is visible on the screen. @item other-buffer Return the most recently selected buffer (other than the buffer passed to @code{other-buffer} as an argument and other than the current buffer). @item switch-to-buffer Select a buffer for Emacs to be active in and display it in the current window so users can look at it. Usually bound to @kbd{C-x b}. @item set-buffer Switch Emacs's attention to a buffer on which programs will run. Don't alter what the window is showing. @item buffer-size Return the number of characters in the current buffer. @item point Return the value of the current position of the cursor, as an integer counting the number of characters from the beginning of the buffer. @item point-min Return the minimum permissible value of point in the current buffer. This is 1, unless narrowing is in effect. @item point-max Return the value of the maximum permissible value of point in the current buffer. This is the end of the buffer, unless narrowing is in effect. @end table @need 1500 @node defun Exercises, , Review, Writing Defuns @section Exercises @itemize @bullet @item Write a non-interactive function that doubles the value of its argument, a number. Make that function interactive. @item Write a function that tests whether the current value of @code{fill-column} is greater than the argument passed the function, and if so, prints an appropriate message. @end itemize @node Buffer Walk Through, More Complex, Writing Defuns, Top @comment node-name, next, previous, up @chapter A Few Buffer--Related Functions In this chapter we study in detail several of the functions used in GNU Emacs. This is called a ``walk-through''. These functions are used as examples of Lisp code, but are not imaginary examples; with the exception of the first, simplified function definition, these functions show the actual code used in GNU Emacs. You can learn a great deal from these definitions. The functions described here are all related to buffers. Later, we will study other functions. @menu * Finding More:: How to find more information. * simplified-beginning-of-buffer:: Shows @code{goto-char}, @code{point-min}, and @code{push-mark}. * mark-whole-buffer:: Almost the same as @code{beginning-of-buffer}. * append-to-buffer:: Uses @code{save-excursion} and @code{insert-buffer-substring}. * Buffer Related Review:: Review. * Buffer Exercises:: @end menu @node Finding More, simplified-beginning-of-buffer, Buffer Walk Through, Buffer Walk Through @section Finding More Information @findex describe-function, @r{introduced} @cindex Find function documentation In this walk-through, I will describe each new function as we come to it, sometimes in detail and sometimes briefly. If you are interested, you can get the full documentation of any Emacs Lisp function at any time by typing @kbd{C-h f} and then the name of the function (and then @key{RET}). Similarly, you can get the full documentation for a variable by typing @kbd{C-h v} and then the name of the variable (and then @key{RET}). @cindex Find source of function Also, if you want to see a function in its original source file, you can use the @code{find-tags} function to jump to it. Type @kbd{M-.} (i.e., type the @key{META} and the period key at the same time, or else type the @key{ESC} key and then type the period key), and then, at the prompt, type in the name of the function whose source code you want to see, such as @code{mark-whole-buffer}, and then type @key{RET}. Emacs will switch buffers and display the source code for the function on your screen. To switch back to this buffer, type @kbd{C-x b @key{RET}}. @cindex TAGS table, specifying @findex find-tags Depending on how the initial default values of your copy of Emacs are set, you may also need to specify a `tags table', which is a file called @file{TAGS}. The one you will most likely want to specify is in the @file{emacs/src} directory; thus you would use the @code{M-x visit-tags-table} command and specify a pathname such as @file{/usr/local/lib/emacs/19.23/src/TAGS}. @xref{Tags, , Tag Tables, emacs, The GNU Emacs Manual}. Also, see @ref{etags, , Create Your Own @file{TAGS} File}, for how to create your own. After you become more familiar with Emacs Lisp, you will find that you will frequently use @code{find-tags} to navigate your way around source code; and you will create your own @file{TAGS} tables. @cindex Library, as term for `file' Incidentally, the files that contain Lisp code are conventionally called @dfn{libraries}. The metaphor is derived from that of a specialized library, such as a law library or an engineering library, rather than a general library. Each library, or file, contains functions that relate to a particular topic or activity, such as @file{abbrev.el} for handling abbreviations and other typing shortcuts, and @file{help.el} for on-line help. (Sometimes several libraries provide code for a single activity, as the various @file{rmail@dots{}} files provide code for reading electronic mail.) In @cite{The GNU Emacs Manual}, you will see sentences such as ``The @kbd{C-h p} command lets you search the standard Emacs Lisp libraries by topic keywords.'' @node simplified-beginning-of-buffer, mark-whole-buffer, Finding More, Buffer Walk Through @comment node-name, next, previous, up @section A Simplified @code{beginning-of-buffer} Definition @findex simplified-beginning-of-buffer The @code{beginning-of-buffer} command is a good function to start with since you are likely to be familiar with it and it is easy to understand. Used as an interactive command, @code{beginning-of-buffer} moves the cursor to the beginning of the buffer, leaving the mark at the previous position. It is generally bound to @kbd{M-<}. In this section, we will discuss a shortened version of the function that shows how it is most frequently used. This shortened function works as written, but it does not contain the code for a complex option. In another section, we will describe the entire function. (@xref{beginning-of-buffer, , Complete Definition of @code{beginning-of-buffer}}.) Before looking at the code, let's consider what the function definition has to contain: it must include an expression that makes the function interactive so it can be called by typing @kbd{M-x beginning-of-buffer} or by typing a keychord such as @kbd{C-<}; it must include code to leave a mark at the original position in the buffer; and it must include code to move the cursor to the beginning of the buffer. Here is the complete text of the shortened version of the function: @example @group (defun simplified-beginning-of-buffer () "Move point to the beginning of the buffer; leave mark at previous position." (interactive) (push-mark) (goto-char (point-min))) @end group @end example Like all function definitions, this definition has five parts following the special form @code{defun}: @enumerate @item The name: in this case, @code{simplified-beginning-of-buffer}. @item A list of the arguments: in this case, an empty list, @code{()}, @item The documentation string. @item The interactive expression. @item The body. @end enumerate @noindent In this function definition, the argument list is empty; this means that this function does not require any arguments. (When we look at the definition for the complete function, we will see that it may be passed an optional argument.) The interactive expression tells Emacs that the function is intended to be used interactively. In this case, @code{interactive} does not have an argument because @code{simplified-beginning-of-buffer} does not require one. The body of the function consists of the two lines: @example @group (push-mark) (goto-char (point-min)) @end group @end example The first of these lines is the expression, @code{(push-mark)}. When this expression is evaluated by the Lisp interpreter, it sets a mark at the current position of the cursor, wherever that may be. The position of this mark is saved in the mark ring. The next line is @code{(goto-char (point-min))}. This expression jumps the cursor to the minimum point in the buffer, that is, to the beginning of the buffer (or to the beginning of the accessible portion of the buffer if it is narrowed. @xref{Narrowing & Widening, , Narrowing and Widening}.) The @code{push-mark} command sets a mark at the place where the cursor was located before it was moved to the beginning of the buffer by the @code{(goto-char (point-min))} expression. Consequently, you can, if you wish, go back to where you were originally by typing @kbd{C-x C-x}. That is all there is to the function definition! @findex describe-function When you are reading code such as this and come upon an unfamiliar function, such as @code{goto-char}, you can find out what it does by using the @code{describe-function} command. To use this command, type @kbd{C-h f} and then type in the name of the function and press @key{RET}. The @code{describe-function} command will print the function's documentation string in a @file{*Help*} window. For example, the documentation for @code{goto-char} is: @example @group One arg, a number. Set point to that number. Beginning of buffer is position (point-min), end is (point-max). @end group @end example @noindent (The prompt for @code{describe-function} will offer you the symbol preceding the cursor, so you can save typing by positioning the cursor right after the function and then typing @kbd{C-h f @key{RET}}.) The @code{end-of-buffer} function definition is written in the same way as the @code{beginning-of-buffer} definition except that the body of the function contains the expression @code{(goto-char (point-max))} in place of @code{(goto-char (point-min))}. @node mark-whole-buffer, append-to-buffer, simplified-beginning-of-buffer, Buffer Walk Through @comment node-name, next, previous, up @section The Definition of @code{mark-whole-buffer} @findex mark-whole-buffer The @code{mark-whole-buffer} function is no harder to understand than the @code{simplified-beginning-of-buffer} function. In this case, however, we will look at the complete function, not a shortened version. The @code{mark-whole-buffer} function is not as commonly used as the @code{beginning-of-buffer} function, but is useful nonetheless: it marks a whole buffer as a region by putting point at the beginning and a mark at the end of the buffer. It is generally bound to @kbd{C-x h}. @need 1250 The code for the complete function looks like this: @example @group (defun mark-whole-buffer () "Put point at beginning and mark at end of buffer." (interactive) (push-mark (point)) (push-mark (point-max)) (goto-char (point-min))) @end group @end example Like all other functions, the @code{mark-whole-buffer} function fits into the template for a function definition. The template looks like this: @example @group (defun @var{name-of-function} (@var{argument-list}) "@var{documentation}@dots{}" (@var{interactive-expression}@dots{}) @var{body}@dots{}) @end group @end example Here is how the function works: the name of the function is @code{mark-whole-buffer}; it is followed by an empty argument list, @samp{()}, which means that the function does not require arguments. The documentation comes next. The next line is an @code{(interactive)} expression that tells Emacs that the function will be used interactively. These details are similar to the @code{simplified-beginning-of-buffer} function described in the previous section. @menu * Body of mark-whole-buffer:: Only three lines of code. @end menu @node Body of mark-whole-buffer, , mark-whole-buffer, mark-whole-buffer @comment node-name, next, previous, up @subsection Body of @code{mark-whole-buffer} The body of the @code{mark-whole-buffer} function consists of three lines of code: @example @group (push-mark (point)) (push-mark (point-max)) (goto-char (point-min)) @end group @end example The first of these lines is the expression, @code{(push-mark (point))}. This line does exactly the same job as the first line of the body of the @code{simplified-beginning-of-buffer} function, which is written @code{(push-mark)}. In both cases, the Lisp interpreter sets a mark at the current position of the cursor. I don't know why the expression in @code{mark-whole-buffer} is written @code{(push-mark (point))} and the expression in @code{beginning-of-buffer} is written @code{(push-mark)}. Perhaps whoever wrote the code did not know that the argument for @code{push-mark} is optional and that if @code{push-mark} is not passed an argument, the function automatically sets mark at the location of point by default. Or perhaps the expression was written so as to parallel the structure of the next line. In any case, the line causes Emacs to determine the position of point and set a mark there. The next line of @code{mark-whole-buffer} is @code{(push-mark (point-max))}. This expression sets a mark at the point in the buffer that has the highest number. This will be the end of the buffer (or, if the buffer is narrowed, the end of the accessible portion of the buffer. @xref{Narrowing & Widening, , Narrowing and Widening}, for more about narrowing.) After this mark has been set, the previous mark, the one set at point, is no longer set, but Emacs remembers its position, just as all other recent marks are always remembered. This means that you can, if you wish, go back to that position by typing @kbd{C-u C-@key{SPC}} twice. Finally, the last line of the function is @code{(goto-char (point-min)))}. This is written exactly the same way as it is written in @code{beginning-of-buffer}. The expression moves the cursor to the minimum point in the buffer, that is, to the beginning of the buffer (or to the beginning of the accessible portion of the buffer). As a result of this, point is placed at the beginning of the buffer and mark is set at the end of the buffer. The whole buffer is, therefore, the region. @node append-to-buffer, Buffer Related Review, mark-whole-buffer, Buffer Walk Through @comment node-name, next, previous, up @section The Definition of @code{append-to-buffer} @findex append-to-buffer The @code{append-to-buffer} command is very nearly as simple as the @code{mark-whole-buffer} command. What it does is copy the region (that is, the part of the buffer between point and mark) from the current buffer to a specified buffer. @findex insert-buffer-substring The @code{append-to-buffer} command uses the @code{insert-buffer-substring} function to copy the region. @code{insert-buffer-substring} is described by its name: it takes a string of characters from part of a buffer, a ``substring'', and inserts them into another buffer. Most of @code{append-to-buffer} is concerned with setting up the conditions for @code{insert-buffer-substring} to work: the code must specify both the buffer to which the text will go and the region that will be copied. Here is the complete text of the function: @example @group (defun append-to-buffer (buffer start end) "Append to specified buffer the text of the region. It is inserted into that buffer before its point. @end group @group When calling from a program, give three arguments: a buffer or the name of one, and two character numbers specifying the portion of the current buffer to be copied." (interactive "BAppend to buffer:@: \nr") (let ((oldbuf (current-buffer))) (save-excursion (set-buffer (get-buffer-create buffer)) (insert-buffer-substring oldbuf start end)))) @end group @end example The function can be understood by looking at it as a series of filled-in templates. The outermost template is for the function definition. In this case, it looks like this (with several slots filled in): @example @group (defun append-to-buffer (buffer start end) "@var{documentation}@dots{}" (interactive "BAppend to buffer:@: \nr") @var{body}@dots{}) @end group @end example The first line of the function includes its name and three arguments. The arguments are the @code{buffer} to which the text will be copied, and the @code{start} and @code{end} of the region in the current buffer that will be copied. The next part of the function is the documentation, which is clear and complete. @menu * append interactive:: A two part interactive expression. * append-to-buffer body:: Incorporates a @code{let} expression. * append save-excursion:: How the @code{save-excursion} works. @end menu @node append interactive, append-to-buffer body, append-to-buffer, append-to-buffer @comment node-name, next, previous, up @subsection The @code{append-to-buffer} Interactive Expression Since the @code{append-to-buffer} function will be used interactively, the function must have an @code{interactive} expression. (For a review of @code{interactive}, see @ref{Interactive, , Making a Function Interactive}.) The expression reads as follows: @example (interactive "BAppend to buffer:@: \nr") @end example @noindent This expression has an argument inside of quotation marks and that argument has two parts, separated by @samp{\n}. The first part is @samp{BAppend to buffer:@: }. Here, the @samp{B} tells Emacs to ask for the name of the buffer that will be passed to the function. Emacs will ask for the name by prompting the user in the minibuffer, using the string following the @samp{B}, which is the string @samp{Append to buffer:@: }. Emacs then binds the variable @code{buffer} in the function's argument list to the specified buffer. The newline, @samp{\n}, separates the first part of the argument from the second part. It is followed by an @samp{r} that tells Emacs to bind the two arguments that follow the symbol @code{buffer} in the function's argument list (that is, @code{start} and @code{end}) to the values of point and mark. @node append-to-buffer body, append save-excursion, append interactive, append-to-buffer @comment node-name, next, previous, up @subsection The Body of @code{append-to-buffer} The body of the @code{append-to-buffer} function begins with @code{let}. As we have seen before (@pxref{let, , @code{let}}), the purpose of a @code{let} expression is to create and give initial values to one or more variables that will only be used within the body of the @code{let}. This means that such a variable will not be confused with any variable of the same name outside the @code{let} expression. We can see how the @code{let} expression fits into the function as a whole by showing a template for @code{append-to-buffer} with the @code{let} expression in outline: @example @group (defun append-to-buffer (buffer start end) "@var{documentation}@dots{}" (interactive "BAppend to buffer:@: \nr") (let ((@var{variable} @var{value})) @var{body}@dots{}) @end group @end example The @code{let} expression has three elements: @enumerate @item The symbol @code{let}; @item A varlist containing, in this case, a single two-element list, @code{(@var{variable} @var{value})}; @item The body of the @code{let} expression. @end enumerate In the @code{append-to-buffer} function, the varlist looks like this: @example (oldbuf (current-buffer)) @end example @noindent In this part of the @code{let} expression, the one variable, @code{oldbuf}, is bound to the value returned by the @code{(current-buffer)} expression. The variable, @code{oldbuf}, is used to keep track of the buffer in which you are working. The element or elements of a varlist are surrounded by a set of parentheses so the Lisp interpreter can distinguish the varlist from the body of the @code{let}. As a consequence, the two-element list within the varlist is surrounded by circumscribing set of parentheses. The line looks like this: @example @group (let ((oldbuf (current-buffer))) @dots{} ) @end group @end example @noindent The two parentheses before @code{oldbuf} might surprise you if you did not realize that the first parenthesis before @code{oldbuf} marks the boundary of the varlist and the second parenthesis marks the beginning of the two-element list, @code{(oldbuf (current-buffer))}. @node append save-excursion, , append-to-buffer body, append-to-buffer @comment node-name, next, previous, up @subsection @code{save-excursion} in @code{append-to-buffer} The body of the @code{let} expression in @code{append-to-buffer} consists of a @code{save-excursion} expression. The @code{save-excursion} function saves the locations of point and mark, and restores them to those positions after the expressions in the body of the @code{save-excursion} complete execution. In addition, @code{save-excursion} keeps track of the original buffer, and restores it. This is how @code{save-excursion} is used in @code{append-to-buffer}. @cindex Indentation for formatting @cindex Formatting convention Incidentally, it is worth noting here that a Lisp function is normally formatted so that everything that is enclosed in a multi-line spread is indented more to the right than the first symbol. In this function definition, the @code{let} is indented more than the @code{defun}, and the @code{save-excursion} is indented more than the @code{let}, like this: @example @group (defun @dots{} @dots{} @dots{} (let@dots{} (save-excursion @dots{} @end group @end example @noindent This formatting convention makes it easy to see that the two lines in the body of the @code{save-excursion} are enclosed by the parentheses associated with @code{save-excursion}, just as the @code{save-excursion} itself is enclosed by the parentheses associated with the @code{let}: @example @group (let ((oldbuf (current-buffer))) (save-excursion (set-buffer (get-buffer-create buffer)) (insert-buffer-substring oldbuf start end)))) @end group @end example The use of the @code{save-excursion} function can be viewed as a process of filling in the slots of a template: @example @group (save-excursion @var{first-expression-in-body} @var{second-expression-in-body} @dots{} @var{last-expression-in-body}) @end group @end example @noindent In this function, the body of the @code{save-excursion} contains only two expressions. The body looks like this: @example @group (set-buffer (get-buffer-create buffer)) (insert-buffer-substring oldbuf start end) @end group @end example When the @code{append-to-buffer} function is evaluated, the two expressions in the body of the @code{save-excursion} are evaluated in sequence. The value of the last expression is returned as the value of the @code{save-excursion} function; the other expression is evaluated only for its side effects. The first line in the body of the @code{save-excursion} uses the @code{set-buffer} function to change the current buffer to the one specified in the first argument to @code{append-to-buffer}. (Changing the buffer is the side effect; as we have said before, in Lisp, a side effect is often the primary thing we want.) The second line does the primary work of the function. The @code{set-buffer} function changes Emacs' attention to the buffer to which the text will be copied and from which @code{save-excursion} will return. The line looks like this: @example (set-buffer (get-buffer-create buffer)) @end example The innermost expression of this list is @code{(get-buffer-create buffer)}. This expression uses the @code{get-buffer-create} function, which either gets the named buffer, or if it does not exist, creates one with the given name. This means you can use @code{append-to-buffer} to put text into a buffer that did not previously exist. @code{get-buffer-create} also keeps @code{set-buffer} from getting an unnecessary error: @code{set-buffer} needs a buffer to go to; if you were to specify a buffer that does not exist, Emacs would baulk. Since @code{get-buffer-create} will create a buffer if none exists, @code{set-buffer} is always provided with a buffer. The last line of @code{append-to-buffer} does the work of appending the text: @example (insert-buffer-substring oldbuf start end) @end example @noindent The @code{insert-buffer-substring} function copies a string @emph{from} the buffer specified as its first argument and inserts the string into the present buffer. In this case, the argument to @code{insert-buffer-substring} is the value of the variable created and bound by the @code{let}, namely the value of @code{oldbuf}, which was the current buffer when you gave the @code{append-to-buffer} command. After @code{insert-buffer-substring} has done its work, @code{save-excursion} will restore the action to the original buffer and @code{append-to-buffer} will have done its job. Written in skeletal form, the workings of the body look like this: @example @group (let (@var{bind-}@code{oldbuf}@var{-to-value-of-}@code{current-buffer}) (save-excursion ; @r{Keep track of buffer.} @var{change-buffer} @var{insert-substring-from-}@code{oldbuf}@var{-into-buffer}) @var{change-back-to-original-buffer-when-finished} @var{let-the-local-meaning-of-}@code{oldbuf}@var{-disappear-when-finished} @end group @end example In summary, @code{append-to-buffer} works as follows: it saves the value of the current buffer in the variable called @code{oldbuf}. It gets the new buffer, creating one if need be, and switches Emacs to it. Using the value of @code{oldbuf}, it inserts the region of text from the old buffer into the new buffer; and then using @code{save-excursion}, it brings you back to your original buffer. In looking at @code{append-to-buffer}, you have explored a fairly complex function. It shows how to use @code{let} and @code{save-excursion}, and how to change to and come back from another buffer. Many functions definitions use @code{let}, @code{save-excursion}, and @code{set-buffer} this way. @node Buffer Related Review, Buffer Exercises, append-to-buffer, Buffer Walk Through @comment node-name, next, previous, up @section Review Here is a brief summary of the various functions discussed in this chapter. @table @code @item describe-function @itemx describe-variable Print the documentation for a function or variable. Conventionally bound to @kbd{C-h f} and @kbd{C-h v}. @item find-tag Find the file containing the source for a function or variable and switch buffers to it, positioning point at the beginning of the item. Conventionally bound to @kbd{M-.} (that's a period following the @key{META} key). @item save-excursion Save the location of point and mark and restore their values after the arguments to @code{save-excursion} have been evaluated. Also, remember the current buffer and return to it. @item push-mark Set mark at a location and record the value of the previous mark on the mark ring. The mark is a location in the buffer that will keep its relative position even if text is added to or removed from the buffer. @item goto-char Set point to the location specified by the value of the argument, which can be a number, a marker, or an expression that returns the number of a position, such as @code{(point-min)}. @item insert-buffer-substring Copy a region of text from a buffer that is passed to the function as an argument and insert the region into the current buffer. @item mark-whole-buffer Mark the whole buffer as a region. Normally bound to @kbd{C-x h}. @item set-buffer Switch the attention of Emacs to another buffer, but do not change the window being displayed. Used when the program rather than a human is to work on a different buffer. @item get-buffer-create @itemx get-buffer Find a named buffer or create one if a buffer of that name does not exist. The @code{get-buffer} function returns @code{nil} if the named buffer does not exist. @end table @need 1500 @node Buffer Exercises, , Buffer Related Review, Buffer Walk Through @section Exercises @itemize @bullet @item Write your own @code{simplified-end-of-buffer} function definition; then test it to see whether it works. @item Use @code{if} and @code{get-buffer} to write a function that prints a message telling you whether a buffer exists. @item Using @code{find-tag}, find the source for the @code{copy-to-buffer} function. @end itemize @node More Complex, Narrowing & Widening, Buffer Walk Through, Top @comment node-name, next, previous, up @chapter A Few More Complex Functions In this chapter, we build on what we have learned in previous chapters by looking at more complex functions. The @code{copy-to-buffer} function illustrates use of two @code{save-excursion} expressions in one definition, while the @code{insert-buffer} function illustrates use of @key{*} in an @code{interactive} expression, use of @code{or}, and the important distinction between a name and the object to which the name refers. @menu * copy-to-buffer:: With @code{set-buffer}, @code{get-buffer-create}. * insert-buffer:: Read-only, and with @code{or}. * beginning-of-buffer:: Shows @code{goto-char}, @code{point-min}, and @code{push-mark}. * Second Buffer Related Review:: * &optional Exercise :: @end menu @node copy-to-buffer, insert-buffer, More Complex, More Complex @comment node-name, next, previous, up @section The Definition of @code{copy-to-buffer} @findex copy-to-buffer After understanding how @code{append-to-buffer} works, it is easy to understand @code{copy-to-buffer}. This function copies text into a buffer, but instead of adding to the second buffer, it replaces the previous text in the second buffer. The code for the @code{copy-to-buffer} function is almost the same as the code for @code{append-to-buffer}, except that @code{erase-buffer} and a second @code{save-excursion} are used. (@xref{append-to-buffer, , The Definition of @code{append-to-buffer}}, for the description of @code{append-to-buffer}.) The body of @code{copy-to-buffer} looks like this @example @group @dots{} (interactive "BCopy to buffer:@: \nr") (let ((oldbuf (current-buffer))) (save-excursion (set-buffer (get-buffer-create buffer)) (erase-buffer) (save-excursion (insert-buffer-substring oldbuf start end))))) @end group @end example This code is similar to the code in @code{append-to-buffer}: it is only after changing to the buffer to which the text will be copied that the definition for this function diverges from the definition for @code{append-to-buffer}: the @code{copy-to-buffer} function erases the buffer's former contents. (This is what is meant by `replacement'; to replace text, Emacs erases the previous text and then inserts new text.) After erasing the previous contents of the buffer, @code{save-excursion} is used for a second time and the new text is inserted. Why is @code{save-excursion} used twice? Consider again what the function does. @need 1250 In outline, the body of @code{copy-to-buffer} looks like this: @example @group (let (@var{bind-}@code{oldbuf}@var{-to-value-of-}@code{current-buffer}) (save-excursion ; @r{First use of @code{save-excursion}.} @var{change-buffer} (erase-buffer) (save-excursion ; @r{Second use of @code{save-excursion}.} @var{insert-substring-from-}@code{oldbuf}@var{-into-buffer}))) @end group @end example The first use of @code{save-excursion} returns Emacs to the buffer from which the text is being copied. That is clear, and is just like its use in @code{append-to-buffer}. Why the second use? The reason is that @code{insert-buffer-substring} always leaves point at the @emph{end} of the region being inserted. The second @code{save-excursion} causes Emacs to leave point at the beginning of the text being inserted. In most circumstances, users prefer to find point at the beginning of inserted text. (Of course, the @code{copy-to-buffer} function returns the user to the original buffer when done---but if the user @emph{then} switches to the copied-to buffer, point will go to the beginning of the text. Thus, this use of a second @code{save-excursion} is a little nicety.) @node insert-buffer, beginning-of-buffer, copy-to-buffer, More Complex @comment node-name, next, previous, up @section The Definition of @code{insert-buffer} @findex insert-buffer @code{insert-buffer} is yet another buffer-related function. This command copies another buffer @emph{into} the current buffer. It is the reverse of @code{append-to-buffer} or @code{copy-to-buffer}, since they copy a region of text @emph{from} the current buffer to another buffer. In addition, this code illustrates the use of @code{interactive} with a buffer that might be @dfn{read-only} and the important distinction between the name of an object and the object actually referred to. Here is the code: @example @group (defun insert-buffer (buffer) "Insert after point the contents of BUFFER. Puts mark after the inserted text. BUFFER may be a buffer or a buffer name." (interactive "*bInsert buffer:@: ") @end group @group (or (bufferp buffer) (setq buffer (get-buffer buffer))) (let (start end newmark) (save-excursion (save-excursion (set-buffer buffer) (setq start (point-min) end (point-max))) @end group @group (insert-buffer-substring buffer start end) (setq newmark (point))) (push-mark newmark))) @end group @end example As with other function definitions, you can use a template to see an outline of the function: @example @group (defun insert-buffer (buffer) "@var{documentation}@dots{}" (interactive "*bInsert buffer:@: ") @var{body}@dots{}) @end group @end example @menu * insert interactive expression:: A read-only situation. * insert-buffer body:: The body has an @code{or} and a @code{ let}. * if & or:: Using an @code{if} instead of an @code{or}. * insert or:: How the @code{or} expression works. * insert let:: Two @code{save-excursion} expressions. @end menu @node insert interactive expression, insert-buffer body, insert-buffer, insert-buffer @comment node-name, next, previous, up @subsection The Interactive Expression in @code{insert-buffer} @findex interactive, @r{example use of} In @code{insert-buffer}, the argument to the @code{interactive} declaration has two parts, an asterisk, @samp{*}, and @samp{bInsert buffer:@: }. @menu * read-only buffer:: * @samp{b} for interactive:: @end menu @node read-only buffer, @samp{b} for interactive, insert interactive expression, insert interactive expression @comment node-name, next, previous, up @unnumberedsubsubsec A Read-only Buffer @cindex Read-only buffer @cindex Asterisk for read-only buffer @findex * @r{for read-only buffer} The asterisk is for the situation when the buffer is a read-only buffer---a buffer that cannot be modified. If @code{insert-buffer} is called on a buffer that is read-only, a message to this effect is printed in the echo area and the terminal may beep or blink at you; you will not be permitted to insert anything into current buffer. The asterisk does not need to be followed by a newline to separate it from the next argument. @node @samp{b} for interactive, , read-only buffer, insert interactive expression @comment node-name, next, previous, up @unnumberedsubsubsec @samp{b} in an Interactive Expression The next argument in the interactive expression starts with a lower case @samp{b}. (This is different from the code for @code{append-to-buffer}, which uses an upper-case @samp{B}. @xref{append-to-buffer, , The Definition of @code{append-to-buffer}}.) The lower-case @samp{b} tells the Lisp interpreter that the argument for @code{insert-buffer} should be an existing buffer or else its name. (The upper-case @samp{B} option provides for the possibility that the buffer does not exist.) Emacs will prompt you for the name of the buffer, offering you a default buffer, with name completion enabled. If the buffer does not exist, you receive a message that says ``No match''; your terminal may beep at you as well. @node insert-buffer body, if & or, insert interactive expression, insert-buffer @comment node-name, next, previous, up @subsection The Body of the @code{insert-buffer} Function The body of the @code{insert-buffer} function has two major parts: an @code{or} expression and a @code{let} expression. The purpose of the @code{or} expression is to ensure that the argument @code{buffer} is bound to a buffer and not just the name of a buffer. The body of the @code{let} expression contains the code which copies the other buffer into the current buffer. @need 1250 In outline, the two expressions fit into the @code{insert-buffer} function like this: @example @group (defun insert-buffer (buffer) "@var{documentation}@dots{}" (interactive "*bInsert buffer:@: ") (or @dots{} @dots{} @end group @group (let (@var{varlist}) @var{body-of-}@code{let}@dots{} ) @end group @end example To understand how the @code{or} expression ensures that the argument @code{buffer} is bound to a buffer and not to the name of a buffer, it is first necessary to understand the @code{or} function. Before doing this, let me rewrite this part of the function using @code{if} so that you can see what is done in a manner that will be familiar. @node if & or, insert or, insert-buffer body, insert-buffer @comment node-name, next, previous, up @subsection @code{insert-buffer} With an @code{if} Instead of an @code{or} The job to be done is to make sure the value of @code{buffer} is a buffer itself and not the name of a buffer. If the value is the name, then the buffer itself must be got. You can imagine yourself at a conference where an usher is wandering around holding a list with your name on it and looking for you: the usher is ``bound'' to your name, not to you; but when the usher finds you and takes your arm, the usher becomes ``bound'' to you. In Lisp, you might describe this situation like this: @example @group (if (not (holding-on-to-guest)) (find-and-take-arm-of-guest)) @end group @end example We want to do the same thing with a buffer---if we do not have the buffer itself, we want to get it. Using a predicate called @code{bufferp} that tells us whether we have a buffer (rather than its name), we can write the code like this: @example @group (if (not (bufferp buffer)) ; @r{if-part} (setq buffer (get-buffer buffer))) ; @r{then-part} @end group @end example @noindent Here, the true-or-false-test of the @code{if} expression is @w{@code{(not (bufferp buffer))}}; and the then-part is the expression @w{@code{(setq buffer (get-buffer buffer))}}. In the test, the function @code{bufferp} returns true if its argument is a buffer---but false if its argument is the name of the buffer. (The last character of the function name @code{bufferp} is the character @samp{p}; as we saw earlier, such use of @samp{p} is a convention that indicates that the function is a predicate, which is a term that means that the function will determine whether some property is true or false. @xref{Wrong Type of Argument, , Using the Wrong Type Object as an Argument}.) The function @code{not} precedes the expression @code{(bufferp buffer)}, so the true-or-false-test looks like this: @example (not (bufferp buffer)) @end example @noindent @code{not} is a function the returns true if its argument is false and false if its argument is true. So if @code{(bufferp buffer)} returns true, the @code{not} expression returns false and vice-versa: what is ``not true'' is false and what is ``not false'' is true. Using this test, the @code{if} expression works as follows: when the value of the variable @code{buffer} is actually a buffer rather then its name, the true-or-false-test returns false and the @code{if} expression does not evaluate the then-part. This is fine, since we do not need to do anything to the variable @code{buffer} if it really is a buffer. On the other hand, when the value of @code{buffer} is not a buffer itself, but the name of a buffer, the true-or-false-test returns true and the then-part of the expression is evaluated. In this case, the then-part is @code{(setq buffer (get-buffer buffer))}. This expression uses the @code{get-buffer} function to return an actual buffer itself, given its name. The @code{setq} then sets the variable @code{buffer} to the value of the buffer itself, replacing its previous value (which was the name of the buffer). @node insert or, insert let, if & or, insert-buffer @comment node-name, next, previous, up @subsection The @code{or} in the Body The purpose of the @code{or} expression in the @code{insert-buffer} function is to ensure that the argument @code{buffer} is bound to a buffer and not just the name of a buffer. The previous section shows how the job could have been done using an @code{if} expression. However, the @code{insert-buffer} function actually uses @code{or}. To understand this, it is necessary to understand how @code{or} works. @findex or An @code{or} function can have any number of arguments. It evaluates each argument in turn and returns the value of the first of its arguments that is not @code{nil}. Also, and this is a crucial feature of @code{or}, it does not evaluate any subsequent arguments after returning the first non-@code{nil} value. The @code{or} expression looks like this: @example @group (or (bufferp buffer) (setq buffer (get-buffer buffer))) @end group @end example @noindent The first argument to @code{or} is the expression @code{(bufferp buffer)}. This expression returns true (a non-@code{nil} value) if the buffer is actually a buffer, and not just the name of a buffer. In the @code{or} expression, if this is the case, the @code{or} expression returns this true value and does not evaluate the next expression---and this is fine with us, since we do not want to do anything to the value of @code{buffer} if it really is a buffer. On the other hand, if the value of @code{(bufferp buffer)} is @code{nil}, which it will be if the value of @code{buffer} is the name of a buffer, the Lisp interpreter evaluates the next element of the @code{or} expression. This is the expression @code{(setq buffer (get-buffer buffer))}. This expression returns a non-@code{nil} value, which is the value to which it sets the variable @code{buffer}---and this value is a buffer itself, not the name of a buffer. The result of all this is that the symbol @code{buffer} is always bound to a buffer itself rather than the name of a buffer. All this is necessary because the @code{set-buffer} function in a following line only works with a buffer itself, not with the name to a buffer. @need 1250 Incidentally, using @code{or}, the situation with the usher would be written like this: @example (or (holding-on-to-guest) (find-and-take-arm-of-guest)) @end example @node insert let, , insert or, insert-buffer @comment node-name, next, previous, up @subsection The @code{let} Expression in @code{insert-buffer} After ensuring that the variable @code{buffer} refers to a buffer itself and not just to the name of a buffer, the @code{insert-buffer function} continues with a @code{let} expression. This specifies three local variables, @code{start}, @code{end}, and @code{newmark} and binds them to the initial value @code{nil}. These variables are used inside the remainder of the @code{let} and temporarily hide any other occurrence of variables of the same name in Emacs until the end of the @code{let}. The body of the @code{let} contains two @code{save-excursion} expressions. First, we will look at the inner @code{save-excursion} expression in detail. The expression looks like this: @example @group (save-excursion (set-buffer buffer) (setq start (point-min) end (point-max))) @end group @end example @noindent The expression @code{(set-buffer buffer)} changes Emacs's attention from the current buffer to the one from which the text will copied. In that buffer, the variables @code{start} and @code{end} are set to the beginning and end of the buffer, using the commands @code{point-min} and @code{point-max}. Note that we have here an illustration of how @code{setq} is able to set two variables in the same expression. @code{setq}'s first argument is set to the value of its second and its third argument is set to the value of its fourth. After the body of the inner @code{save-excursion} is evaluated, the @code{save-excursion} restores the original buffer, but @code{start} and @code{end} remain set to the values of the beginning and end of the buffer from which the text will be copied. @need 1250 The outer @code{save-excursion} expression looks like this: @example @group (save-excursion (@var{inner-}@code{save-excursion}@var{-expression} (@var{go-to-new-buffer-and-set-}@code{start}@var{-and-}@code{end}) (insert-buffer-substring buffer start end) (setq newmark (point))) @end group @end example @noindent The @code{insert-buffer-substring} function copies the text @emph{into} the current buffer @emph{from} the region indicated by @code{start} and @code{end} in @code{buffer}. Since the whole of the second buffer lies between @code{start} and @code{end}, the whole of the second buffer is copied into the buffer you are editing. Next, the value of point, which will be at the end of the inserted text, is recorded in the variable @code{newmark}. After the body of the outer @code{save-excursion} is evaluated, point and mark are relocated to their original places. However, it is convenient to locate a mark at the end of the newly inserted text and locate point at its beginning. The @code{newmark} variable records the end of the inserted text. In the last line of the @code{let} expression, the @code{(push-mark newmark)} expression function sets a mark to this location. (The previous location of the mark is still accessible; it is recorded on the mark ring and you can go back to it with @kbd{C-u C-@key{SPC}}.) Meanwhile, point is located at the beginning of the inserted text, which is where it was before you called the insert function. @need 1250 The whole @code{let} expression looks like this: @example @group (let (start end newmark) (save-excursion (save-excursion (set-buffer buffer) (setq start (point-min) end (point-max))) (insert-buffer-substring buffer start end) (setq newmark (point))) (push-mark newmark)) @end group @end example Like the @code{append-to-buffer} function, the @code{insert-buffer} function uses @code{let}, @code{save-excursion}, and @code{set-buffer}. In addition, the function illustrates one way to use @code{or}. All these functions are building blocks that we will find and use again and again. @node beginning-of-buffer, Second Buffer Related Review, insert-buffer, More Complex @comment node-name, next, previous, up @section Complete Definition of @code{beginning-of-buffer} @findex beginning-of-buffer The basic structure of the @code{beginning-of-buffer} function has already been discussed. (@xref{simplified-beginning-of-buffer, , A Simplified @code{beginning-of-buffer} Definition}.) This section describes the complex part of the definition. As previously described, when invoked without an argument, @code{beginning-of-buffer} moves the cursor to the beginning of the buffer, leaving the mark at the previous position. However, when the command is invoked with a number between one and ten, the function considers that number to be a fraction of the length of the buffer, measured in tenths, and Emacs moves the cursor that fraction of the way from the beginning of the buffer. Thus, you can either call this function with the key command @kbd{M-<}, which will move the cursor to the beginning of the buffer, or with a key command such as @kbd{C-u 7 M-<} which will move the cursor to a point 70% of the way through the buffer. If a number bigger than ten is used for the argument, it moves to the end of the buffer. The @code{beginning-of-buffer} function can be called with or without an argument. The use of the argument is optional. @menu * Optional Arguments:: * beginning-of-buffer opt arg:: Example with optional argument. * beginning-of-buffer complete:: @end menu @node Optional Arguments, beginning-of-buffer opt arg, beginning-of-buffer, beginning-of-buffer @subsection Optional Arguments Unless told otherwise, Lisp expects that a function with an argument in its function definition will be called with a value for that argument. If that does not happen, you get an error and a message that says @samp{Wrong number of arguments}. @cindex Optional arguments @cindex Keyword @findex optional However, optional arguments are a feature of Lisp: a @dfn{keyword} may be used to tell the Lisp interpreter that an argument is optional. The keyword is @code{&optional}. (The @samp{&} in front of @samp{optional} is part of the keyword.) In a function definition, if an argument follows the keyword @code{&optional}, a value does not need to be passed to that argument when the function is called. The first line of the function definition of @code{beginning-of-buffer} therefore looks like this: @example (defun beginning-of-buffer (&optional arg) @end example @need 1250 In outline, the whole function looks like this: @example @group (defun beginning-of-buffer (&optional arg) "@var{documentation}@dots{}" (interactive "P") (push-mark) (goto-char (@var{if-there-is-an-argument} @var{figure-out-where-to-go} @var{else-go-to} (point-min)))) @end group @end example The function is similar to @code{simplified-beginning-of-buffer} except that the @code{interactive} expression has @code{"P"} as an argument and the @code{goto-char} function is followed by an if-then-else expression that figures out where to put the cursor if there is an argument. The @code{"P"} in the @code{interactive} expression tells Emacs to pass a prefix argument, if there is one, to the function. A prefix argument is made by typing the @key{META} key followed by a number, or by typing @kbd{C-u} and then a number (if you don't type a number, @kbd{C-u} defaults to 4). The true-or-false-test of the @code{if} expression is simple: it is simply the argument @code{arg}. If @code{arg} has a value that is not @code{nil}, which will be the case if @code{beginning-of-buffer} is called with an argument, then this true-or-false-test will return true and the then-part of the @code{if} expression will be evaluated. On the other hand, if @code{beginning-of-buffer} is not called with an argument, the value of @code{arg} will be @code{nil} and the else-part of the @code{if} expression will be evaluated. The else-part is simply @code{point-min}, and when this is the outcome, the whole @code{goto-char} expression is @code{(goto-char (point-min))}, which is how we saw the @code{beginning-of-buffer} function in its simplified form. @node beginning-of-buffer opt arg, beginning-of-buffer complete, Optional Arguments, beginning-of-buffer @subsection @code{beginning-of-buffer} with an Argument When @code{beginning-of-buffer} is called with an argument, an expression is evaluated which calculates what value to pass to @code{goto-char}. This expression is rather complicated at first sight. It includes an inner @code{if} expression and much arithmetic. It looks like this: @example @group (if (> (buffer-size) 10000) ;; @r{Avoid overflow for large buffer sizes!} (* (prefix-numeric-value arg) (/ (buffer-size) 10)) (/ (+ 10 (* (buffer-size) (prefix-numeric-value arg))) 10)) @end group @end example Like other complex-looking expressions, this one can be distangled by looking at it as parts of a template, in this case, the template for an if-then-else expression. When in skeletal form, the expression looks like this: @example @group (if (@var{buffer-is-large} @var{divide-buffer-size-by-10-and-multiply-by-arg} @var{else-use-alternate-calculation} @end group @end example The true-or-false-test of this inner @code{if} expression checks the size of the buffer. The reason for this is that version 18 Emacs Lisp uses numbers that are no bigger than eight million or so (bigger numbers are not needed) and in the computation that follows, Emacs might try to use over-large numbers if the buffer were large. The term `overflow', mentioned in the comment, means numbers that are over large. There are two cases: if the buffer is large and if it is not. @menu * large-case:: Division and multiplication in a large buffer. * small-case:: Functions embedded in parentheses. @end menu @node large-case, small-case, beginning-of-buffer opt arg, beginning-of-buffer opt arg @comment node-name, next, previous, up @unnumberedsubsubsec What happens in a large buffer In @code{beginning-of-buffer}, the inner @code{if} expression tests whether the size of the buffer is greater than 10,000 characters. To do this, it uses the @code{>} function and the @code{buffer-size} function. The line looks like this: @example (if (> (buffer-size) 10000) @end example @noindent When the buffer is large, the then-part of the @code{if} expression is evaluated. It reads like this (after formatting for easy reading): @example @group (* (prefix-numeric-value arg) (/ (buffer-size) 10)) @end group @end example @noindent This expression is a multiplication, with two arguments to the function @code{*}. The first argument is @code{(prefix-numeric-value arg)}. When @code{"P"} is used as the argument for @code{interactive}, the value passed to the function as its argument is passed a ``raw prefix argument'', and not a number. (It is a number in a list.) To perform the arithmetic, a conversion is necessary, and @code{prefix-numeric-value} does the job. @findex / @r{(division)} @cindex Division The second argument is @code{(/ (buffer-size) 10)}. This expression divides the numeric value of the buffer by ten. This produces a number that tells how many characters make up one tenth of the buffer size. (In Lisp, @code{/} is used for division, just as @code{*} is used for multiplication.) In the multiplication expression as a whole, this amount is multiplied by the value of the prefix argument---the multiplication looks like this: @example @group (* @var{numeric-value-of-prefix-arg} @var{number-of-characters-in-one-tenth-of-the-buffer}) @end group @end example @noindent If, for example, the prefix argument is @samp{7}, the one-tenth value will be multiplied by 7 to give a position 70% of the way through the buffer. The result of all this is that if the buffer is large, the @code{goto-char} expression reads like this: @example @group (goto-char (* (prefix-numeric-value arg) (/ (buffer-size) 10))) @end group @end example This puts the cursor where we want it. @node small-case, , large-case, beginning-of-buffer opt arg @comment node-name, next, previous, up @unnumberedsubsubsec What happens in a small buffer If the buffer contains fewer than 10,000 characters, a slightly different computation is performed. You might think this is not necessary, since the first computation could do the job. However, in a small buffer, the first method may not put the cursor on exactly the desired line; the second method does a better job. The code looks like this: @c Keep this on one line. Put into smallexample if necessary. @example (/ (+ 10 (* (buffer-size) (prefix-numeric-value arg))) 10)) @end example @noindent This is code in which you figure out what happens by discovering how the functions are embedded in parentheses. It is easier to read if you reformat it with each expression indented more deeply than its enclosing expression: @example @group (/ (+ 10 (* (buffer-size) (prefix-numeric-value arg))) 10)) @end group @end example @noindent Looking at parentheses, we see that the innermost operation is @code{(prefix-numeric-value arg)}, which converts the raw argument to a number. This number is multiplied by the buffer size in the following expression: @example (* (buffer-size) (prefix-numeric-value arg) @end example @noindent This multiplication creates a number that may be larger than the size of the buffer---seven times larger if the argument is 7, for example. Ten is then added to this number and finally the large number is divided by ten to provide a value that is one character larger than the percentage position in the buffer. The number that results from all this is passed to @code{goto-char} and the cursor is moved to that point. @node beginning-of-buffer complete, , beginning-of-buffer opt arg, beginning-of-buffer @comment node-name, next, previous, up @subsection The Complete @code{beginning-of-buffer} Here is the complete text of the @code{beginning-of-buffer} function: @example @group (defun beginning-of-buffer (&optional arg) "Move point to the beginning of the buffer; leave mark at previous position. With arg N, put point N/10 of the way from the true beginning. Don't use this in Lisp programs! \(goto-char (point-min)) is faster and does not set the mark." (interactive "P") (push-mark) @end group @group (goto-char (if arg (if (> (buffer-size) 10000) ;; @r{Avoid overflow for large buffer sizes!} (* (prefix-numeric-value arg) (/ (buffer-size) 10)) @end group @group (/ (+ 10 (* (buffer-size) (prefix-numeric-value arg))) 10)) (point-min))) (if arg (forward-line 1))) @end group @end example @noindent Except for two small points, the previous discussion shows how this function works. The first point deals with a detail in the documentation string, and the second point concerns the last line of the function. In the documentation string, there is reference to an expression: @example \(goto-char (point-min)) @end example @noindent A @samp{\} is used before the first parenthesis of this expression. This @samp{\} tells the Lisp interpreter that the expression should be printed as shown in the documentation rather than evaluated as an symbolic expression, which is what it looks like. Finally, the last line of the @code{beginning-of-buffer} command says to move point to the beginning of the next line if the command is invoked with an argument: @example (if arg (forward-line 1))) @end example @noindent This puts the cursor at the beginning of the first line after the appropriate tenths position in the buffer. This is a flourish that means that the cursor is always located @emph{at least} the requested tenths of the way through the buffer, which is a nicety that is, perhaps, not necessary, but which, if it did not occur, would be sure to draw complaints. @node Second Buffer Related Review, &optional Exercise , beginning-of-buffer, More Complex @comment node-name, next, previous, up @section Review Here is a brief summary of some of the topics covered in this chapter. @table @code @item or Evaluate each argument in sequence, and return the value of the first argument that is not @code{nil}; if none return a value that is not @code{nil}, return @code{nil}. In brief, return the first true value of the arguments; return a true value if one @emph{or} any of the other are true. @item and Evaluate each argument in sequence, and if any are @code{nil}, return @code{nil}; if none are @code{nil}, return the value of the last argument. In brief, return a true value only if all the arguments are true; return a true value if one @emph{and} each of the others is true. @item &optional A keyword used to indicate that an argument to a function definition is optional; this means that the function can be evaluated without the argument, if desired. @item prefix-numeric-value Convert the `raw prefix argument' produced by @code{(interactive "P")} to a numeric value. @item forward-line Move point forward to the beginning of the next line, or if the argument is greater than one, forward that many lines. If it can't move as far forward as it is supposed to, @code{forward-line} goes forward as far as it can and then returns a count of the number of additional lines it was supposed to move but couldn't. @item erase-buffer Delete the entire contents of the current buffer. @item bufferp Return @code{t} if its argument is a buffer; otherwise return @code{nil}. @end table @node &optional Exercise , , Second Buffer Related Review, More Complex @section @code{&optional} Argument Exercise Write an interactive function with an optional argument that tests whether its argument, a number, is greater or less than the value of @code{fill-column}, and tells you which, in a message. However, if you do not pass an argument to the function, use 56 as a default value. @node Narrowing & Widening, car cdr & cons, More Complex, Top @comment node-name, next, previous, up @chapter Narrowing and Widening @cindex Focusing attention (narrowing) @cindex Narrowing @cindex Widening Narrowing is a feature of Emacs that makes it possible for you to focus on a specific part of a buffer, and work without accidentally changing other parts. Narrowing is normally disabled since it can confuse novices. @menu * narrowing advantages:: The Advantages of Narrowing * save-restriction:: The @code{save-restriction} special form. * what-line:: The number of the line that point is on. * narrow Exercise:: @end menu @node narrowing advantages, save-restriction, Narrowing & Widening, Narrowing & Widening @ifinfo @heading The Advantages of Narrowing @end ifinfo With narrowing, the rest of a buffer is made invisible, as if it weren't there. This is an advantage if, for example, you want to replace a word in one part of a buffer but not in another: you narrow to the part you want and the replacement is carried out only in that section, not in the rest of the buffer. Searches will only work within a narrowed region, not outside of one, so if you are fixing a part of a document, you can keep yourself from accidentally finding parts you do not need to fix by narrowing just to the region you want. However, narrowing does make the rest of the buffer invisible, which can scare people who inadvertently invoke narrowing and think they have deleted a part of their file. Moreover, the @code{undo} command (which is usually bound to @kbd{C-x u}) does not turn off narrowing (nor should it), so people can become quite desperate if they do not know that they can return the rest of a buffer to visibility with the @code{widen} command. (In Emacs version 18, the key binding for @code{widen} is @kbd{C-x w}; in version 19, it is @kbd{C-x n w}.) Narrowing is just as useful to the Lisp interpreter as to a human. Often, an Emacs Lisp function is designed to work on just part of a buffer; or conversely, an Emacs Lisp function needs to work on all of a buffer that has been narrowed. The @code{what-line} function, for example, removes the narrowing from a buffer, if it has any narrowing and when it has finished its job, restores the narrowing to what it was. On the other hand, the @code{count-lines} function, which is called by @code{what-line}, uses narrowing to restrict itself to just that portion of the buffer in which it is interested and then restores the previous situation. @node save-restriction, what-line, narrowing advantages, Narrowing & Widening @comment node-name, next, previous, up @section The @code{save-restriction} Special Form @findex save-restriction In Emacs Lisp, you can use the @code{save-restriction} special form to keep track of whatever narrowing is in effect, if any. When the Lisp interpreter meets with @code{save-restriction}, it executes the code in the body of the @code{save-restriction} expression, and then undoes any changes to narrowing that the code caused. If, for example, the buffer is narrowed and the code that follows @code{save-restriction} gets rid of the narrowing, @code{save-restriction} returns the buffer to its narrowed region afterwards. In the @code{what-line} command, any narrowing the buffer may have is undone by the @code{widen} command that immediately follows the @code{save-restriction} command. Any original narrowing is restored just before the completion of the function. @need 1250 The template for a @code{save-restriction} expression is simple: @example @group (save-restriction @var{body}@dots{} ) @end group @end example @noindent The body of the @code{save-restriction} is one or more expressions that will be evaluated in sequence by the Lisp interpreter. Finally, a point to note: when you use both @code{save-excursion} and @code{save-restriction}, one right after the other, you should use @code{save-excursion} outermost. If you write them in reverse order, you may fail to record narrowing in the buffer to which Emacs switches after calling @code{save-excursion}. Thus, when written together, @code{save-excursion} and @code{save-restriction} should be written like this: @example @group (save-excursion (save-restriction @var{body}@dots{})) @end group @end example @node what-line, narrow Exercise, save-restriction, Narrowing & Widening @comment node-name, next, previous, up @section @code{what-line} @findex what-line @cindex Widening, example of The @code{what-line} command tells you the number of the line in which the cursor is located. The function illustrates the use of the @code{save-restriction} and @code{save-excursion} commands. Here is the text of the function in full: @example @group (defun what-line () "Print the current line number (in the buffer) of point." (interactive) (save-restriction (widen) (save-excursion (beginning-of-line) (message "Line %d" (1+ (count-lines 1 (point))))))) @end group @end example The function has a documentation line and is interactive, as you would expect. The next two lines use the functions @code{save-restriction} and @code{widen}. The @code{save-restriction} special form notes whatever narrowing is in effect, if any, in the current buffer and restores that narrowing after the code in the body of the @code{save-restriction} has been evaluated. The @code{save-restriction} special form is followed by @code{widen}. This function undoes any narrowing the current buffer may have had when @code{what-line} was called. (The narrowing that was there is the narrowing that @code{save-restriction} remembers.) This widening makes it possible for the line counting commands to count from the beginning of the buffer. Otherwise, they would have been limited to counting within the accessible region. Any original narrowing is restored just before the completion of the function by the @code{save-restriction} special form. The call to @code{widen} is followed by @code{save-excursion}, which saves the location of the cursor (i.e., of point) and of the mark, and restores them after the code in the body of the @code{save-excursion} uses the @code{beginning-of-line} function to move point. (Note that the @code{(widen)} expression comes between @code{save-restriction} and @code{save-excursion}. When you write the two @code{save- @dots{}} expressions in sequence, write @code{save-excursion} outermost.) The last two lines of the @code{what-line} function are functions to count the number of lines in the buffer and then print the number in the echo area. @example @group (message "Line %d" (1+ (count-lines 1 (point))))))) @end group @end example The @code{message} function prints a one-line message at the bottom of the Emacs screen. The first argument is inside of quotation marks and is printed as a string of characters. However, it may contain @samp{%d}, @samp{%s}, or @samp{%c} to print arguments that follow the string. @samp{%d} prints the argument as a decimal, so the message will say something such as @samp{Line 243}. The number that is printed in place of the @samp{%d} is computed by the last line of the function: @example (1+ (count-lines 1 (point))) @end example @noindent What this does is count the lines from the first position of the buffer, indicated by the @code{1}, up to @code{(point)}, and then add one to that number. (The @code{1+} function adds one to its argument.) We add one to it because line 2 has only one line before it, and @code{count-lines} counts only the lines @emph{before} the current line. After @code{count-lines} has done it job, and the message has been printed in the echo area, the @code{save-excursion} restores point and mark to their original positions; and @code{save-restriction} restores the original narrowing, if any. @node narrow Exercise, , what-line, Narrowing & Widening @section Exercise with Narrowing Write a function that will display the first 60 characters of the current buffer, even if you have narrowed the buffer to its latter half so that the first line is inaccessible. Restore point, mark, and narrowing. For this exercise, you need to use @code{save-restriction}, @code{widen}, @code{goto-char}, @code{point-min}, @code{buffer-substring}, @code{message}, and other functions, a whole potpourri. @node car cdr & cons, Cutting & Storing Text, Narrowing & Widening, Top @comment node-name, next, previous, up @chapter @code{car}, @code{cdr}, @code{cons}: Fundamental Functions @findex car, @r{introduced} @findex cdr, @r{introduced} In Lisp, @code{car}, @code{cdr}, and @code{cons} are fundamental functions. The @code{cons} function is used to construct lists, and the @code{car} and @code{cdr} functions are used to take them apart. In the walk through of the @code{copy-region-as-kill} function, we will see @code{cons} as well as two variants on @code{cdr}, namely, @code{setcdr} and @code{nthcdr}. (@xref{copy-region-as-kill}.) @menu * Strange Names:: An historical aside: why the strange names? * car & cdr:: Functions for extracting part of a list. * cons:: Constructing a list. * nthcdr:: Calling @code{cdr} repeatedly. * setcar:: Changing the first element of a list. * setcdr:: Changing the rest of a list. * cons Exercise:: @end menu @node Strange Names, car & cdr, car cdr & cons, car cdr & cons @ifinfo @heading Strange Names @end ifinfo The name of the @code{cons} function is not unreasonable: it is an abbreviation of the word `construct'. The origins of the names for @code{car} and @code{cdr}, on the other hand, are esoteric: @code{car} is an acronym from the phrase `Contents of the Address part of the Register'; and @code{cdr} (pronounced `could-er') is an acronym from the phrase `Contents of the Decrement part of the Register'. These phrases refer to specific pieces of hardware on the very early computer on which the original Lisp was developed. Besides being obsolete, the phrases have been completely irrelevant for more than 25 years to anyone thinking about Lisp. Nonetheless, although a few brave scholars have begun to use more reasonable names for these functions, the old terms are still in use. In particular, since the terms are used in the Emacs Lisp source code, we will use them in this introduction. @node car & cdr, cons, Strange Names, car cdr & cons @comment node-name, next, previous, up @section @code{car} and @code{cdr} The @code{car} of a list is, quite simply, the first item in the list. Thus the @code{car} of the list @code{(rose violet daisy buttercup)} is @code{rose}. If you are reading this in Info in GNU Emacs, you can see this by evaluating the following: @example (car '(rose violet daisy buttercup)) @end example @noindent After evaluating the expression, @code{rose} will appear in the echo area. Clearly, a more reasonable name for the @code{car} function would be @code{first} and this is often suggested. @code{car} does not remove the first item from the list; it only reports what it is. After @code{car} has been applied to a list, the list is still the same as it was. In the jargon, @code{car} is `non-destructive'. This feature turns out to be important. The @code{cdr} of a list is the rest of the list, that is, the @code{cdr} function returns the part of the list that follows the first item. Thus, while the @code{car} of the list @code{'(rose violet daisy buttercup)} is @code{rose}, the rest of the list, the value returned by @code{cdr}, is @code{(violet daisy buttercup)}. @need 1250 You can see this by evaluating the following in the usual way: @example (cdr '(rose violet daisy buttercup)) @end example @noindent When you evaluate this, @code{(violet daisy buttercup)} will appear in the echo area. Like @code{car}, @code{cdr} does not remove any elements form the list---it just returns a report of what the second and subsequent elements are. Incidentally, in the example, the list of flowers is quoted. If it were not, the Lisp interpreter would try to evaluate the list by calling @code{rose} as a function. In this example, we do not want to do that. Clearly, a more reasonable name for @code{cdr} would be @code{rest}. (There is a lesson here: when you name new functions, consider very carefully about what you are doing, since you may be stuck with the names for far longer than you expect. The reason this document perpetuates these names is that the Emacs Lisp source code uses them, and if I did not use them, you would have a hard time reading the code; but do please try to avoid using these terms yourself. The people who come after you will be grateful to you.) When @code{car} and @code{cdr} are applied to a list made up of symbols, such as the list @code{(pine fir oak maple)}, the element of the list returned by the function @code{car} is the symbol @code{pine} without any parentheses around it. @code{pine} is the first element in the list. However, the @code{cdr} of the list is a list itself, @code{(fir oak maple)}, as you can see by evaluating the following expressions in the usual way: @example @group (car '(pine fir oak maple)) (cdr '(pine fir oak maple)) @end group @end example On the other hand, in a list of lists, the first element is itself a list. @code{car} returns this first element as a list. For example, the following list contains three sub-lists, a list of carnivores, a list of herbivores and a list of sea mammals: @example @group (car '((lion tiger cheetah) (gazelle antelope zebra) (whale dolphin seal))) @end group @end example @noindent In this case, the first element or @code{car} of the list is the list of carnivores, @code{(lion tiger cheetah)}, and the rest of the list is @code{((gazelle antelope zebra) (whale dolphin seal))}. @example @group (cdr '((lion tiger cheetah) (gazelle antelope zebra) (whale dolphin seal))) @end group @end example It is worth saying again that @code{car} and @code{cdr} are non-destructive---that is, they do not modify or change lists to which they are applied. This is very important for how they are used. Also, in the first chapter, in the discussion about atoms, I said that in Lisp, ``certain kinds of atom, such as an array, can be separated into parts; but the mechanism for doing this is different from the mechanism for splitting a list. As far as Lisp is concerned, the atoms of a list are unsplittable.'' (@xref{Lisp Atoms}.) The @code{car} and @code{cdr} functions are used for splitting lists and are considered fundamental to Lisp. Since they cannot split or gain access to the parts of an array, an array is considered an atom. Conversely, the other fundamental function, @code{cons}, can put together or construct a list, but not an array. (Arrays are handled by array-specific functions. @xref{Arrays, , Arrays, elisp, The GNU Emacs Lisp Reference Manual}.) @node cons, nthcdr, car & cdr, car cdr & cons @comment node-name, next, previous, up @section @code{cons} @findex cons, @r{introduced} The @code{cons} function constructs lists; it is the inverse of @code{car} and @code{cdr}. For example, @code{cons} can be used to make a four element list from the three element list, @code{(fir oak maple)}: @example (cons 'pine '(fir oak maple)) @end example @noindent After evaluating this list, you will see @example (pine fir oak maple) @end example @noindent appear in the echo area. @code{cons} puts a new element at the beginning of a list; it attaches or pushes elements onto the list. @code{cons} must have a list to attach to.@footnote{Actually, you can @code{cons} an element to an atom to produce a dotted pair. Dotted pairs are not discussed here; see @ref{Dotted Pair Notation, , Dotted Pair Notation, elisp, The GNU Emacs Lisp Reference Manual}.} You cannot start from absolutely nothing. If you are building a list, you need to provide at least an empty list at the beginning. Here is a series of @code{cons}'s that build up a list of flowers. If you are reading this in Info in GNU Emacs, you can evaluate each of the expressions in the usual way; the value is printed in this text after @samp{@result{}}, which you may read as `evaluates to'. @example @group (cons 'buttercup ()) @result{} (buttercup) @end group @group (cons 'daisy '(buttercup)) @result{} (daisy buttercup) @end group @group (cons 'violet '(daisy buttercup)) @result{} (violet daisy buttercup) @end group @group (cons 'rose '(violet daisy buttercup)) @result{} (rose violet daisy buttercup) @end group @end example @noindent In the first example, the empty list is shown as @code{()} and a list made up of @code{buttercup} followed by the empty list is constructed. As you can see, the empty list is not shown in the list that was constructed. All that you see is @code{(buttercup)}. The empty list is not counted as an element of a list because there is nothing in an empty list. Generally speaking, an empty list is invisible. The second example, @code{(cons 'daisy '(buttercup))} constructs a new, two element list by putting @code{daisy} in front of @code{buttercup}; and the third example constructs a three element list by putting @code{violet} in front of @code{daisy} and @code{buttercup}. @menu * length:: How to find the length of a list. @end menu @node length, , cons, cons @comment node-name, next, previous, up @subsection Find the Length of a List: @code{length} @findex length You can find out how many elements there are in a list by using the Lisp function @code{length}, as in the following examples: @example @group (length '(buttercup)) @result{} 1 @end group @group (length '(daisy buttercup)) @result{} 2 @end group @group (length (cons 'violet '(daisy buttercup))) @result{} 3 @end group @end example @noindent In the third example, the @code{cons} function is used to construct a three element list which is then passed to the @code{length} function as its argument. We can also use @code{length} to count the number of elements in an empty list: @example @group (length ()) @result{} 0 @end group @end example @noindent As you would expect, the number of elements in an empty list is zero. An interesting experiment is to find out what happens if you try to find the length of no list at all; that is, if you try to call @code{length} without giving it an argument, not even an empty list: @example (length ) @end example @noindent What you see, if you evaluate this, is the error message @example Wrong number of arguments: #, 0 @end example @noindent This means is that the function receives the wrong number of arguments, zero, when it expects some other number of arguments. In this case, one argument is expected, the argument being a list whose length the function is measuring. (Note that @emph{one} list is @emph{one} argument, even if the list has many elements inside it.) The part of the error message that says @samp{#} is the name of the function. This is written with a special notation, @samp{# arg 0) (1- (point)) (1+ (point)))) (point)) (if (> arg 0) (point-max) (point-min))) @end group @end example This looks considerably more complicated, but the code can be readily understood if it is looked at part by part. The first part is: @example (if (search-forward (char-to-string char) nil t arg) @end example @noindent This fits into an @code{if} expression that does the following job, as we shall see: @example @group (if @var{able-to-locate-zapped-for-character-and-move-point-to-it} @var{then-move-point-to-the-exact-spot-and-return-this-location} @var{else-move-to-end-of-buffer-and-return-that-location}) @end group @end example @noindent Evaluation of the @code{if} expression specifies the second argument to @code{kill-region}. Since the first argument is point, this process makes it possible for @code{kill-region} to remove the text between point and the zapped-to location. We have already described how @code{search-forward} moves point as a side effect. The value that @code{search-forward} returns is @code{t} if the search is successful and either @code{nil} or an error message depending on the value of the third argument to @code{search-forward}. In this case, @code{t} is the third argument and it causes the function to return @code{nil} when the search fails. As we will see, it is easy to write the code for handling the case when the search returns @code{nil}. In the version 18 implementation of @code{zap-to-char}, the search takes place because the @code{if} causes the search expression to be evaluated as its true-or-false-test. If the search is successful, Emacs evaluates the then-part of the @code{if} expression. On the other hand, if the search fails, Emacs evaluates the else-part of the @code{if} expression. In the @code{if} expression, when the search succeeds, a @code{progn} expression is executed---which is to say, it is run as a program. As we said earlier, @code{progn} is a function that causes each of its arguments to be evaluated in sequence and then returns the value of the last one. The preceding expressions are evaluated only for the side effects they perform. The values produced by them are discarded. In this version of @code{zap-to-char}, the @code{progn} expression is executed when the @code{search-forward} function finds the character for which it is searching. The @code{progn} expression has to do two things: put point in exactly the right position; and return the location of point so that @code{kill-region} will know how far to kill to. The reason for all the code in the @code{progn} is that when @code{search-forward} finds the string it is looking for, it leaves point immediately after the last character in the target string. (In this case the target string is just one character long.) If the search is backwards, @code{search-forward} leaves point just before the first character in the target. However, this version of the @code{zap-to-char} function is designed so that it does not remove the character being zapped to. For example, if @code{zap-to-char} is to remove all the text up to a @samp{z}, this version will not remove the @samp{z} as well. So point has to be moved just enough that the zapped-to character is not removed. @menu * progn body:: The body of the @code{progn} expression @end menu @node progn body, , v-18-zap-to-char, v-18-zap-to-char @unnumberedsubsubsec The body of the @code{progn} expression The body of the @code{progn} consists of two expressions. Spread out to delineate the different parts more clearly, and with comments added, the @code{progn} expression looks like this: @example @group (progn (goto-char ; @r{First expression in @code{progn}.} (if (> arg 0) ; @r{If @code{arg} is positive,} (1- (point)) ; @r{ move back one character;} (1+ (point)))) ; @r{ else move forward one character.} (point)) ; @r{Second expression in @code{progn}:} ; @r{ return position of point.} @end group @end example @noindent The @code{progn} expression does this: when the search is forward (@code{arg} is positive), Emacs leaves point just after the searched-for character. By moving point back one position, the character is uncovered. In this case, the expression in the @code{progn} reads as follows: @code{(goto-char (1- (point)))}. This moves point one character back. (The @code{1-} function subtracts one from its argument, just as @code{1+} adds ones to its argument.) On the other hand, if the argument to @code{zap-to-character} is negative, the search will be backwards. The @code{if} detects this and the expression reads: @code{(goto-char (1+ (point)))}. (The @code{1+} function adds one to its argument.) The second and last argument to @code{progn} is the expression @code{(point)}. This expression returns the value of the position to which point is moved by the first argument to @code{progn}. This value is then returned by the @code{if} expression of which it is a part and is passed to @code{kill-region} as @code{kill-region}'s second argument. In brief, the function works like this: the first argument to @code{kill-region} is the position of the cursor when the @code{zap-to-char} command is given---the value of point at that time. The search function then moves point if the search is successful. The @code{progn} expression moves point just enough so the zapped to character is not removed, and returns the value of point after all this is done. The @code{kill-region} function then removes the region. Finally, the else-part of the @code{if} expression takes care of the situation in which the zapped-towards character is not found. If the argument to the @code{zap-to-char} function is positive (or if none is given) and the zapped-to character is not found, all the text is removed from the current position of point to the end of the accessible region of the buffer (the end of the buffer if there is no narrowing). If the @code{arg} is negative and the zapped-to character is not found, the operation goes to the beginning of the accessible region. The code for this is a simple @code{if} clause: @example (if (> arg 0) (point-max) (point-min)) @end example This says that if @code{arg} is a positive number, return the value of @code{point-max}, otherwise, return the value of @code{point-min}. For review, here is the code involving @code{kill-region}, with comments: @example @group (kill-region (point) ; @r{beginning-of-region} (if (search-forward (char-to-string char) ; @r{target} nil ; @r{limit-of-search: none} t ; @r{Return @code{nil} if fail.} arg) ; @r{repeat-count.} @end group @group (progn ; @r{then-part} (goto-char (if (> arg 0) (1- (point)) (1+ (point)))) (point)) (if (> arg 0) ; @r{else-part} (point-max) (point-min)))) @end group @end example As you can see, the version 19 implementation does slightly less than the version 18 implementation, but is much simpler. @node kill-region, delete-region, zap-to-char, Cutting & Storing Text @comment node-name, next, previous, up @section @code{kill-region} @findex kill-region The @code{zap-to-char} function uses the @code{kill-region} function. This function is very simple; leaving out part of its documentation string, it looks like this: @example @group (defun kill-region (beg end) "Kill between point and mark. The text is deleted but saved in the kill ring." (interactive "*r") (copy-region-as-kill beg end) (delete-region beg end)) @end group @end example The main point to note is that it uses the @code{delete-region} and @code{copy-region-as-kill} functions which are described in following sections. @node delete-region, defvar, kill-region, Cutting & Storing Text @comment node-name, next, previous, up @section @code{delete-region}: A Digression into C @findex delete-region @cindex C, a digression into @cindex Digression into C The @code{zap-to-char} command uses the @code{kill-region} function, which in turn uses two other functions, @code{copy-region-as-kill} and @code{delete-region}. The @code{copy-region-as-kill} function will be described in a following section; it puts a copy of the region in the kill ring so it can be yanked back. (@xref{copy-region-as-kill, , @code{copy-region-as-kill}}.) The @code{delete-region} function removes the contents of a region and you cannot get it back. Unlike the other code discussed here, @code{delete-region} is not written in Emacs Lisp; it is written in C and is one of the primitives of the GNU Emacs system. Since it is very simple, I will digress briefly from Lisp and describe it here. Like many of the other Emacs primitives, @code{delete-region} is written as an instance of a C macro, a macro being a template for code. The first section of the macro looks like this: @smallexample @group DEFUN ("delete-region", Fdelete_region, Sdelete_region, 2, 2, "r", "Delete the text between point and mark.\n\ When called from a program, expects two arguments,\n\ character numbers specifying the stretch to be deleted.") @end group @end smallexample Without getting into the details of the macro writing process, let me point out that this macro starts with the word @code{DEFUN}. The word @code{DEFUN} was chosen since the code serves the same purpose as @code{defun} does in Lisp. The word @code{DEFUN} is followed by seven parts inside of parentheses: @itemize @bullet @item The first part is the name given to the function in Lisp, in this case, @code{delete-region}. @item The second part is the name of the function in C, @code{Fdelete_region}. By convention, it starts with @samp{F}. Since C does not use hyphens in names, an underscore is used instead. @item The third part is the name for the C constant structure that records information on this function for internal use. It is the name of the function in C but begins with an @samp{S} instead of an @samp{F}. @item The fourth and fifth parts specify the minimum and maximum number of arguments the function can have. In this case, the function demands exactly 2 arguments. @item The sixth part is just like the argument that follows the @code{interactive} declaration in a function written in Lisp: a letter followed, perhaps, by a prompt. In this case, the letter is @code{"r"} which indicates that the two arguments to the function will be the position of the beginning and end of a region in the buffer. In this code, there isn't any prompt. @item The seventh part is a documentation string, just like the one for a function written in Emacs Lisp, except that every newline must be written explicitly as @samp{\n} followed by a backslash and carriage return. @end itemize The formal parameters come next, with a statement of what kind of object they are, and then what might be called the `body' of the macro. For @code{delete-region} the `body' consists of the following three lines: @example @group validate_region (&b, &e); del_range (XINT (b), XINT (e)); return Qnil; @end group @end example The first function, @code{validate_region} checks whether the values passed as the beginning and end of the region are the proper type and are within range. The second function, @code{del_range}, actually deletes the text. If the function completes its work without error, the third line returns @code{Qnil} to indicate this. @code{del_range} is a complex function we will not look into. It updates the buffer and does other things. However, it is worth looking at the two arguments passed to @code{del_range}. These are @w{@code{XINT (b)}} and @w{@code{XINT (e)}}. As far as the C language is concerned, @code{b} and @code{e} are two thirty-two bit integers that mark the beginning and end of the region to be deleted. But like other numbers in Emacs Lisp, only twenty-four bits of the thirty-two bits are used for the number; the remaining eight bits are used for keeping track of the type of information and other purposes. (On certain machines, only six bits are so used.) In this case, the eight bits are used to indicate that these numbers are for buffer positions. When bits of a number are used this way, they are called a @dfn{tag}. The use of the eight bit tag on each thirty-two bit integer made it possible to write Emacs to run much faster than it would otherwise. On the other hand, with numbers limited to twenty-four bits, Emacs buffers are limited to approximately eight megabytes. (You can sharply increase the maximum buffer size by adding defines for @code{VALBITS} and @code{GCTYPEBITS} in the @file{emacs/src/config.h} file before compiling. See the note in the @file{emacs/etc/FAQ} file that is part of the Emacs distribution.) @samp{XINT} is C macro that extracts the 24 bit number from the thirty-two bit Lisp object; the eight bits used for other purposes are discarded. So @w{@code{del_range (XINT (b), XINT (e))}} deletes the region between the beginning position, @code{b}, and the ending position, @code{e}. From the point of view of the person writing Lisp, Emacs is all very simple; but hidden underneath is a great deal of complexity to make it all work. @node defvar, copy-region-as-kill, delete-region, Cutting & Storing Text @comment node-name, next, previous, up @section Initializing a Variable with @code{defvar} @findex defvar @cindex Initializing a variable @cindex Variable initialization Unlike the @code{delete-region} function, the @code{copy-region-as-kill} function is written in Emacs Lisp. It copies a region in a buffer and saves it in a variable called the @code{kill-ring}. This section describes how this variable is created and initialized. (Again we note that the term @code{kill-ring} is a misnomer. The text that is clipped out of the buffer can be brought back; it is not a ring of corpses, but a ring of resurrectable text.) In Emacs Lisp, a variable such as the @code{kill-ring} is created and given an initial value by using the @code{defvar} special form. The name comes from ``define variable''. The @code{defvar} special form is similar to @code{setq} in that it sets the value of a variable. It is unlike @code{setq} in two ways: first, it only sets the value of the variable if the variable does not already have a value. If the variable already has a value, @code{defvar} does not override the existing value. Second, @code{defvar} has a documentation string. You can see the current value of a variable, any variable, by using the @code{describe-variable} function, which is usually invoked by typing @kbd{C-h v}. If you type @kbd{C-h v} and then @code{kill-ring} (followed by @key{RET}) when prompted, you will see what is in your current kill ring---this may be quite a lot! Conversely, if you have been doing nothing this Emacs session except read this document, you may have nothing in it. At the end of the @file{*Help*} buffer, you will see the documentation for @code{kill-ring}: @example @group Documentation: List of killed text sequences. @end group @end example The kill ring is defined by a @code{defvar} in the following way: @example @group (defvar kill-ring nil "List of killed text sequences.") @end group @end example @noindent In this variable definition, the variable is given an initial value of @code{nil}, which makes sense, since if you have saved nothing, you want nothing back if you give a @code{yank} command. The documentation string is written just like the documentation string of a @code{defun}. As with the documentation string of the @code{defun}, the first line of the documentation should be a complete sentence, since some commands, like @code{apropos}, print only the first line of documentation. Succeeding lines should not be indented; otherwise they look odd when you use @kbd{C-h v} (@code{describe-variable}). @findex edit-options, @r{introduced} @cindex Options introduced Most variables are internal to Emacs, but some are intended as options that you can readily set with the @code{edit-options} command. (These settings last only for the duration of an editing session; to set a value permanently, write a @file{.emacs} file. @xref{Emacs Initialization, , Your @file{.emacs} File}.) A readily settable variable is distinguished from others in Emacs by an asterisk, @samp{*}, in the first column of its documentation string. For example: @example @group (defvar line-number-mode nil "*Non-nil means display line number in mode line.") @end group @end example @noindent This means that you can use the @code{edit-options} command to change the value of @code{line-number-mode}. Of course, you can also change the value of @code{line-number-mode} by evaluating it within a @code{setq} expression, like this: @example (setq line-number-mode t) @end example @noindent @xref{Using setq, , Using @code{setq}}. @node copy-region-as-kill, cons & search-fwd Review, defvar, Cutting & Storing Text @comment node-name, next, previous, up @section @code{copy-region-as-kill} @findex copy-region-as-kill @findex nthcdr The @code{copy-region-as-kill} function copies a region of text from a buffer and saves it in a variable called the @code{kill-ring}. If you call @code{copy-region-as-kill} immediately after a @code{kill-region} command, Emacs appends the newly copied text to the previously copied text. This means that if you yank back the text, you get it all, from both this and the previous operation. On the other hand, if some other command precedes the @code{copy-region-as-kill}, the function copies the text into a separate entry in the kill ring. Here is the complete text of the version 18 @code{copy-region-as-kill}, formatted for clarity with several comments added: @example @group (defun copy-region-as-kill (beg end) "Save the region as if killed, but don't kill it." (interactive "r") @end group @group (if (eq last-command 'kill-region) ;; @r{then-part: Combine newly copied text} ;; @r{ with previously copied text.} (kill-append (buffer-substring beg end) (< end beg)) @end group @group ;; @r{else-part: Add newly copied text as a new element} ;; @r{ to the kill ring and shorten the kill ring if necessary.} (setq kill-ring (cons (buffer-substring beg end) kill-ring)) (if (> (length kill-ring) kill-ring-max) (setcdr (nthcdr (1- kill-ring-max) kill-ring) nil))) @end group @group (setq this-command 'kill-region) (setq kill-ring-yank-pointer kill-ring)) @end group @end example As usual, this function can be divided into its component parts: @example @group (defun copy-region-as-kill (@var{argument-list}) "@var{documentation}@dots{}" (interactive "r") @var{body}@dots{}) @end group @end example The arguments are @code{beg} and @code{end} and the function is interactive with @code{"r"}, so the two arguments must refer to the beginning and end of the region. If you have been reading though this document from the beginning, understanding these parts of a function is almost becoming routine. The documentation is somewhat confusing unless you remember that the word `kill' has a meaning different from its usual meaning. The body of the function starts with an @code{if} clause. What this clause does is distinguish between two different situations: whether or not this command is executed immediately after a previous @code{kill-region} command. In the first case, the new region is appended to the previously copied text. Otherwise, it is inserted into the beginning of the kill ring as a separate piece of text from the previous piece. The last two lines of the function are two @code{setq} expressions. One of them sets the variable @code{this-command} to @code{kill-region} and the other sets the variable @code{kill-ring-yank-pointer} to point to the kill ring. The body of @code{copy-region-as-kill} merits discussion in detail. @menu * copy-region-as-kill body:: The body of @code{copy-region-as-kill} @end menu @node copy-region-as-kill body, , copy-region-as-kill, copy-region-as-kill @comment node-name, next, previous, up @subsection The Body of @code{copy-region-as-kill} The @code{copy-region-as-kill} function is written so that two or more kills in a row combine their text into a single entry. If you yank back the text from the kill ring, you get it all in one piece. Moreover, kills that kill forward from the current position of the cursor are added to the end of the previously copied text and commands that copy text backwards add it to the beginning of the previously copied text. This way, the words in the text stay in the proper order. The function makes use of two variables that keep track of the current and previous Emacs command. The two variables are @code{this-command} and @code{last-command}. Normally, whenever a function is executed, Emacs sets the value of @code{this-command} to the function being executed (which in this case would be @code{copy-region-as-kill}). At the same time, Emacs sets the value of @code{last-command} to the previous value of @code{this-command}. However, the @code{copy-region-as-kill} command is different; it sets the value of @code{this-command} to @code{kill-region}, which is the name of the function that calls @code{copy-region-as-kill}. In the first part of the body of the @code{copy-region-as-kill} function, an @code{if} expression determines whether the value of @code{last-command} is @code{kill-region}. If so, the then-part of the @code{if} expression is evaluated; it uses the @code{kill-append} function to concatenate the text copied at this call to the function with the text already in the first element (the @sc{car}) of the kill ring. On the other hand, if the value of @code{last-command} is not @code{kill-region}, then the @code{copy-region-as-kill} function attaches a new element to the kill ring. @need 1250 The @code{if} expression reads as follows; it uses @code{eq}, which is a function we have not yet seen: @example @group (if (eq last-command 'kill-region) ;; @r{then-part} (kill-append (buffer-substring beg end) (< end beg)) @end group @end example @findex eq @r{(example of use)} @noindent The @code{eq} function tests whether its first argument is the same Lisp object as its second argument. The @code{eq} function is similar to the @code{equal} function in that it is used to test for equality, but differs in that it determines whether two representations are actually the same object inside the computer, but with different names. @code{equal} determines whether the structure and contents of two expressions are the same. @menu * kill-append function:: The @code{kill-append} function * copy-region-as-kill else-part:: The else-part of @code{copy-region-as-kill} @end menu @node kill-append function, copy-region-as-kill else-part, copy-region-as-kill body, copy-region-as-kill body @unnumberedsubsubsec The @code{kill-append} function @findex kill-append The @code{kill-append} function looks like this: @example @group (defun kill-append (string before-p) (setcar kill-ring (if before-p (concat string (car kill-ring)) (concat (car kill-ring) string)))) @end group @end example We can look at this function in parts. The @code{setcar} function uses @code{concat} to concatenate the new text to the @sc{car} of the kill ring. Whether it prepends or appends the text depends on the results of an @code{if} expression: @example @group (if before-p ; @r{if-part} (concat string (car kill-ring)) ; @r{then-part} (concat (car kill-ring) string)) ; @r{else-part} @end group @end example @noindent If the region being killed is before the region that was killed in the last command, then it should be prepended before the material that was saved in the previous kill; and conversely, if the killed text follows what was just killed, it should be appended after the previous text. The @code{if} expression depends on the predicate @code{before-p} to decide whether the newly saved text should be put before or after the previously saved text. The symbol @code{before-p} is the name of one of the arguments to @code{kill-append}. When the @code{kill-append} function is evaluated, it is bound to the value returned by evaluating the actual argument. In this case, this is the expression @code{(< end beg)}. This expression does not directly determine whether the killed text in this command is located before or after the kill text of the last command; what is does is determine whether the value of the variable @code{end} is less than the value of the variable @code{beg}. If it is, it means that the user is most likely heading towards the beginning of the buffer. Also, the result of evaluating the predicate expression, @code{(< end beg)}, will be true and the text will be prepended before the previous text. On the other hand, if the value of the variable @code{end} is greater than the value of the variable @code{beg}, the text will be appended after the previous text. When the newly saved text will be prepended, then the string with the new text will be concatenated before the old test: @example (concat string (car kill-ring)) @end example @noindent But if the text will be appended, it will be concatenated after the old text: @example (concat (car kill-ring) string)) @end example To understand how this works, we first need to review the @code{concat} function. The @code{concat} function links together or unites two strings of text. The result is a string. For example: @example @group (concat "abc" "def") @result{} "abcdef" @end group @group (concat "new " (car '("first element" "second element"))) @result{} "new first element" (concat (car '("first element" "second element")) " modified") @result{} "first element modified" @end group @end example We can now make sense of @code{kill-append}: it modifies the contents of the kill ring. The kill ring is a list, each element of which is saved text. The @code{setcar} function actually changes the first element of this list. It does this by using @code{concat} to replace the old first element of the kill ring (the @sc{car} of the kill ring) with a new first element made by concatenating together the old saved text and the newly saved text. The newly saved text is put in front of the old text or after the old text, depending on whether it is in front of or after the old text in the buffer from which it is cut. The whole concatenation becomes the new first element of the kill ring. Incidentally, this is what the beginning of my current kill ring looks like: @example ("concatenating together" "saved text" "element" @dots{} @end example @node copy-region-as-kill else-part, , kill-append function, copy-region-as-kill body @unnumberedsubsubsec The else-part of @code{copy-region-as-kill} Now, back to the explanation of @code{copy-region-as-kill}: @need 1500 If the last command is not @code{kill-region}, then instead of calling @code{kill-append}, it calls the else-part of the following code: @example @group (if @var{true-or-false-test} @var{what-is-done-if-test-returns-true} ;; @r{else-part} (setq kill-ring (cons (buffer-substring beg end) kill-ring)) (if (> (length kill-ring) kill-ring-max) (setcdr (nthcdr (1- kill-ring-max) kill-ring) nil))) @end group @end example The @code{setq} line of the else-part sets the new value of the kill ring to what results from adding the string being killed to the old kill ring. We can see how this works with a little example: @example (setq example-list '("here is a clause" "another clause")) @end example @noindent After evaluating this expression with @kbd{C-x C-e}, you can evaluate @code{example-list} and see what it returns: @example @group example-list @result{} ("here is a clause" "another clause") @end group @end example @noindent Now, we can add a new element on to this list by evaluating the following expression: @example (setq example-list (cons "a third clause" example-list)) @end example @noindent When we evaluate @code{example-list}, we find its value is: @smallexample @group example-list @result{} ("a third clause" "here is a clause" "another clause") @end group @end smallexample @noindent Thus, the third clause was added to the list by @code{cons}. This is exactly similar to what the @code{setq} and @code{cons} do in the function, except that @code{buffer-substring} is used to pull out a copy of a region of text and hand it to the @code{cons}. Here is the line again: @example (setq kill-ring (cons (buffer-substring beg end) kill-ring)) @end example The next segment of the else-part of @code{copy-region-as-kill} is another @code{if} clause. This @code{if} clause keeps the kill ring from growing too long. It reads as follows: @example @group (if (> (length kill-ring) kill-ring-max) (setcdr (nthcdr (1- kill-ring-max) kill-ring) nil))) @end group @end example This code checks whether the length of the kill ring is greater than the maximum permitted length. This is the value of @code{kill-ring-max} (which is 30, by default). If the length of the kill ring is too long, then this code sets the last element of the kill ring to @code{nil}. It does this by using two functions, @code{nthcdr} and @code{setcdr}. We looked at @code{setcdr} earlier (@pxref{setcdr, , @code{setcdr}}). It sets the @sc{cdr} of a list, just as @code{setcar} sets the @sc{car} of a list. In this case, however, @code{setcdr} will not be setting the @code{cdr} of the whole kill ring; the @code{nthcdr} function is used to cause it to set the @code{cdr} of the next to last element of the kill ring---this means that since the @code{cdr} of the next to last element is the last element of the kill ring, it will set the last element of the kill ring. The @code{nthcdr} function works by repeatedly taking the @sc{cdr} of a list---it takes the @sc{cdr} of the @sc{cdr} of the @sc{cdr} @dots{} It does this @var{N} times and returns the results. Thus, if we had a four element list that was supposed to be three elements long, we could set the @sc{cdr} of the next to last element to @code{nil}, and thereby shorten the list. You can see this by evaluating the following three expressions in turn. First set the value of @code{trees} to @code{(maple oak pine birch)}, then set the @sc{cdr} of its second @sc{cdr} to @code{nil} and then find the value of @code{trees}: @example @group (setq trees '(maple oak pine birch)) @result{} (maple oak pine birch) @end group @group (setcdr (nthcdr 2 trees) nil) @result{} nil trees @result{} (maple oak pine) @end group @end example @noindent (The value returned by the @code{setcdr} expression is @code{nil} since that is what the @sc{cdr} is set to.) To repeat, in @code{copy-region-as-kill}, the @code{nthcdr} function takes the @sc{cdr} a number of times that is one less than the maximum permitted size of the kill ring and sets the @sc{cdr} of that element (which will be the rest of the elements in the kill ring) to @code{nil}. This prevents the kill ring from growing too long. The next to last line of the @code{copy-region-as-kill} function is @example @code{(setq this-command 'kill-region)} @end example @noindent This line is not part of either the inner or the outer @code{if} expression, so it is evaluated every time @code{copy-region-as-kill} is called. Here we find the place where @code{this-command} is set to @code{kill-region}. As we saw earlier, when the next command is given, the variable @code{last-command} will be given this value. @need 1250 Finally, the last line of the @code{copy-region-as-kill} function is: @example (setq kill-ring-yank-pointer kill-ring) @end example The @code{kill-ring-yank-pointer} is a global variable that is set to be the @code{kill-ring}. Even though the @code{kill-ring-yank-pointer} is called a @samp{pointer}, it is a variable just like the kill ring. However, the name has been chosen to help humans understand how the variable is used. The variable is used in functions such as @code{yank} and @code{yank-pop} (@pxref{Yanking, , Yanking Text Back}). This leads us to the code for bringing back text that has been cut out of the buffer---the yank commands. However, before discussing the yank commands, it is better to learn how lists are implemented in a computer. This will make clear such mysteries as the use of the term `pointer'. @node cons & search-fwd Review, search Exercises, copy-region-as-kill, Cutting & Storing Text @comment node-name, next, previous, up @section Review Here is a brief summary of some recently introduced functions. @table @code @item car @itemx cdr @code{car} returns the first element of a list; @code{cdr} returns the second and subsequent elements of a list. @need 1250 For example: @example @group (car '(1 2 3 4 5 6 7)) @result{} 1 (cdr '(1 2 3 4 5 6 7)) @result{} (2 3 4 5 6 7) @end group @end example @item cons @code{cons} constructs a list by prepending its first argument to its second argument. @need 1250 For example: @example @group (cons 1 '(2 3 4)) @result{} (1 2 3 4) @end group @end example @item nthcdr Return the result of taking @code{cdr} `n' times on a list. The `rest of the rest' as it were. @need 1250 For example: @example @group (nthcdr 3 '(1 2 3 4 5 6 7)) @result{} (4 5 6 7) @end group @end example @item setcar @itemx setcdr @code{setcar} changes the first element of a list; @code{setcdr} changes the second and subsequent elements of a list. @need 1250 For example: @example @group (setq triple '(1 2 3)) (setcar triple '37) triple @result{} (37 2 3) (setcdr triple '("foo" "bar")) triple @result{} (37 "foo" "bar") @end group @end example @item progn Evaluate each argument in sequence and then return the value of the last. @need 1250 For example: @example @group (progn 1 2 3 4) @result{} 4 @end group @end example @item save-restriction Record whatever narrowing is in effect in the current buffer, if any, and restore that narrowing after evaluating the arguments. @item search-forward Search for a string, and if the string is found, move point. @noindent Takes four arguments: @enumerate @item The string to search for. @item Optionally, the limit of the search. @item Optionally, what to do if the search fails, return @code{nil} or an error message. @item Optionally, how many times to repeat the search; if negative, the search goes backwards. @end enumerate @item kill-region @itemx delete-region @itemx copy-region-as-kill @code{kill-region} cuts the text between point and mark from the buffer and stores that text in the kill ring, so you can get it back by yanking. @code{delete-region} removes the text between point and mark from the buffer and throws it away. You cannot get it back. @code{copy-region-as-kill} copies the text between point and mark into the kill ring, from which you can get it by yanking. The function does not cut or remove the text from the buffer. @end table @need 1500 @node search Exercises, , cons & search-fwd Review, Cutting & Storing Text @section Searching Exercises @itemize @bullet @item Write an interactive function that searches for a string. If the search find the string, leave point after it and display a message that says ``Found!''. (Do not use @code{search-forward} for the name of this function; if you do, you will overwrite the existing version of @code{search-forward} that comes with Emacs. Use a name such as @code{test-search} instead.) @item Write a function that prints the third element of the kill ring in the echo area, if any; if the kill ring does not contain a third element, print an appropriate message. @item As of version 19.29, @code{copy-region-as-kill} no longer sets @code{this-command}. What are the consequences of this change? What do you suppose motivated it? @end itemize @node List Implementation, Yanking, Cutting & Storing Text, Top @comment node-name, next, previous, up @chapter How Lists are Implemented @cindex Lists in a computer In Lisp, atoms are recorded in a straightforward fashion; if the implementation is not straightforward in practice, it is, nonetheless, straightforward in theory. The atom @samp{rose}, for example, is recorded as the four contiguous letters @samp{r}, @samp{o}, @samp{s}, @samp{e}. A list, on the other hand, is kept differently. The mechanism is equally simple, but it takes a moment to get used to the idea. A list is kept using a series of pairs of pointers. In the series, the first pointer in each pair points to an atom or to another list, and the second pointer in each pair points to the next pair, or to the symbol @code{nil}, which marks the end of the list. A pointer itself is quite simply the electronic address of what is pointed to. Hence, a list is kept as a series of electronic addresses. For example, the list @code{(rose violet buttercup)} has three elements, @samp{rose}, @samp{violet}, and @samp{buttercup}. In the computer, the electronic address of @samp{rose} is recorded in a segment of computer memory along with the address that gives the electronic address of where the atom @samp{violet} is located; and that address (the one that tells where @samp{violet} is located) is kept along with an address that tells where the address for the atom @samp{buttercup} is located. This sounds more complicated than it is and is easier seen in a diagram: @c clear print-postscript-figures @c !!! cons-cell-diagram #1 @ifinfo @example @group ___ ___ ___ ___ ___ ___ |___|___|--> |___|___|--> |___|___|--> nil | | | | | | --> rose --> violet --> buttercup @end group @end example @end ifinfo @ifset print-postscript-figures @sp 1 @tex \input /usr/local/lib/tex/inputs/psfig.tex \centerline{\psfig{figure=/usr/local/lib/emacs/man/cons-cell-diagram1.eps}} \catcode`\@=0 % @end tex @sp 1 @end ifset @ifclear print-postscript-figures @iftex @example @group ___ ___ ___ ___ ___ ___ |___|___|--> |___|___|--> |___|___|--> nil | | | | | | --> rose --> violet --> buttercup @end group @end example @end iftex @end ifclear @noindent In the diagram, each box represents a word of computer memory that holds a Lisp object, usually in the form of a memory address. The boxes, i.e.@: the addresses, are in pairs. Each arrow points to what the address is the address of, either an atom or another pair of addresses. The first box is the electronic address of @samp{rose} and the arrow points to @samp{rose}; the second box is the address of the next pair of boxes, the first part of which is the address of @samp{violet} and the second part of which is the address of the next pair. The very last box points to the symbol @code{nil}, which marks the end of the list. When a variable is set to a list with a function such as @code{setq}, it stores the address of the first box in the variable. Thus, evaluation of the expression @example (setq bouquet '(rose violet buttercup)) @end example @need 1250 @noindent creates a situation like this: @c cons-cell-diagram #2 @ifinfo @example @group bouquet | | ___ ___ ___ ___ ___ ___ --> |___|___|--> |___|___|--> |___|___|--> nil | | | | | | --> rose --> violet --> buttercup @end group @end example @end ifinfo @ifset print-postscript-figures @sp 1 @tex \input /usr/local/lib/tex/inputs/psfig.tex \centerline{\psfig{figure=/usr/local/lib/emacs/man/cons-cell-diagram2.eps}} \catcode`\@=0 % @end tex @sp 1 @end ifset @ifclear print-postscript-figures @iftex @example @group bouquet | | ___ ___ ___ ___ ___ ___ --> |___|___|--> |___|___|--> |___|___|--> nil | | | | | | --> rose --> violet --> buttercup @end group @end example @end iftex @end ifclear @noindent In this case, the symbol @code{bouquet} holds the address of the first pair of boxes. Indeed, the symbol @code{bouquet} consists of a group of address-boxes, one of which is the address of the printed word @samp{bouquet}, a second of which is the address of a function definition attached to the symbol, if any, a third of which is the address of the first pair of address-boxes for the list @code{(rose violet buttercup)}, and so on. This same list can be illustrated in a different sort of box notation like this: @c cons-cell-diagram #2a @ifinfo @smallexample @group bouquet | | -------------- --------------- ---------------- | | car | cdr | | car | cdr | | car | cdr | -->| rose | o------->| violet | o------->| butter- | nil | | | | | | | | cup | | -------------- --------------- ---------------- @end group @end smallexample @end ifinfo @ifset print-postscript-figures @sp 1 @tex \input /usr/local/lib/tex/inputs/psfig.tex \centerline{\psfig{figure=/usr/local/lib/emacs/man/cons-cell-diagram2a.eps}} \catcode`\@=0 % @end tex @sp 1 @end ifset @ifclear print-postscript-figures @iftex @smallexample @group bouquet | | -------------- --------------- ---------------- | | car | cdr | | car | cdr | | car | cdr | -->| rose | o------->| violet | o------->| butter- | nil | | | | | | | | cup | | -------------- --------------- ---------------- @end group @end smallexample @end iftex @end ifclear In an earlier section, I suggested that you might imagine a symbol as being a chest of drawers. The function definition is put in one drawer, the value in another, and so on. What is put in the drawer holding the value can be changed without affecting the contents of the drawer holding the function definition, and vice-versa. Actually, what is put in each drawer is the address of the value or function definition. It is as if you found an old chest in the attic, and in one of its drawers you found a map giving you directions to where the buried treasure lies. (In addition to its name, symbol definition, and variable value, a symbol has a `drawer' for a @dfn{property list} which can be used to record other information. Property lists are not discussed here; see @ref{Property Lists, , Property Lists, elisp, The GNU Emacs Lisp Reference Manual}.) @need 1500 Here is a fanciful representation: @c chest-of-drawers diagram @ifinfo @sp 1 @smallexample @group Chest of Drawers Contents of Drawers --------------------- | | | symbol name | bouquet | | --------------------- | | | symbol definition | [none] | | --------------------- | | | variable value | (rose violet buttercup) | | --------------------- | | | property list | [not described here] | | --------------------- |/ \| @end group @end smallexample @sp 1 @end ifinfo @ifset print-postscript-figures @sp 1 @tex \input /usr/local/lib/tex/inputs/psfig.tex \centerline{\psfig{figure=/usr/local/lib/emacs/man/chest-of-drawers-diagram.eps}} \catcode`\@=0 % @end tex @sp 1 @end ifset @ifclear print-postscript-figures @iftex @sp 1 @smallexample @group Chest of Drawers Contents of Drawers --------------------- | | | symbol name | bouquet | | --------------------- | | | symbol definition | [none] | | --------------------- | | | variable value | (rose violet buttercup) | | --------------------- | | | property list | [not described here] | | --------------------- |/ \| @end group @end smallexample @sp 1 @end iftex @end ifclear If symbol is set to the @sc{cdr} of a list, the list itself is not changed; the symbol simply has an address further down the list. (In the jargon, @sc{car} and @sc{cdr} are `non-destructive'.) Thus, evaluation of the following expression @example (setq flowers (cdr bouquet)) @end example @noindent produces this: @c cons-cell-diagram #3 @ifinfo @sp 1 @example @group bouquet flowers | | | ___ ___ | ___ ___ ___ ___ --> | | | --> | | | | | | |___|___|----> |___|___|--> |___|___|--> nil | | | | | | --> rose --> violet --> buttercup @end group @end example @sp 1 @end ifinfo @ifset print-postscript-figures @sp 1 @tex \input /usr/local/lib/tex/inputs/psfig.tex \centerline{\psfig{figure=/usr/local/lib/emacs/man/cons-cell-diagram3.eps}} \catcode`\@=0 % @end tex @sp 1 @end ifset @ifclear print-postscript-figures @iftex @sp 1 @example @group bouquet flowers | | | ___ ___ | ___ ___ ___ ___ --> | | | --> | | | | | | |___|___|----> |___|___|--> |___|___|--> nil | | | | | | --> rose --> violet --> buttercup @end group @end example @sp 1 @end iftex @end ifclear @noindent The value of @code{flowers} is @code{(violet buttercup)}, which is to say, the symbol @code{flowers} holds the address of the pair of address-boxes, the first of which holds the address of @code{violet}, and the second of which holds the address of @code{buttercup}. A pair of address-boxes is called a @dfn{cons cell} or @dfn{dotted pair}. @xref{List Type, , List Type , elisp, The GNU Emacs Lisp Reference Manual}, and @ref{Dotted Pair Notation, , Dotted Pair Notation, elisp, The GNU Emacs Lisp Reference Manual}, for more information about cons cells and dotted pairs. The function @code{cons} adds a new pair of addresses to the front of a series of addresses like that shown above. For example, evaluating the expression @example (setq bouquet (cons 'lilly bouquet)) @end example @noindent produces: @c cons-cell-diagram #4 @ifinfo @sp 1 @example @group bouquet flowers | | | ___ ___ ___ ___ | ___ ___ ___ ___ --> | | | | | | --> | | | | | | |___|___|----> |___|___|----> |___|___|---->|___|___|--> nil | | | | | | | | --> lilly --> rose --> violet --> buttercup @end group @end example @sp 1 @end ifinfo @ifset print-postscript-figures @sp 1 @tex \input /usr/local/lib/tex/inputs/psfig.tex \centerline{\psfig{figure=/usr/local/lib/emacs/man/cons-cell-diagram4.eps}} \catcode`\@=0 % @end tex @sp 1 @end ifset @ifclear print-postscript-figures @iftex @sp 1 @smallexample @group bouquet flowers | | | ___ ___ ___ ___ | ___ ___ ___ ___ --> | | | | | | --> | | | | | | |___|___|----> |___|___|----> |___|___|---->|___|___|--> nil | | | | | | | | --> lilly --> rose --> violet --> buttercup @end group @end smallexample @sp 1 @end iftex @end ifclear @noindent However, this does not change the value of the symbol @code{flowers}, as you can see by evaluating the following, @example (eq (cdr (cdr bouquet)) flowers) @end example @noindent which returns @code{t} for true. Until it is reset, @code{flowers} still has the value @code{(violet buttercup)}; that is, it has the address of the cons cell whose first address is of @code{violet}. Also, this does not alter any of the pre-existing cons cells; they are all still there. Thus, in Lisp, to get the @sc{cdr} of a list, you just get the address of the next cons cell in the series; to get the @sc{car} of a list, you get the address of the first element of the list; to @code{cons} a new element on a list, you add a new cons cell to the front of the list. That is all there is to it! The underlying structure of Lisp is brilliantly simple! And what does the last address in a series of cons cells refer to? It is the address of the empty list, of @code{nil}. In summary, when a Lisp variable is set to a value, it is provided with the address of the list to which the variable refers. @menu * List Exercise:: @end menu @node List Exercise, , List Implementation, List Implementation @section Exercise Set @code{flowers} to @code{violet} and @code{buttercup}. Cons two more flowers on to this list and set this new list to @code{more-flowers}. Set the @sc{car} of @code{flowers} to a fish. What does the @code{more-flowers} list now contain? @node Yanking, Loops & Recursion, List Implementation, Top @comment node-name, next, previous, up @chapter Yanking Text Back @findex yank @findex rotate-yank-pointer @cindex Text retrieval @cindex Retrieving text @cindex Pasting text Whenever you cut text out of a buffer with a `kill' command in GNU Emacs, you can bring it back with a `yank' command. The text that is cut out of the buffer is put in the kill ring and the yank commands insert the appropriate contents of the kill ring back into a buffer (not necessarily the original buffer). A simple @kbd{C-y} (@code{yank}) command inserts the first item from the kill ring into the current buffer. If the @kbd{C-y} command is followed immediately by @kbd{M-y}, the first element is replaced by the second element. Successive @kbd{M-y} commands replace the second element with the third, fourth, or fifth element, and so on. When the last element in the kill ring is reached, it is replaced by the first element and the cycle is repeated. (Thus the kill ring is called a `ring' rather than just a `list'. However, the actual data structure that holds the text is a list. @xref{Kill Ring, , Handling the Kill Ring}, for the details of how the list is handled as a ring.) @menu * Kill Ring Overview:: The kill ring is a list. * kill-ring-yank-pointer:: The @code{kill-ring-yank-pointer} variable. * yank nthcdr Exercises:: @end menu @node Kill Ring Overview, kill-ring-yank-pointer, Yanking, Yanking @comment node-name, next, previous, up @section Kill Ring Overview @cindex Kill ring overview The kill ring is a list of textual strings. This is what it looks like: @example ("some text" "a different piece of text" "yet more text") @end example If this were the contents of my kill ring and I pressed @kbd{C-y}, the string of characters saying @samp{some text} would be inserted in this buffer where my cursor is located. The @code{yank} command is also used for duplicating text by copying it. The copied text is not cut from the buffer, but a copy of it is put on the kill ring and is inserted by yanking it back. Three functions are used for bringing text back from the kill ring: @code{yank}, which is usually bound to @kbd{C-y}; @code{yank-pop}, which is usually bound to @kbd{M-y}; and @code{rotate-yank-pointer}, which is used by the two other functions. These functions refer to the kill ring through a variable called the @code{kill-ring-yank-pointer}. Indeed, the insertion code for both the @code{yank} and @code{yank-pop} functions is: @example (insert (car kill-ring-yank-pointer)) @end example To begin to understand how @code{yank} and @code{yank-pop} work, it is first necessary to look at the @code{kill-ring-yank-pointer} variable and the @code{rotate-yank-pointer} function. @node kill-ring-yank-pointer, yank nthcdr Exercises, Kill Ring Overview, Yanking @comment node-name, next, previous, up @section The @code{kill-ring-yank-pointer} Variable @code{kill-ring-yank-pointer} is a variable, just as @code{kill-ring} is a variable. It points to something by being bound to the value of what it points to, like any other Lisp variable. @need 1000 Thus, if the value of the kill ring is: @example ("some text" "a different piece of text" "yet more text") @end example @need 1250 @noindent and the @code{kill-ring-yank-pointer} points to the second clause, the value of @code{kill-ring-yank-pointer} is: @example ("a different piece of text" "yet more text") @end example As explained in the previous chapter (@pxref{List Implementation}), the computer does not keep two different copies of the text being pointed to by both the @code{kill-ring} and the @code{kill-ring-yank-pointer}. The words ``a different piece of text'' and ``yet more text'' are not duplicated. Instead, the two Lisp variables point to the same pieces of text. Here is a diagram: @c cons-cell-diagram #5 @ifinfo @example @group kill-ring kill-ring-yank-pointer | | | ___ ___ | ___ ___ ___ ___ ---> | | | --> | | | | | | |___|___|----> |___|___|--> |___|___|--> nil | | | | | | | | --> "yet more text" | | | --> "a different piece of text | --> "some text" @end group @end example @sp 1 @end ifinfo @ifset print-postscript-figures @sp 1 @tex \input /usr/local/lib/tex/inputs/psfig.tex \centerline{\psfig{figure=/usr/local/lib/emacs/man/cons-cell-diagram5.eps}} \catcode`\@=0 % @end tex @sp 1 @end ifset @ifclear print-postscript-figures @iftex @example @group kill-ring kill-ring-yank-pointer | | | ___ ___ | ___ ___ ___ ___ ---> | | | --> | | | | | | |___|___|----> |___|___|--> |___|___|--> nil | | | | | | | | --> "yet more text" | | | --> "a different piece of text | --> "some text" @end group @end example @sp 1 @end iftex @end ifclear Both the variable @code{kill-ring} and the variable @code{kill-ring-yank-pointer} are pointers. But the kill ring itself is usually described as if it were actually what it is composed of. The @code{kill-ring} is spoken of as if it were the list rather than that it points to the list. Conversely, the @code{kill-ring-yank-pointer} is spoken of as pointing to a list. These two ways of talking about the same thing sound confusing at first but make sense on reflection. The kill ring is generally thought of as the complete structure of data that holds the information of what has recently been cut out of the Emacs buffers. The @code{kill-ring-yank-pointer} on the other hand, serves to indicate---that is, to `point to'---that part of the kill ring of which the first element (the @sc{car}) will be inserted. The @code{rotate-yank-pointer} function changes the element in the kill ring to which the @code{kill-ring-yank-pointer} points; when the pointer is set to point to the next element beyond the end of the kill ring, it automatically sets it to point to the first element of the kill ring. This is how the list is transformed into a ring. The @code{rotate-yank-pointer} function itself is not difficult, but contains many details. It and the much simpler @code{yank} and @code{yank-pop} functions are described in an appendix. @xref{Kill Ring, , Handling the Kill Ring}. @need 1500 @node yank nthcdr Exercises, , kill-ring-yank-pointer, Yanking @section Exercises with @code{yank} and @code{nthcdr} @itemize @bullet @item Using @kbd{C-h v} (@code{describe-variable}), look at the value of your kill ring. Add several items to your kill ring; look at its value again. Using @kbd{M-y} (@code{yank-pop)}, move all the way around the kill ring. How many items were in your kill ring? Find the value of @code{kill-ring-max}. Was your kill ring full, or could you have kept more blocks of text within it? @item Using @code{nthcdr} and @code{car}, construct a series of expressions to return the first, second, third, and fourth elements of a list. @end itemize @node Loops & Recursion, Regexp Search, Yanking, Top @comment node-name, next, previous, up @chapter Loops and Recursion @cindex Loops and recursion @cindex Recursion and loops @cindex Repetition (loops) Emacs Lisp has two primary ways to cause an expression, or a series of expressions, to be evaluated repeatedly: one uses a @code{while} loop, and the other uses @dfn{recursion}. Repetition can be very valuable. For example, to move forward four sentences, you need only write a program that will move forward one sentence and then repeat the process four times. Since a computer does not get bored or tired, such repetitive action does not have the deleterious effects that excessive or the wrong kinds of repetition can have on humans. @menu * while:: Causing a stretch of code to repeat. * Recursion:: Causing a function to call itself. * Looping exercise:: @end menu @node while, Recursion, Loops & Recursion, Loops & Recursion @comment node-name, next, previous, up @section @code{while} @cindex Loops @findex while The @code{while} special form tests whether the value returned by evaluating its first argument is true or false. This is similar to what the Lisp interpreter does with an @code{if}; what the interpreter does next, however, is different. In a @code{while} expression, if the value returned by evaluating the first argument is false, the Lisp interpreter skips the rest of the expression (the @dfn{body} of the expression) and does not evaluate it. However, if the value is true, the Lisp interpreter evaluates the body of the expression and then again tests whether the first argument to @code{while} is true or false. If the value returned by evaluating the first argument is again true, the Lisp interpreter again evaluates the body of the expression. The template for a @code{while} expression looks like this: @example @group (while @var{true-or-false-test} @var{body}@dots{}) @end group @end example So long as the true-or-false-test of the @code{while} expression returns a true value when it is evaluated, the body is repeatedly evaluated. This process is called a loop since the Lisp interpreter repeats the same thing again and again, like an airplane doing a loop. When the result of evaluating the true-or-false-test is false, the Lisp interpreter does not evaluate the rest of the @code{while} expression and `exits the loop'. Clearly, if the value returned by evaluating the first argument to @code{while} is always true, the body following will be evaluated again and again @dots{} and again @dots{} forever. Conversely, if the value returned is never true, the expressions in the body will never be evaluated. The craft of writing a @code{while} loop consists of choosing a mechanism such that the true-or-false-test returns true just the number of times that you want the subsequent expressions to be evaluated, and then have the test return false. The value returned by evaluating a @code{while} is the value of the true-or-false-test. An interesting consequence of this is that a @code{while} loop that evaluates without error will return @code{nil} or false regardless of whether it has looped 1 or 100 times or none at all. A @code{while} expression that evaluates successfully never returns a true value! What this means is that @code{while} is always evaluated for its side effects, which is to say, the consequences of evaluating the expressions within the body of the @code{while} loop. This makes sense. It is not the mere act of looping that is desired, but the consequences of what happens when the expressions in the loop are repeatedly evaluated. @menu * Loop Example:: A @code{while} loop that uses a list. * print-elements-of-list:: Uses @code{while}, @code{car}, @code{cdr}. * Incrementing Loop:: A loop with an incrementing counter. * Decrementing Loop:: A loop with a decrementing counter. @end menu @node Loop Example, print-elements-of-list, while, while @comment node-name, next, previous, up @subsection A @code{while} Loop and a List A common way to control a @code{while} loop is to test whether a list has any elements. If it does, the loop is repeated; but if it does not, the repetition is ended. Since this is an important technique, we will create a short example to illustrate it. A simple way to test whether a list has elements is to evaluate the list: if it has no elements, it is an empty list and will return the empty list, @code{()}, which is a synonym for @code{nil} or false. On the other hand, a list with elements will return those elements when it is evaluated. Since Lisp considers as true any value that is not @code{nil}, a list that returns elements will test true in a @code{while} loop. For example, you can set the variable @code{empty-list} to @code{nil} by evaluating the following @code{setq} expression: @example (setq empty-list ()) @end example @noindent After evaluating the @code{setq} expression, you can evaluate the variable @code{empty-list} in the usual way, by placing the cursor after the symbol and typing @kbd{C-x C-e}; @code{nil} will appear in your echo area: @example empty-list @end example On the other hand, if you set a variable to be a list with elements, the list will appear when you evaluate the variable, as you can see by evaluating the following two expressions: @example @group (setq animals '(giraffe gazelle lion tiger)) animals @end group @end example Thus, to create a @code{while} loop that tests whether there are any items in the list @code{animals}, the first part of the loop will be written like this: @example @group (while animals @dots{} @end group @end example @noindent When the @code{while} tests its first argument, the variable @code{animals} is evaluated. It returns a list. So long as the list has elements, the @code{while} considers the results of the test to be true; but when the list is empty, considers the results of the test to be false. To prevent the @code{while} loop from running forever, some mechanism needs to be provided to empty the list eventually. An oft-used technique is to have one of the subsequent forms in the @code{while} expression set the value of the list to be the @sc{cdr} of the list. Each time the @code{cdr} function is evaluated, the list will be made shorter, until eventually only the empty list will be left. At this point, the test of the @code{while} loop will return false, and the arguments to the @code{while} will no longer be evaluated. For example, the list of animals bound to the variable @code{animals} can be set to be the @sc{cdr} of the original list with the following expression: @example (setq animals (cdr animals)) @end example @noindent If you have evaluated the previous expressions and then evaluate this expression, you will see @code{(gazelle lion tiger)} appear in the echo area. If you evaluate the expression again, @code{(lion tiger)} will appear in the echo area. If you evaluate it again and yet again, @code{(tiger)} appears and then the empty list, shown by @code{nil}. A template for a @code{while} loop that uses the @code{cdr} function repeatedly to cause the true-or-false-test eventually to test false looks like this: @example @group (while @var{test-whether-list-is-empty} @var{body}@dots{} @var{set-list-to-cdr-of-list}) @end group @end example This test and use of @code{cdr} can be put together in a function that goes through a list and prints each element of the list on a line of its own. @node print-elements-of-list, Incrementing Loop, Loop Example, while @subsection An Example: @code{print-elements-of-list} @findex print-elements-of-list The @code{print-elements-of-list} function illustrates a @code{while} loop with a list. @cindex @file{*scratch*} buffer The function requires several lines for its output. Since the echo area is only one line, we cannot illustrate how it works in the same way we have been illustrating functions in the past, by evaluating them inside Info. Instead, you need to copy the necessary expressions to your @file{*scratch*} buffer and evaluate them there. You can copy the expressions by marking the beginning of the region with @kbd{C-@key{SPC}} (@code{set-mark-command}), moving the cursor to the end of the region and then copying the region using @kbd{M-w} (@code{copy-region-as-kill}). In the @file{*scratch*} buffer, you can yank the expressions back by typing @kbd{C-y} (@code{yank}). After you have copied the expressions to the @file{*scratch*} buffer, evaluate each expression in turn. Be sure to evaluate the last expression, @code{(print-elements-of-list animals)}, by typing @kbd{C-u C-x C-e}, that is, by giving an argument to @code{eval-last-sexp}. This will cause the result of the evaluation to be printed in the @file{*scratch*} buffer instead of being printed in the echo area. (Otherwise you will see something like this in your echo area: @code{^Jgiraffe^J^Jgazelle^J^Jlion^J^Jtiger^Jnil}, in which each @samp{^J} stands for the newline that in the @file{*scratch*} buffer puts each word on its own line. You can evaluate these expressions right now in the Info buffer, if you like, to see this effect.) @example @group (setq animals '(giraffe gazelle lion tiger)) (defun print-elements-of-list (list) "Print each element of LIST on a line of its own." (while list (print (car list)) (setq list (cdr list)))) (print-elements-of-list animals) @end group @end example @noindent When you evaluate the three expressions in sequence in the @file{*scratch*} buffer, this will be printed in the buffer: @example @group giraffe gazelle lion tiger nil @end group @end example Each element of the list is printed on a line of its own (that is what the function @code{print} does) and then the value returned by the function is printed. Since the last expression in the function is the @code{while} loop, and since @code{while} loops always return @code{nil}, a @code{nil} is printed after the last element of the list. @node Incrementing Loop, Decrementing Loop, print-elements-of-list, while @comment node-name, next, previous, up @subsection A Loop with an Incrementing Counter A loop is not useful unless it stops when it ought. Besides controlling a loop with a list, a common way of stopping a loop is to write the first argument as a test that returns false when the correct number of repetitions are complete. This means that the loop must have a counter---an expression that counts how many times the loop repeats itself. The test can be an expression such as @code{(< count desired-number)} which returns @code{t} for true if the value of @code{count} is less than the @code{desired-number} of repetitions and @code{nil} for false if the value of @code{count} is equal to or is greater than the @code{desired-number}. The expression that increments the count can be a simple @code{setq} such as @code{(setq count (1+ count))}, where @code{1+} is a built-in function in Emacs Lisp that adds 1 to its argument. (The expression @code{(1+ count)} has the same result as @code{(+ count 1)}, but is easier for a human to read.) The template for a @code{while} loop controlled by an incrementing counter looks like this: @example @group @var{set-count-to-initial-value} (while (< count desired-number) ; @r{true-or-false-test} @var{body}@dots{} (setq count (1+ count))) ; @r{incrementer} @end group @end example @noindent Note that you need to set the initial value of @code{count}; usually it is set to 1. @menu * Incrementing Example:: Counting pebbles in a triangle. * Inc Example parts:: The parts of the function definition. * Inc Example altogether:: Putting the function definition together. @end menu @node Incrementing Example, Inc Example parts, Incrementing Loop, Incrementing Loop @unnumberedsubsubsec Example with incrementing counter Suppose you are playing on the beach and decide to make a triangle of pebbles, putting one pebble in the first row, two in the second row, three in the third row and so on, like this: @sp 1 @c pebble diagram @ifinfo @example @group * * * * * * * * * * @end group @end example @end ifinfo @iftex @example @group @bullet{} @bullet{} @bullet{} @bullet{} @bullet{} @bullet{} @bullet{} @bullet{} @bullet{} @bullet{} @end group @end example @end iftex @sp 1 @noindent (About 2500 years ago, Pythagoras and others developed the beginnings of number theory by considering questions such as this.) Suppose you want to know how many pebbles you will need to make a triangle with 7 rows? Clearly, what you need to do is add up the numbers from 1 to 7. There are two ways to do this; start with the smallest number, one, and add up the list in sequence, 1, 2, 3, 4 and so on; or start with the largest number and add the list going down: 7, 6, 5, 4 and so on. Because both mechanisms illustrate common ways of writing @code{while} loops, we will create two examples, one counting up and the other counting down. In this first example, we will start with 1 and add 2, 3, 4 and so on. If you are just adding up a short list of numbers, the easiest way to do it is to add up all the numbers at once. However, if you do not know ahead of time how many numbers your list will have, or if you want to be prepared for a very long list, then you need to design your addition so that what you do is repeat a simple process many times instead of doing a more complex process once. For example, instead of adding up all the pebbles all at once, what you can do is add the number of pebbles in the first row, 1, to the number in the second row, 2, and then add the total of those two rows to the third row, 3. Then you can add the number in the fourth row, 4, to the total of the first three rows; and so on. The critical characteristic of the process is that each repetitive action is simple. In this case, at each step we add only two numbers, the number of pebbles in the row and the total already found. This process of adding two numbers is repeated again and again until the last row has been added to the total of all the preceding rows. In a more complex loop the repetitive action might not be so simple, but it will be simpler than doing everything all at once. @node Inc Example parts, Inc Example altogether, Incrementing Example, Incrementing Loop @unnumberedsubsubsec The parts of the function definition The preceding analysis gives us the bones of our function definition: first, we will need a variable that we can call @code{total} that will be the total number of pebbles. This will be the value returned by the function. Second, we know that the function will require an argument: this argument will be the total number of rows in the triangle. It can be called @code{number-of-rows}. Finally, we need a variable to use as a counter. We could call this variable @code{counter}, but a better name is @code{row-number}. That is because what the counter does is count rows, and a program should be written to be understandable as possible. When the Lisp interpreter first starts evaluating the expressions in the function, the value of @code{total} should be set to zero, since we have not added anything to it. Then the function should add the number of pebbles in the first row to the total, and then add the number of pebbles in the second to the total, and then add the number of pebbles in the third row to the total, and so on, until there are no more rows left to add. Both @code{total} and @code{row-number} are used only inside the function, so they can be declared as local variables with @code{let} and given initial values. Clearly, the initial value for @code{total} should be 0. The initial value of @code{row-number} should be 1, since we start with the first row. This means that the @code{let} statement will look like this: @example @group (let ((total 0) (row-number 1)) @var{body}@dots{}) @end group @end example After the internal variables are declared and bound to their initial values, we can begin the @code{while} loop. The expression that serves as the test should return a value of @code{t} for true so long as the @code{row-number} is less than or equal to the @code{number-of-rows}. (If the expression tests true only so long as the row number is less than the number of rows in the triangle, the last row will never be added to the total; hence the row number has to be either less than or equal to the number of rows.) @findex <= @r{(less than or equal)} Lisp provides the @code{<=} function that returns true if the value of its first argument is less than or equal to the value of its second argument and false otherwise. So the expression that the @code{while} will evaluate as its test should look like this: @example (<= row-number number-of-rows) @end example The total number of pebbles can be found by repeatedly adding the number of pebbles in a row to the total already found. Since the number of pebbles in the row is equal to the row number, the total can be found by adding the row number to the total. (Clearly, in a more complex situation, the number of pebbles in the row might be related to the row number in a more complicated way; if this were the case, the row number would be replaced by the appropriate expression.) @example (setq total (+ total row-number)) @end example @noindent What this does is set the new value of @code{total} to be equal to the sum of adding the number of pebbles in the row to the previous total. After setting the value of @code{total}, the conditions need to be established for the next repetition of the loop, if there is one. This is done by incrementing the value of the @code{row-number} variable, which serves as a counter. After the @code{row-number} variable has been incremented, the true-or-false-test at the beginning of the @code{while} loop tests whether its value is still less than or equal to the value of the @code{number-of-rows} and if it is, adds the new value of the @code{row-number} variable to the @code{total} of the previous repetition of the loop. The built-in Emacs Lisp function @code{1+} adds 1 to a number, so the @code{row-number} variable can be incremented with this expression: @example (setq row-number (1+ row-number)) @end example @node Inc Example altogether, , Inc Example parts, Incrementing Loop @unnumberedsubsubsec Putting the function definition together We have created the parts for the function definition; now we need to put them together. First, the contents of the @code{while} expression: @example @group (while (<= row-number number-of-rows) ; @r{true-or-false-test} (setq total (+ total row-number)) (setq row-number (1+ row-number))) ; @r{incrementer} @end group @end example Along with the @code{let} expression varlist, this very nearly completes the body of the function definition. However, it requires one final element, the need for which is somewhat subtle. The final touch is to place the variable @code{total} on a line by itself after the @code{while} expression. Otherwise, the value returned by the whole function is the value of the last expression that is evaluated in the body of the @code{let}, and this is the value returned by the @code{while}, which is always @code{nil}. This may not be evident at first sight. It almost looks as if the incrementing expression is the last expression of the whole function. But that expression is part of the body of the @code{while}; it is the last element of the list that starts with the symbol @code{while}. Moreover, the whole of the @code{while} loop is a list within the body of the @code{let}. @need 1250 In outline, the function will look like this: @example @group (defun @var{name-of-function} (@var{argument-list}) "@var{documentation}@dots{}" (let (@var{varlist}) (while (@var{true-or-false-test}) @var{body-of-while}@dots{} ) @dots{} ) ; @r{Need final expression here.} @end group @end example The result of evaluating the @code{let} is what is going to be returned by the @code{defun} since the @code{let} is not embedded within any containing list, except for the @code{defun} as a whole. However, if the @code{while} is the last element of the @code{let} expression, the function will always return @code{nil}. This is not what we want! Instead, what we want is the value of the variable @code{total}. This is returned by simply placing the symbol as the last element of the list starting with @code{let}. It gets evaluated after the preceding elements of the list are evaluated, which means it gets evaluated after it has been assigned the correct value for the total. It may be easier to see this by printing the list starting with @code{let} all on one line. This format makes it evident that the @var{varlist} and @code{while} expressions are the second and third elements of the list starting with @code{let}, and the @code{total} is the last element: @example @group (let (@var{varlist}) (while (@var{true-or-false-test}) @var{body-of-while}@dots{} ) total) @end group @end example Putting everything together, the @code{triangle} function definition looks like this: @example @group (defun triangle (number-of-rows) ; @r{Version with} ; @r{ incrementing counter.} "Add up the number of pebbles in a triangle. The first row has one pebble, the second row two pebbles, the third row three pebbles, and so on. The argument is NUMBER-OF-ROWS." @end group @group (let ((total 0) (row-number 1)) (while (<= row-number number-of-rows) (setq total (+ total row-number)) (setq row-number (1+ row-number))) total)) @end group @end example After you have installed @code{triangle} by evaluating the function, you can try it out. Here are two examples: @example @group (triangle 4) (triangle 7) @end group @end example @noindent The sum of the first four numbers is 10 and the sum of the first seven numbers is 28. @node Decrementing Loop, , Incrementing Loop, while @comment node-name, next, previous, up @subsection Loop with a Decrementing Counter Another common way to write a @code{while} loop is to write the test so that it determines whether a counter is greater than zero. So long as the counter is greater than zero, the loop is repeated. But when the counter is equal to or less than zero, the loop is stopped. For this to work, the counter has to start out greater than zero and then be made smaller and smaller by one of the forms that is evaluated repeatedly. The test will be an expression such as @code{(> counter 0)} which returns @code{t} for true if the value of @code{counter} is greater than zero, and @code{nil} for false if the value of @code{counter} is equal to or less than zero. The expression that makes the number smaller and smaller can be a simple @code{setq} such as @code{(setq counter (1- counter))}, where @code{1-} is a built-in function in Emacs Lisp that subtracts 1 from its argument. @need 1250 The template for a decrementing @code{while} loop looks like this: @example @group (while (> counter 0) ; @r{true-or-false-test} @var{body}@dots{} (setq counter (1- counter))) ; @r{decrementer} @end group @end example @menu * Decrementing Example:: More pebbles on the beach. * Dec Example parts:: The parts of the function definition. * Dec Example altogether:: Putting the function definition together. @end menu @node Decrementing Example, Dec Example parts, Decrementing Loop, Decrementing Loop @unnumberedsubsubsec Example with decrementing counter To illustrate a loop with a decrementing counter, we will rewrite the @code{triangle} function so the counter decreases to zero. This is the reverse of the earlier version of the function. In this case, to find out how many pebbles are needed to make a triangle with 3 rows, add the number of pebbles in the third row, 3, to the number in the preceding row, 2, and then add the total of those two rows to the row that precedes them, which is 1. Likewise, to find the number of pebbles in a triangle with 7 rows, add the number of pebbles in the seventh row, 7, to the number in the preceding row, which is 6, and then add the total of those two rows to the row that precedes them, which is 5, and so on. As in the previous example, each addition only involves adding two numbers, the total of the rows already added up and the number of pebbles in the row that is being added to the total. This process of adding two numbers is repeated again and again until there are no more pebbles to add. We know how many pebbles to start with: the number of pebbles in the last row is equal to the number of rows. If the triangle has seven rows, the number of pebbles in the last row is 7. Likewise, we know how many pebbles are in the preceding row: it is one less than the number in the row. @node Dec Example parts, Dec Example altogether, Decrementing Example, Decrementing Loop @unnumberedsubsubsec The parts of the function definition We start with three variables: the total number of rows in the triangle; the number of pebbles in a row; and the total number of pebbles, which is what we want to calculate. These variables can be named @code{number-of-rows}, @code{number-of-pebbles-in-row}, and @code{total}, respectively. Both @code{total} and @code{number-of-pebbles-in-row} are used only inside the function and are declared with @code{let}. The initial value of @code{total} should, of course, be zero. However, the initial value of @code{number-of-pebbles-in-row} should be equal to the number of rows in the triangle, since the addition will start with the longest row. @need 1250 This means that the beginning of the @code{let} expression will look like this: @example @group (let ((total 0) (number-of-pebbles-in-row number-of-rows)) @var{body}@dots{}) @end group @end example The total number of pebbles can be found by repeatedly adding the number of pebbles in a row to the total already found, that is, by repeatedly evaluating the following expression: @example (setq total (+ total number-of-pebbles-in-row)) @end example @noindent After the @code{number-of-pebbles-in-row} is added to the @code{total}, the @code{number-of-pebbles-in-row} should be decremented by one, since the next time the loop repeats, the preceding row will be added to the total. The number of pebbles in a preceding row is one less than the number of pebbles in a row, so the built-in Emacs Lisp function @code{1-} can be used to compute the number of pebbles in the preceding row. This can be done with the following expression: @example @group (setq number-of-pebbles-in-row (1- number-of-pebbles-in-row)) @end group @end example Finally, we know that the @code{while} loop should stop making repeated additions when there are no pebbles in a row. So the test for the @code{while} loop is simply: @example (while (> number-of-pebbles-in-row 0) @end example @node Dec Example altogether, , Dec Example parts, Decrementing Loop @unnumberedsubsubsec Putting the function definition together Putting these expressions together, we have a function definition that looks like this: @example @group ;;; @r{First subtractive version.} (defun triangle (number-of-rows) "Add up the number of pebbles in a triangle." (let ((total 0) (number-of-pebbles-in-row number-of-rows)) (while (> number-of-pebbles-in-row 0) (setq total (+ total number-of-pebbles-in-row)) (setq number-of-pebbles-in-row (1- number-of-pebbles-in-row))) total)) @end group @end example As written, this function works. However, it turns out that one of the local variables, @code{number-of-pebbles-in-row}, is unneeded! @cindex Argument as local variable When the @code{triangle} function is evaluated, the symbol @code{number-of-rows} will be bound to a number, giving it an initial value. That number can be changed in the body of the function as if it were a local variable, without any fear that such a change will effect the value of the variable outside of the function. This is a very useful characteristic of Lisp; it means that the variable @code{number-of-rows} can be used anywhere in the function where @code{number-of-pebbles-in-row} is used. Here is a second version of the function written a bit more cleanly: @example @group (defun triangle (number) ; @r{Second version.} "Return sum of numbers 1 through NUMBER inclusive." (let ((total 0)) (while (> number 0) (setq total (+ total number)) (setq number (1- number))) total)) @end group @end example In brief, a properly written @code{while} loop will consist of three parts: @enumerate @item A test that will return false after the loop has repeated itself the correct number of times. @item An expression the evaluation of which will return the value desired after being repeatedly evaluated. @item An expression to change the value passed to the true-or-false-test so that the test returns false after the loop has repeated itself the right number of times. @end enumerate @node Recursion, Looping exercise, while, Loops & Recursion @comment node-name, next, previous, up @section Recursion @cindex Recursion A recursive function contains code that tells itself to evaluate itself. When the function evaluates itself, it again finds the code that tells itself to evaluate itself, so the function evaluates itself again @dots{} and again @dots{} A recursive function will keep telling itself to evaluate itself again forever unless it is also provided with a stop condition. A recursive function typically contains a conditional expression which has three parts: @enumerate @item A true-or-false-test that determines whether the function is called again, here called the @dfn{do-again-test}. @item The name of the function. @item An expression that causes the conditional expression to test false after the correct number of repetitions, here called the @dfn{next-step-expression}. @end enumerate Recursive functions can be much simpler than any other kind of function. Indeed, when people first start to use them, they often look so mysteriously simple as to be incomprehensible. Like riding a bicycle, reading a recursive function definition takes a certain knack which is hard at first but then seems simple. A template for a recursive function looks like this: @example @group (defun @var{name-of-recursive-function} (@var{argument-list}) "@var{documentation}@dots{}" @var{body}@dots{} (if @var{do-again-test} (@var{name-of-recursive-function} @var{next-step-expression}))) @end group @end example @noindent Each time the recursive function is evaluated, an argument is bound to the value of the next-step-expression; and that value is used in the do-again-test. The next-step-expression is designed so that the do-again-test returns false when the function should no longer be repeated. The do-again-test is sometimes called the @dfn{stop condition}, since it stops the repetitions when it tests false. @menu * Recursion with list:: Using a list as the test whether to recurse. * Recursive triangle function:: Replacing a @code{while} loop with recursion. * Recursion with cond:: Recursion example with a different conditional. @end menu @node Recursion with list, Recursive triangle function, Recursion, Recursion @comment node-name, next, previous, up @subsection Recursion with a List The example of a @code{while} loop that printed the elements of a list of numbers can be written recursively. Here is the code, including an expression to set the value of the variable @code{animals} to a list. This example must be copied to the @file{*scratch*} buffer and each expression must be evaluated there. Use @kbd{C-u C-x C-e} to evaluate the @code{(print-elements-recursively animals)} expression so that the results are printed in the buffer; otherwise the Lisp interpreter will try to squeeze the results into the one line of the echo area. Also, place your cursor immediately after the last closing parenthesis of the @code{print-elements-recursively} function, before the comment. Otherwise, the Lisp interpreter will try to evaluate the comment. @findex print-elements-recursively @example @group (setq animals '(giraffe gazelle lion tiger)) (defun print-elements-recursively (list) "Print each element of LIST on a line of its own. Uses recursion." (print (car list)) ; @r{body} (if list ; @r{do-again-test} (print-elements-recursively ; @r{recursive call} (cdr list)))) ; @r{next-step-expression} (print-elements-recursively animals) @end group @end example The @code{print-elements-recursively} function first prints the first element of the list, the @sc{car} of the list. Then, if the list is not empty, the function invokes itself, but gives itself as its argument, not the whole list, but the second and subsequent elements of the list, the @sc{cdr} of the list. When this evaluation occurs, the function prints the first element of the list it receives as its argument (which is the second element of the original list). Then, the @code{if} expression is evaluated and when true, the function calls itself with the @sc{cdr} of the list it is invoked with, which (the second time around) is the @sc{cdr} of the @sc{cdr} of the original list. Each time the function invokes itself, it invokes itself on a shorter version of the original list. Eventually, the function invokes itself on an empty list. The @code{print} function prints the empty list as @code{nil}. Next, the conditional expression tests the value of @code{list}. Since the value of @code{list} is @code{nil}, the @code{if} expression tests false so the then-part is not evaluated. The function as a whole then returns @code{nil}. Consequently, you see @code{nil} twice when you evaluate the function. When you evaluate @code{(print-elements-recursively animals)} in the @file{*scratch*} buffer, you see this result: @example @group giraffe gazelle lion tiger nil nil @end group @end example (The first @code{nil} is the value of the empty list that is printed; the second @code{nil} is the value returned by the whole function.) @node Recursive triangle function, Recursion with cond, Recursion with list, Recursion @comment node-name, next, previous, up @subsection Recursion in Place of a Counter @findex triangle-recursively The @code{triangle} function described in a previous section can also be written recursively. It looks like this: @example @group (defun triangle-recursively (number) "Return the sum of the numbers 1 through NUMBER inclusive. Uses recursion." (if (= number 1) ; @r{do-again-test} 1 ; @r{then-part} (+ number ; @r{else-part} (triangle-recursively ; @r{recursive call} (1- number))))) ; @r{next-step-expression} (triangle-recursively 7) @end group @end example @noindent You can install this function by evaluating it and then try it by evaluating @code{(triangle-recursively 7)}. (Remember to put your cursor immediately after the last parenthesis of the function definition, before the comment.) To understand how this function works, let's consider what happens in the various cases when the function is passed 1, 2, 3, or 4 as the value of its argument. First, what happens if the value of the argument is 1? The function has an @code{if} expression after the documentation string. It tests whether the value of @code{number} is equal to 1; if so, Emacs evaluates the then-part of the @code{if} expression, which returns the number 1 as the value of the function. (A triangle with one row has one pebble in it.) Suppose, however, that the value of the argument is 2. In this case, Emacs evaluates the else-part of the @code{if} expression. The else-part consists of an addition, the recursive call to @code{triangle-recursively} and a decrementing action; and it looks like this: @example (+ number (triangle-recursively (1- number))) @end example When Emacs evaluates this expression, the innermost expression is evaluated first; then the other parts in sequence. Here are the steps in detail: @table @i @item Step 1 @w{ } Evaluate the innermost expression. The innermost expression is @code{(1- number)} so Emacs decrements the value of @code{number} from 2 to 1. @item Step 2 @w{ } Evaluate the @code{triangle-recursively} function. It does not matter that this function is contained within itself. Emacs passes the result Step 1 as the argument used by this instance of the @code{triangle-recursively} function In this case, Emacs evaluates @code{triangle-recursively} with an argument of 1. This means that this evaluation of @code{triangle-recursively} returns 1. @item Step 3 @w{ } Evaluate the value of @code{number}. The variable @code{number} is the second element of the list that starts with @code{+}; its value is 2. @item Step 4 @w{ } Evaluate the @code{+} expression. The @code{+} expression receives two arguments, the first from the evaluation of @code{number} (Step 3) and the second from the evaluation of @code{triangle-recursively} (Step 2). The result of the addition is the sum of 2 plus 1, and the number 3 is returned, which is correct. A triangle with two rows has three pebbles in it. @end table @menu * Recursive Example arg of 3:: @end menu @node Recursive Example arg of 3, , Recursive triangle function, Recursive triangle function @unnumberedsubsubsec An argument of 3 Suppose that @code{triangle-recursively} is called with an argument of 3. @table @i @item Step 1 @w{ } Evaluate the do-again-test. The @code{if} expression is evaluated first. This is the do-again test and returns false, so the else-part of the @code{if} expression is evaluated. (Note that in this example, the do-again-test causes the function to call itself when it tests false, not when it tests true.) @item Step 2 @w{ } Evaluate the innermost expression of the else-part. The innermost expression of the else-part is evaluated, which decrements 3 to 2. This is the next-step-expression. @item Step 3 @w{ } Evaluate the @code{triangle-recursively} function. The number 2 is passed to the @code{triangle-recursively} function. We know what happens when Emacs evaluates @code{triangle-recursively} with an argument of 2. After going through the sequence of actions described earlier, it returns a value of 3. So that is what will happen here. @item Step 4 @w{ } Evaluate the addition. 3 will be passed as an argument to the addition and will be added to the number with which the function was called, which is 3. @end table @noindent The value returned by the function as a whole will be 6. Now that we know what will happen when @code{triangle-recursively} is called with an argument of 3, it is evident what will happen if it is called with an argument of 4: @quotation In the recursive call, the evaluation of @example (triangle-recursively (1- 4)) @end example @noindent will return the value of evaluating @example (triangle-recursively 3) @end example @noindent which is 6 and this value will be added to 4 by the addition in the third line. @end quotation @noindent The value returned by the function as a whole will be 10. Each time @code{triangle-recursively} is evaluated, it evaluates a version of itself with a smaller argument, until the argument is small enough so that it does not evaluate itself. @node Recursion with cond, , Recursive triangle function, Recursion @comment node-name, next, previous, up @subsection Recursion Example Using @code{cond} @findex cond The version of @code{triangle-recursively} described earlier is written with the @code{if} special form. It can also be written using another special form called @code{cond}. The name of the special form @code{cond} is an abbreviation of the word @samp{conditional}. Although the @code{cond} special form is not used as often in the Emacs Lisp sources as @code{if}, it is used often enough to justify explaining it. The template for a @code{cond} expression looks like this: @example @group (cond @var{body}@dots{}) @end group @end example @noindent where the @var{body} is a series of lists. Written out more fully, the template looks like this: @example @group (cond ((@var{first-true-or-false-test} @var{first-consequent}) (@var{second-true-or-false-test} @var{second-consequent}) (@var{third-true-or-false-test} @var{third-consequent}) @dots{}) @end group @end example When the Lisp interpreter evaluates the @code{cond} expression, it evaluates the first element (the @sc{car} or true-or-false-test) of the first expression in a series of expressions within the body of the @code{cond}. If the true-or-false-test returns @code{nil} the rest of that expression, the consequent, is skipped and the true-or-false-test of the next expression is evaluated. When an expression is found whose true-or-false-test returns a value that is not @code{nil}, the consequent of that expression is evaluated. The consequent can be one or more expressions. If the consequent consists of more than one expression, the expressions are evaluated in sequence and the value of the last one is returned. If the expression does not have a consequent, the value of the true-or-false-test is returned. If none of the true-or-false-tests test true, the @code{cond} expression returns @code{nil}. @need 1250 Written using @code{cond}, the @code{triangle} function looks like this: @example @group (defun triangle-using-cond (number) (cond ((<= number 0) 0) ((= number 1) 1) ((> number 1) (+ number (triangle-using-cond (1- number)))))) @end group @end example @noindent In this example, the @code{cond} returns 0 if the number is less than or equal to 0, it returns 1 if the number is 1 and it evaluates @code{(+ number (triangle-using-cond (1- number)))} if the number is greater than 1. @need 1500 @node Looping exercise, , Recursion, Loops & Recursion @section Looping Exercise @itemize @bullet @item Write a function similar to @code{triangle} in which each row has a value which is the square of the row number. Use a @code{while} loop. @item Write a function similar to @code{triangle} that multiplies instead of adds the values. @item Rewrite these two functions recursively. Rewrite these functions using @code{cond}. @c comma in printed title causes problem in Info cross reference @item Write a function for Texinfo mode that creates an index entry at the beginning of a paragraph for every @samp{@@dfn} within the paragraph. (In a Texinfo file, @samp{@@dfn} marks a definition. For more information, see @ifinfo @ref{Indicating, , Indicating Definitions, texinfo}.) @end ifinfo @iftex ``Indicating Definitions, Commands, etc.'' in @cite{Texinfo, The GNU Documentation Format}.) @end iftex @end itemize @node Regexp Search, Counting Words, Loops & Recursion, Top @comment node-name, next, previous, up @chapter Regular Expression Searches @cindex Searches, illustrating @cindex Regular expression searches @cindex Patterns, searching for @cindex Motion by sentence and paragraph @cindex Sentences, movement by @cindex Paragraphs, movement by Regular expression searches are used extensively in GNU Emacs. The two functions, @code{forward-sentence} and @code{forward-paragraph} illustrate these searches well. Regular expression searches are described in @ref{Regexp Search, , Regular Expression Search, emacs, The GNU Emacs Manual}, as well as in @ref{Regular Expressions, , , elisp, The GNU Emacs Lisp Reference Manual}. In writing this chapter, I am presuming that you have at least a mild acquaintance with them. The major point to remember is that regular expressions permit you to search for patterns as well as for literal strings of characters. For example, the code in @code{forward-sentence} searches for the pattern of possible characters that could mark the end of a sentence, and moves point to that spot. Before looking at the code for the @code{forward-sentence} function, it is worth considering what the pattern that marks the end of a sentence must be. The pattern is discussed in the next section; following that is a description of the regular expression search function, @code{re-forward-search}. The @code{forward-sentence} function is described in the section following. Finally, the @code{forward-paragraph} function is described in the last section of this chapter. @code{forward-paragraph} is a complex function that introduces several new features. @menu * sentence-end:: The regular expression for @code{sentence-end}. * re-search-forward:: Very similar to @code{search-forward}. * forward-sentence:: A straightforward example of regexp search. * forward-paragraph:: A somewhat complex example. * etags:: How to create your own @file{TAGS} table. * Regexp Review:: * re-search Exercises:: @end menu @node sentence-end, re-search-forward, Regexp Search, Regexp Search @comment node-name, next, previous, up @section The Regular Expression for @code{sentence-end} @findex sentence-end The symbol @code{sentence-end} is bound to the pattern that marks the end of a sentence. What should this regular expression be? Clearly, a sentence may be ended by a period, a question mark, or an exclamation mark. Indeed, only clauses that end with one of those three characters should be considered the end of a sentence. This means that the pattern should include the character set: @example [.?!] @end example However, we do not want @code{forward-sentence} merely to jump to a period, a question mark, or an exclamation mark, because such a character might be used in the middle of a sentence. A period, for example, is used after abbreviations. So other information is needed. According to convention, you type two spaces after every sentence, but only one space after a period, a question mark, or an exclamation mark in the body of a sentence. So a period, a question mark, or an exclamation mark followed by two spaces is a good indicator of an end of sentence. However, in a file, the two spaces may instead be a tab or the end of a line. This means that the regular expression should include these three items as alternatives. This group of alternatives will look like this: @example @group \\($\\| \\| \\) ^ ^^ TAB SPC @end group @end example @noindent Here, @samp{$} indicates the end of the line, and I have pointed out where the tab and two spaces are inserted in the expression. Both are inserted by putting the actual characters into the expression. Two backslashes, @samp{\\}, are required before the parentheses and vertical bars: the first backslash to quote the following backslash in Emacs; and the second to indicate that the following character, the parenthesis or the vertical bar, is special. Also, a sentence may be followed by one or more carriage returns, like this: @example @group [ ]* @end group @end example @noindent Like tabs and spaces, a carriage return is inserted into a regular expression by inserting it literally. The asterisk indicates that the @key{RET} is repeated zero or more times. But a sentence end does not consist only of a period, a question mark or an exclamation mark followed by appropriate space: a closing quotation mark or a closing brace of some kind may precede the space. Indeed more than one such mark or brace by precede the space. These require a expression that looks like this: @example []\"')@}]* @end example In this expression, the first @samp{]} is the first character in the expression; the second character is @samp{"}, which is preceded by a @samp{\} to tell Emacs the @samp{"} is @emph{not} special. The last three characters are @samp{'}, @samp{)}, and @samp{@}}. All this suggests what the regular expression pattern for matching the end of a sentence should be; and, indeed, if we evaluate @code{sentence-end} we find that it returns the following value: @example @group sentence-end @result{} "[.?!][]\"')@}]*\\($\\| \\| \\)[ ]*" @end group @end example @ignore @noindent (Note that here the @key{TAB}, two spaces, and @key{RET} are shown literally in the pattern.) This regular expression can be decyphered as follows: @table @code @item [.?!] The first part of the pattern is the three characters, a period, a question mark and an exclamation mark, within square brackets. The pattern must begin with one or other of these characters. @item []\"')@}]* The second part of the pattern is the group of closing braces and quotation marks, which can appear zero or more times. These may follow the period, question mark or exclamation mark. In a regular expression, the backslash, @samp{\}, followed by the double quotation mark, @samp{"}, indicates the class of string-quote characters. Usually, the double quotation mark is the only character in this class. The asterisk, @samp{*}, indicates that the items in the previous group (the group surrounded by square brackets, @samp{[]}) may be repeated zero or more times. @item \\($\\| \\| \\) The third part of the pattern is one or other of: either the end of a line, or two blank spaces, or a tab. The double back-slashes are used to prevent Emacs from reading the parentheses and vertical bars as part of the search pattern; the parentheses are used to mark the group and the vertical bars are used to indicated that the patterns to either side of them are alternatives. The dollar sign is used to indicate the end of a line and both the two spaces and the tab are each inserted as is to indicate what they are. @item [@key{RET}]* Finally, the last part of the pattern indicates that the end of the line or the whitespace following the period, question mark or exclamation mark may, but need not, be followed by one or more carriage returns. In the pattern, the carriage return is inserted as an actual carriage return between square brackets but here it is shown as @key{RET}. @end table @end ignore @node re-search-forward, forward-sentence, sentence-end, Regexp Search @comment node-name, next, previous, up @section The @code{re-search-forward} Function @findex re-search-forward The @code{re-search-forward} function is very like the @code{search-forward} function. (@xref{search-forward, , The @code{search-forward} Function}.) @code{re-search-forward} searches for a regular expression. If the search is successful, it leaves point immediately after the last character in the target. If the search is backwards, it leaves point just before the first character in the target. You may tell @code{re-search-forward} to return @code{t} for true. (Moving point is therefore a `side effect'.) Like @code{search-forward}, the @code{re-search-forward} function takes four arguments: @enumerate @item The first argument is the regular expression that the function searches for. The regular expression will be a string between quotations marks. @item The optional second argument limits how far the function will search; it is a bound, specified as a position in the buffer. @item The optional third argument specifies how the function responds to failure: @code{nil} as the third argument causes the function to signal an error (and print a message) when the search fails; any other value causes it to return @code{nil} if the search fails and @code{t} if the search succeeds. @item The optional fourth argument is the repeat count. A negative repeat count causes @code{re-search-forward} to search backwards. @end enumerate The template for @code{re-search-forward} looks like this: @example @group (re-search-forward "@var{regular-expression}" @var{limit-of-search} @var{what-to-do-if-search-fails} @var{repeat-count}) @end group @end example The second, third, and fourth arguments are optional. However, if you want to pass a value to either or both of the last two arguments, you must also pass a value to all the preceding arguments. Otherwise, the Lisp interpreter will mistake which argument you are passing the value to. In the @code{forward-sentence} function, the regular expression will be the value of the variable @code{sentence-end}, namely: @example @group "[.?!][]\"')@}]*\\($\\| \\| \\)[ ]*" @end group @end example @noindent The limit of the search will be the end of the paragraph (since a sentence cannot go beyond a paragraph). If the search fails, the function will return @code{nil}; and the repeat count will be provided by the argument to the @code{forward-sentence} function. @node forward-sentence, forward-paragraph, re-search-forward, Regexp Search @comment node-name, next, previous, up @section @code{forward-sentence} @findex forward-sentence The command to move the cursor forward a sentence is a straightforward illustration of how to use regular expression searches in Emacs Lisp. Indeed, the function looks longer and more complicated than it is; this is because the function is designed to go backwards as well as forwards; and, optionally, over more than one sentence. The function is usually bound to the key command @kbd{M-e}. @need 1250 Here is the code for @code{forward-sentence}: @smallexample @group (defun forward-sentence (&optional arg) "Move forward to next sentence-end. With argument, repeat. With negative argument, move backward repeatedly to sentence-beginning. Sentence ends are identified by the value of sentence-end treated as a regular expression. Also, every paragraph boundary terminates sentences as well." @end group @group (interactive "p") (or arg (setq arg 1)) (while (< arg 0) (let ((par-beg (save-excursion (start-of-paragraph-text) (point)))) (if (re-search-backward (concat sentence-end "[^ \t\n]") par-beg t) (goto-char (1- (match-end 0))) (goto-char par-beg))) (setq arg (1+ arg))) (while (> arg 0) (let ((par-end (save-excursion (end-of-paragraph-text) (point)))) (if (re-search-forward sentence-end par-end t) (skip-chars-backward " \t\n") (goto-char par-end))) (setq arg (1- arg)))) @end group @end smallexample The function looks long at first sight and it is best to look at its skeleton first, and then its muscle. The way to see the skeleton is to look at the expressions that start in the left-most columns: @example @group (defun forward-sentence (&optional arg) "@var{documentation}@dots{}" (interactive "p") (or arg (setq arg 1)) (while (< arg 0) @var{body-of-while-loop} (while (> arg 0) @var{body-of-while-loop} @end group @end example This looks much simpler! The function definition consists of documentation, an @code{interactive} expression, an @code{or} expression, and @code{while} loops. Let's look at each of these parts in turn. We note that the documentation is thorough and understandable. The function has an @code{interactive "p"} declaration. This means that the processed prefix argument, if any, is passed to the function as its argument. (This will be a number.) If the function is not passed an argument (it is optional) then the argument @code{arg} will be bound to 1. When @code{forward-sentence} is called non-interactively without an argument, @code{arg} is bound to @code{nil}. The @code{or} expression handles the prefix argument. What it does is either leave the value of @code{arg} as it is, but only if @code{arg} is bound to a value; or it sets the value of @code{arg} to 1, in the case when @code{arg} is bound to @code{nil}. @menu * fwd-sentence while loops:: Two @code{while} loops. * fwd-sentence re-search:: A regular expression search. @end menu @node fwd-sentence while loops, fwd-sentence re-search, forward-sentence, forward-sentence @unnumberedsubsubsec The @code{while} loops Two @code{while} loops follow the @code{or} expression. The first @code{while} has a true-or-false-test that tests true if the prefix argument for @code{forward-sentence} is a negative number. This is for going backwards. The body of this loop is similar to the body of the second @code{while} clause, but it is not exactly the same. We will skip this @code{while} loop and concentrate on the second @code{while} loop. @need 1500 The second @code{while} loop is for moving point forward. Its skeleton looks like this: @example @group (while (> arg 0) ; @r{true-or-false-test} (let @var{varlist} (if (@var{true-or-false-test}) @var{then-part} @var{else-part} (setq arg (1- arg)))) ; @code{while} @r{loop decrementer} @end group @end example The @code{while} loop is of the decrementing kind. (@xref{Decrementing Loop, , A Loop with a Decrementing Counter}.) It has a true-or-false-test that tests true so long as the counter (in this case, the variable @code{arg}) is greater than zero; and it has a decrementer that subtracts 1 from the value of the counter every time the loop repeats. If no prefix argument is given to @code{forward-sentence}, which is the most common way the command is used, this @code{while} loop will run once, since the value of @code{arg} will be 1. The body of the @code{while} loop consists of a @code{let} expression, which creates and binds a local variable, and has, as its body, an @code{if} expression. @need 1250 The body of the @code{while} loop looks like this: @example @group (let ((par-end (save-excursion (end-of-paragraph-text) (point)))) (if (re-search-forward sentence-end par-end t) (skip-chars-backward " \t\n") (goto-char par-end))) @end group @end example The @code{let} expression creates and binds the local variable @code{par-end}. As we shall see, this local variable is designed to provide a bound or limit to the regular expression search. If the search fails to find a proper sentence ending in the paragraph, it will stop on reaching the end of the paragraph. But first, let us examine how @code{par-end} is bound to the value of the end of the paragraph. What happens is that the @code{let} sets the value of @code{par-end} to the value returned when the Lisp interpreter evaluates the expression @example @group (save-excursion (end-of-paragraph-text) (point)) @end group @end example @noindent In this expression, @code{(end-of-paragraph-text)} moves point to the end of the paragraph, @code{(point)} returns the value of point, and then @code{save-excursion} restores point to its original position. Thus, the @code{let} binds @code{par-end} to the value returned by the @code{save-excursion} expression, which is the position of the end of the paragraph. (The @code{(end-of-paragraph-text)} function uses @code{forward-paragraph}, which we will discuss shortly.) Emacs next evaluates the body of the @code{let}, which is an @code{if} expression that looks like this: @example @group (if (re-search-forward sentence-end par-end t) ; @r{if-part} (skip-chars-backward " \t\n") ; @r{then-part} (goto-char par-end))) ; @r{else-part} @end group @end example The @code{if} tests whether its first argument is true and if so, evaluates its then-part; otherwise, the Emacs Lisp interpreter evaluates the else-part. The true-or-false-test of the @code{if} expression is the regular expression search. It may seem odd to have what looks like the `real work' of the @code{forward-sentence} function buried here, but this is a common way this kind of operation is carried out in Lisp. @node fwd-sentence re-search, , fwd-sentence while loops, forward-sentence @unnumberedsubsubsec The regular expression search The @code{re-search-forward} function searches for the end of the sentence, that is, for the pattern defined by the @code{sentence-end} regular expression. If the pattern is found---if the end of the sentence is found---then the @code{re-search-forward} function does two things: @enumerate @item The @code{re-search-forward} function carries out a side effect, which is to move point to the end of the occurrence found. @item The @code{re-search-forward} function returns a value of true. This is the value received by the @code{if}, and means that the search was successful. @end enumerate @noindent The side effect, the movement of point, is completed before the @code{if} function is handed the value returned by the successful conclusion of the search. When the @code{if} function receives the value of true from a successful call to @code{re-search-forward}, the @code{if} evaluates the then-part, which is the expression @code{(skip-chars-backward " \t\n")}. This expression moves backwards over any blank spaces, tabs or carriage returns until a printed character is found and then leaves point after the character. Since point has already been moved to the end of the pattern that marks the end of the sentence, this action leaves point right after the closing printed character of the sentence, which is usually a period. On the other hand, if the @code{re-search-forward} function fails to find a pattern marking the end of the sentence, the function returns false. The false then causes the @code{if} to evaluate its third argument, which is @code{(goto-char par-end)}: it moves point to the end of the paragraph. Regular expression searches are exceptionally useful and the pattern illustrated by @code{re-search-forward}, in which the search is the test of an @code{if} expression, is handy. You will see or write code incorporating this pattern often. @node forward-paragraph, etags, forward-sentence, Regexp Search @comment node-name, next, previous, up @section @code{forward-paragraph}: a Goldmine of Functions @findex forward-paragraph The @code{forward-paragraph} function moves point forward to the end of the paragraph. It is usually bound to @kbd{M-@}} and makes use of a number of functions that are important in themselves, including @code{let*}, @code{match-beginning}, and @code{looking-at}. The function definition for @code{forward-paragraph} is considerably longer than the function definition for @code{forward-sentence} because it works with a paragraph, each line of which may begin with a fill prefix. A fill prefix consists of a string of characters that are repeated at the beginning of each line. For example, in Lisp code, it is a convention to start each line of a paragraph-long comment with @samp{;;; }. In Text mode, four blank spaces make up another common fill prefix, creating an indented paragraph. (@xref{Fill Prefix, , , emacs, The GNU Emacs Manual}, for more information about fill prefixes.) The existence of a fill prefix means that in addition to being able to find the end of a paragraph whose lines begin on the left-most column, the @code{forward-paragraph} function must be able to find the end of a paragraph when all or many of the lines in the buffer begin with the fill prefix. Moreover, it is sometimes practical to ignore a fill prefix that exists, especially when blank lines separate paragraphs. This is an added complication. Rather than print all of the @code{forward-paragraph} function, we will only print parts of it. Read without preparation, the function can be daunting! In outline, the function looks like this: @example @group (defun forward-paragraph (&optional arg) "@var{documentation}@dots{}" (interactive "p") (or arg (setq arg 1)) (let* @var{varlist} (while (< arg 0) ; @r{backward-moving-code} @dots{} (setq arg (1+ arg))) (while (> arg 0) ; @r{forward-moving-code} @dots{} (setq arg (1- arg))))) @end group @end example The first parts of the function are routine: the function's argument list consists of one optional argument. Documentation follows. The lower case @samp{p} in the @code{interactive} declaration means that the processed prefix argument, if any, is passed to the function. This will be a number, and is the repeat count of how many paragraphs point will move. The @code{or} expression in the next line handles the common case when no argument is passed the function, which occurs if the function is called from other code rather than interactively. This case was described earlier. (@xref{forward-sentence, The @code{forward-sentence} function}.) Now we reach the end of the familiar part of this function. @menu * fwd-para let:: The @code{let*} expression. * fwd-para while:: The forward motion @code{while} loop. * fwd-para between paragraphs:: Movement between paragraphs. * fwd-para within paragraph:: Movement within paragraphs. * fwd-para no fill prefix:: When there is no fill prefix. * fwd-para with fill prefix:: When there is a fill prefix. * fwd-para summary:: Summary of @code{forward-paragraph} code. @end menu @node fwd-para let, fwd-para while, forward-paragraph, forward-paragraph @unnumberedsubsubsec The @code{let*} expression The next line of the @code{forward-paragraph} function begins a @code{let*} expression. This is a different kind of expression than we have seen so far. The symbol is @code{let*} not @code{let}. The @code{let*} special form is like @code{let} except that Emacs sets each variable in sequence, one after another, and variables in the latter part of the varlist can make use of the values to which Emacs set variables in the earlier part of the varlist. In the @code{let*} expression in this function, Emacs binds two variables: @code{fill-prefix-regexp} and @code{paragraph-separate}. The value to which @code{paragraph-separate} is bound depends on the value of @code{fill-prefix-regexp}. Let's look at each in turn. The symbol @code{fill-prefix-regexp} is set to the value returned by evaluating the following list: @example @group (and fill-prefix (not (equal fill-prefix "")) (not paragraph-ignore-fill-prefix) (regexp-quote fill-prefix)) @end group @end example @noindent This is an expression whose first element is the function @code{and}. The @code{and} function evaluates each of its arguments until one of the arguments returns a value of @code{nil}, in which case the @code{and} expression returns @code{nil}; however, if none of the arguments returns a value of @code{nil}, the value resulting from evaluating the last argument is returned. (Since such a value is not @code{nil}, it is considered true in Lisp.) In other words, an @code{and} expression returns a true value only if all its arguments are true. @findex and In this case, the variable @code{fill-prefix-regexp} is bound to a non-@code{nil} value only if the following four expressions produce a true (i.e., a non-@code{nil}) value when they are evaluated; otherwise, @code{fill-prefix-regexp} is bound to @code{nil}. @table @code @item fill-prefix When this variable is evaluated, the value of the fill prefix, if any, is returned. If there is no fill prefix, this variable returns @code{nil}. @item (not (equal fill-prefix "") This expression checks whether an existing fill prefix is an empty string, that is, a string with no characters in it. An empty string is not a useful fill prefix. @item (not paragraph-ignore-fill-prefix) This expression returns @code{nil} if the variable @code{paragraph-ignore-fill-prefix} has been turned on by being set to a true value such as @code{t}. @item (regexp-quote fill-prefix) This is the last argument to the @code{and} function. If all the arguments to the @code{and} are true, the value resulting from evaluating this expression will be returned by the @code{and} expression and bound to the variable @code{fill-prefix-regexp}, @end table @findex regexp-quote @noindent The result of evaluating this @code{and} expression successfully is that @code{fill-prefix-regexp} will be bound to the value of @code{fill-prefix} as modified by the @code{regexp-quote} function. What @code{regexp-quote} does is read a string and return a regular expression that will exactly match the string and match nothing else. This means that @code{fill-prefix-regexp} will be set to a value that will exactly match the fill prefix if the fill prefix exists. Otherwise, the variable will be set to @code{nil}. The second local variable in the @code{let*} expression is @code{paragraph-separate}. It is bound to the value returned by evaluating the expression: @example @group (if fill-prefix-regexp (concat paragraph-separate "\\|^" fill-prefix-regexp "[ \t]*$") paragraph-separate))) @end group @end example This expression shows why @code{let*} rather than @code{let} was used. The true-or-false-test for the @code{if} depends on whether the variable @code{fill-prefix-regexp} evaluates to @code{nil} or some other value. If @code{fill-prefix-regexp} does not have a value, Emacs evaluates the else-part of the @code{if} expression and binds @code{paragraph-separate} to its local value. (@code{paragraph-separate} is a regular expression that matches what separates paragraphs.) But if @code{fill-prefix-regexp} does have a value, Emacs evaluates the then-part of the @code{if} expression and binds @code{paragraph-separate} to a regular expression that includes the @code{fill-prefix-regexp} as part of the pattern. Specifically, @code{paragraph-separate} is set to the original value of the paragraph separate regular expression concatenated with an alternative expression that consists of the @code{fill-prefix-regexp} followed by a blank line. The @samp{^} indicates that the @code{fill-prefix-regexp} must begin a line, and the optional whitespace to the end of the line is defined by @w{@code{"[ \t]*$"}}.) The @samp{\\|} defines this portion of the regexp as an alternative to @code{paragraph-separate}. Now we get into the body of the @code{let*}. The first part of the body of the @code{let*} deals with the case when the function is given a negative argument and is therefore moving backwards. We will skip this section. @node fwd-para while, fwd-para between paragraphs, fwd-para let, forward-paragraph @unnumberedsubsubsec The forward motion @code{while} loop The second part of the body of the @code{let*} deals with forward motion. It is a @code{while} loop that repeats itself so long as the value of @code{arg} is greater than zero. In the most common use of the function, the value of the argument is 1, so the body of the @code{while} loop is evaluated exactly once, and the cursor moves forward one paragraph. This part handles three situations: when point is between paragraphs, when point is within a paragraph and there is a fill prefix, and when point is within a paragraph and there is no fill prefix. The @code{while} loop looks like this: @example @group (while (> arg 0) (beginning-of-line) ;; @r{between paragraphs} (while (prog1 (and (not (eobp)) (looking-at paragraph-separate)) (forward-line 1))) @end group @group ;; @r{within paragraphs, with a fill prefix} (if fill-prefix-regexp ;; @r{There is a fill prefix; it overrides paragraph-start.} (while (and (not (eobp)) (not (looking-at paragraph-separate)) (looking-at fill-prefix-regexp)) (forward-line 1)) @end group @group ;; @r{within paragraphs, no fill prefix} (if (re-search-forward paragraph-start nil t) (goto-char (match-beginning 0)) (goto-char (point-max)))) (setq arg (1- arg))) @end group @end example We can see immediately that this is a decrementing counter @code{while} loop, using the expression @code{(setq (1- arg))} as the decrementer. The body of the loop consists of three expressions: @example @group ;; @r{between paragraphs} (beginning-of-line) (while @var{body-of-while}) @end group @group ;; @r{within paragraphs, with fill prefix} (if @var{true-or-false-test} @var{then-part} @end group @group ;; @r{within paragraphs, no fill prefix} @var{else-part} @end group @end example @noindent When the Emacs Lisp interpreter evaluates the body of the @code{while} loop, the first thing it does is evaluate the @code{(beginning-of-line)} expression and move point to the beginning of the line. Then there is an inner @code{while} loop. This @code{while} loop is designed to move the cursor out of the blank space between paragraphs, if it should happen to be there. Finally there is an @code{if} expression that actually moves point to the end of the paragraph. @node fwd-para between paragraphs, fwd-para within paragraph, fwd-para while, forward-paragraph @unnumberedsubsubsec Between paragraphs First, let us look at the inner @code{while} loop. This loop handles the case when point is between paragraphs; it uses three functions that are new to us: @code{prog1}, @code{eobp} and @code{looking-at}. @findex prog1 @findex eobp @findex looking-at @itemize @bullet @item @code{prog1} is similar to the @code{progn} function, except that @code{prog1} evaluates its arguments in sequence and then returns the value of its first argument as the value of the whole expression. (@code{progn} returns the value of its last argument as the value of the expression.) The second and subsequent arguments to @code{prog1} are evaluated only for their side effects. @item @code{eobp} is an abbreviation of @samp{End Of Buffer P} and is a function that returns true if point is at the end of the buffer. @item @code{looking-at} is a function that returns true if the text following point matches the regular expression passed @code{looking-at} as its argument. @end itemize The @code{while} loop we are studying looks like this: @example @group (while (prog1 (and (not (eobp)) (looking-at paragraph-separate)) (forward-line 1))) @end group @end example @noindent This is a @code{while} loop with no body! The true-or-false-test of the loop is the expression: @example @group (prog1 (and (not (eobp)) (looking-at paragraph-separate)) (forward-line 1))) @end group @end example @noindent The first argument to the @code{prog1} is the @code{and} expression. It has within in it a test of whether point is at the end of the buffer and also a test of whether the pattern following point matches the regular expression for separating paragraphs. If the cursor is not at the end of the buffer and if the characters following the cursor mark the separation between two paragraphs, then the @code{and} expression is true. After evaluating the @code{and} expression, the Lisp interpreter evaluates the second argument to @code{prog1}, which is @code{forward-line}. This moves point forward one line. The value returned by the @code{prog1} however, is the value of its first argument, so the @code{while} loop continues so long as point is not at the end of the buffer and is between paragraphs. When, finally, point is moved to a paragraph, the @code{and} expression tests false. Note however, that the @code{forward-line} command is carried out anyhow. This means that when point is moved from between paragraphs to a paragraph, it is left at the beginning of the second line of the paragraph. @node fwd-para within paragraph, fwd-para no fill prefix, fwd-para between paragraphs, forward-paragraph @unnumberedsubsubsec Within paragraphs The next expression in the outer @code{while} loop is an @code{if} expression. The Lisp interpreter evaluates the then-part of the @code{if} when the @code{fill-prefix-regexp} variable has a value other than @code{nil}, and it evaluates the else-part when the value of @code{if fill-prefix-regexp} is @code{nil}, that is, when there is no fill prefix. @node fwd-para no fill prefix, fwd-para with fill prefix, fwd-para within paragraph, forward-paragraph @unnumberedsubsubsec No fill prefix It is simplest to look at the code for the case when there is no fill prefix first. This code consists of yet another inner @code{if} expression, and reads as follows: @example @group (if (re-search-forward paragraph-start nil t) (goto-char (match-beginning 0)) (goto-char (point-max))) @end group @end example @noindent This expression actually does the work that most people think of as the primary purpose of the @code{forward-paragraph} command: it causes a regular expression search to occur that searches forward to the start of the next paragraph and if it is found, moves point there; but if the start of another paragraph if not found, it moves point to the end of the accessible region of the buffer. The only unfamiliar part of this is the use of @code{match-beginning}. This is another function that is new to us. The @code{match-beginning} function returns a number specifying the location of the start of the text that was matched by the last regular expression search. The @code{match-beginning} function is used here because of a characteristic of a forward search: a successful forward search, regardless of whether it is a plain search or a regular expression search, will move point to the end of the text that is found. In this case, a successful search will move point to the end of the pattern for @code{paragraph-start}, which will be the beginning of the next paragraph rather than the end of the current one. However, we want to put point at the end of the current paragraph, not at the beginning of the next one. The two positions may be different, because there may be several blank lines between paragraphs. @findex match-beginning When given an argument of 0, @code{match-beginning} returns the position that is the start of the text that the most recent regular expression search matched. In this case, the most recent regular expression search is the one looking for @code{paragraph-start}, so @code{match-beginning} returns the beginning position of the pattern, rather than the end of the pattern. The beginning position is the end of the paragraph. (Incidentally, when passed a positive number as an argument, the @code{match-beginning} function will place point at that parenthesized expression in the last regular expression. It is a useful function.) @node fwd-para with fill prefix, fwd-para summary, fwd-para no fill prefix, forward-paragraph @unnumberedsubsubsec With a fill prefix The inner @code{if} expression just discussed is the else-part of an enclosing @code{if} expression which tests whether there is a fill prefix. If there is a fill prefix, the then-part of this @code{if} is evaluated. It looks like this: @example @group (while (and (not (eobp)) (not (looking-at paragraph-separate)) (looking-at fill-prefix-regexp)) (forward-line 1)) @end group @end example @noindent What this expression does is move point forward line by line so long as three conditions are true: @enumerate @item Point is not at the end of the buffer. @item The text following point does not separate paragraphs. @item The pattern following point is the fill prefix regular expression. @end enumerate The last condition may be puzzling, until you remember that point was moved to the beginning of the line early in the @code{forward-paragraph} function. This means that if the text has a fill prefix, the @code{looking-at} function will see it. @node fwd-para summary, , fwd-para with fill prefix, forward-paragraph @unnumberedsubsubsec Summary In summary, when moving forward, the @code{forward-paragraph} function does the following: @itemize @bullet @item Move point to the beginning of the line. @item Skip over lines between paragraphs. @item Check whether there is a fill prefix, and if there is: @itemize --- @item Go forward line by line so long as the line is not a paragraph separating line. @end itemize @item But if there is no fill prefix, @itemize --- @item Search for the next paragraph start pattern. @item Go to the beginning of the paragraph start pattern, which will be the end of the previous paragraph. @item Or else go to the end of the accessible portion of the buffer. @end itemize @end itemize For review, here is the code we have just been discussing, formatted for clarity: @example @group (interactive "p") (or arg (setq arg 1)) (let* ( (fill-prefix-regexp (and fill-prefix (not (equal fill-prefix "")) (not paragraph-ignore-fill-prefix) (regexp-quote fill-prefix))) @end group @group (paragraph-separate (if fill-prefix-regexp (concat paragraph-separate "\\|^" fill-prefix-regexp "[ \t]*$") paragraph-separate))) @var{backward-moving-code (omitted)} @dots{} @end group @group (while (> arg 0) ; @r{forward-moving-code} (beginning-of-line) (while (prog1 (and (not (eobp)) (looking-at paragraph-separate)) (forward-line 1))) @end group @group (if fill-prefix-regexp (while (and (not (eobp)) ; @r{then-part} (not (looking-at paragraph-separate)) (looking-at fill-prefix-regexp)) (forward-line 1)) @end group @group ; @r{else-part: the inner-if} (if (re-search-forward paragraph-start nil t) (goto-char (match-beginning 0)) (goto-char (point-max)))) (setq arg (1- arg))))) ; @r{decrementer} @end group @end example The full definition for the @code{forward-paragraph} function not only includes this code for going forwards, but also code for going backwards. If you are reading this inside of GNU Emacs and you want to see the whole function, you can type @kbd{M-.} (@code{find-tag}) and the name of the function when prompted for it. If the @code{find-tag} function first asks you for the name of a @file{TAGS} table, give it the name of the @file{TAGS} file in your @file{emacs/src} directory, which will have a pathname such as @file{/usr/local/lib/emacs/19.23/src/TAGS}. (The exact path to the @file{emacs/src} directory depends on how your copy of Emacs was installed. If you don't know the path, you can sometimes find out by typing @kbd{C-h i} to enter Info and then typing @kbd{C-x C-f} to see the path to the @file{emacs/info} directory. The path to the @file{TAGS} file is often the corresponding @file{emacs/src} path; sometimes, however, Info files are stored elsewhere.) You can also create your own @file{TAGS} file for directories that lack one. @ifinfo @xref{etags, , Create Your Own @file{TAGS} File}. @end ifinfo @node etags, Regexp Review, forward-paragraph, Regexp Search @section Create Your Own @file{TAGS} File @findex etags @cindex @file{TAGS} file, create own You can create your own @file{TAGS} file to help you jump to sources. For example, if you have a large number of files in your @file{~/emacs} directory, as I do---I have 137 @file{.el} files in it, of which I load 17--- you will find it easier to jump to specific functions if you create a @file{TAGS} file for that directory than if you search for the function name with @code{grep} or some other tool. You can create a @file{TAGS} file by calling the @code{etags} program that comes as a part of the Emacs distribution. Usually, @code{etags} is compiled and installed when Emacs is built. (@code{etags} is not an Emacs Lisp function or a part of Emacs; it is a C program.) To create a @file{TAGS} file, first switch to the directory in which you want to create the file. In Emacs you can do this with the @kbd{M-x cd} command, or by visiting a file in the directory, or by listing the directory with @kbd{C-x d} (@code{dired}). Then type @example M-! etags *.el @end example @noindent to create a @file{TAGS} file. The @code{etags} program takes all the usual shell `wildcards'. For example, if you have two directories for which you want a single @file{TAGS file}, type the command like this, where @file{../elisp/} is the second directory: @example M-! etags *.el ../elisp/*.el @end example @need 1250 Type @example M-! etags --help @end example @noindent to see a list of the options accepted by @code{etags}. The @code{etags} program handles Emacs Lisp, Common Lisp, Scheme, C, Fortran, Pascal, LaTeX, and most assemblers. The program has no switches for specifying the language; it recognizes the language in an input file according to its file name and contents. Also, @file{etags} is very helpful when you are writing code yourself and want to refer back to functions you have already written. Just run @code{etags} again at intervals as you write new functions, so they become part of the @file{TAGS} file. @node Regexp Review, re-search Exercises, etags, Regexp Search @comment node-name, next, previous, up @section Review Here is a brief summary of some recently introduced functions. @table @code @item while Repeatedly evaluate the body of the expression so long as the first element of the body tests true. Then return @code{nil}. (The expression is evaluated only for its side effects.) @need 1250 For example: @example @group (let ((foo 2)) (while (> foo 0) (insert (format "foo is %d.\n" foo)) (setq foo (1- foo)))) @result{} foo is 2. foo is 1. nil @end group @end example @noindent (The @code{insert} function inserts its arguments at point; the @code{format} function returns a string formatted from its arguments the way @code{message} formats its arguments; @code{\n} produces a new line.) @item re-search-forward Search for a pattern, and if the pattern is found, move point to rest just after it. @noindent Takes four arguments, like @code{search-forward}: @enumerate @item A regular expression that specifies the pattern to search for. @item Optionally, the limit of the search. @item Optionally, what to do if the search fails, return @code{nil} or an error message. @item Optionally, how many times to repeat the search; if negative, the search goes backwards. @end enumerate @item let* Bind some variables locally to particular values, and then evaluate the remaining arguments, returning the value of the last one. While binding the local variables, use the local values of variables bound earlier, if any. @need 1250 For example: @example @group (let* ((foo 7) (bar (* 3 foo))) (message "`bar' is %d." bar)) @result{} `bar' is 21. @end group @end example @item match-beginning Return the position of the start of the text found by the last regular expression search. @item looking-at Return @code{t} for true if the text after point matches the argument, which should be a regular expression. @item eobp Return @code{t} for true if point is at the end of the accessible part of a buffer. The end of the accessible part is the end of the buffer if the buffer is not narrowed; it is the end of the narrowed part if the buffer is narrowed. @item prog1 Evaluate each argument in sequence and then return the value of the @emph{first}. @need 1250 For example: @example @group (prog1 1 2 3 4) @result{} 1 @end group @end example @end table @need 1500 @node re-search Exercises, , Regexp Review, Regexp Search @section Exercises with @code{re-search-forward} @itemize @bullet @item Write a function to search for a regular expression that matches two or more blank lines in sequence. @item Write a function to search for duplicated words, such as `the the'. @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs Manual}, for information on how to write a regexp (a regular expression) to match a string that is composed of two identical halves. You can devise several regexps; some are better than others. The function I use is described in an appendix, along with several regexps. @xref{the-the, , @code{the-the} Duplicated Words Function}. @end itemize @node Counting Words, Words in a defun, Regexp Search, Top @chapter Counting: Repetition and Regexps @cindex Repetition for word counting @cindex Regular expressions for word counting Repetition and regular expression searches are powerful tools that you often use when you write code in Emacs Lisp. This chapter illustrates the use of regular expression searches through the construction of word count commands using @code{while} loops and recursion. @menu * Why Count Words:: Emacs lacks a word count command. * count-words-region:: Use a regexp, but find a problem. * recursive-count-words:: Start with case of no words in region. * Counting Exercise:: @end menu @node Why Count Words, count-words-region, Counting Words, Counting Words @ifinfo @heading Counting words @end ifinfo The standard Emacs distribution contains a function for counting the number of lines within a region. However, there is no corresponding function for counting words. Certain types of writing ask you to count words. Thus, if you write an essay, you may be limited to 800 words; if you write a novel, you may discipline yourself to write 1000 words a day. It seems odd to me that Emacs lacks a word count command. Perhaps people use Emacs mostly for code or types of documentation that do not require word counts; or perhaps they restrict themselves to the operating system word count command, @code{wc}. Alternatively, people may follow the publishers' convention and compute a word count by dividing the number of characters in a document by five. In any event, here are commands to count words. @node count-words-region, recursive-count-words, Why Count Words, Counting Words @comment node-name, next, previous, up @section The @code{count-words-region} Function @findex count-words-region A word count command could count words in a line, paragraph, region, or buffer. What should the command cover? You could design the command to count the number of words in a complete buffer. However, the Emacs tradition encourages flexibility---you may want to count words in just a section, rather than all of a buffer. So it makes more sense to design the command to count the number of words in a region. Once you have a @code{count-words-region} command, you can, if you wish, count words in a whole buffer by marking it with @kbd{C-x h} (@code{mark-whole-buffer}). Clearly, counting words is a repetitive act: starting from the beginning of the region, you count the first word, then the second word, then the third word, and so on, until you reach the end of the region. This means that word counting is ideally suited to recursion or to a @code{while} loop. First, we will implement the word count command with a @code{while} loop, then with recursion. The command will, of course, be interactive. The template for an interactive function definition is, as always: @example @group (defun @var{name-of-function} (@var{argument-list}) "@var{documentation}@dots{}" (@var{interactive-expression}@dots{}) @var{body}@dots{}) @end group @end example What we need to do is fill in the slots. The name of the function should be self-explanatory and similar to the existing @code{count-lines-region} name. This makes the name easier to remember. @code{count-words-region} is a good choice. The function counts words within a region. This means that the argument list must contain symbols that are bound to the two positions, the beginning and end of the region. These two positions can be called @samp{beginning} and @samp{end} respectively. The first line of the documentation should be a single sentence, since that is all that is printed as documentation by a command such as @code{apropos}. The interactive expression will be of the form @samp{(interactive "r")}, since that will cause Emacs to pass the beginning and end of the region to the function's argument list. All this is routine. The body of the function needs to be written so as to do three tasks: first to set up conditions under which the @code{while} loop can count words, second to run the @code{while} loop, and, third, to send a message to the user. When a user calls @code{count-words-region}, point may be at the beginning or the end of the region. However, the counting process must start at the beginning of the region. These means we will want to put point there if it is not already there. Executing @code{(goto-char beginning)} ensures this. Of course, we will want to return point to its expected position when the function finishes its work. For this reason, the body must be enclosed in a @code{save-excursion} expression. The central part of the body of the function consists of a @code{while} loop in which one expression jumps point forward word by word, and another expression counts those jumps. The true-or-false-test of the @code{while} loop should test true so long as point should jump forward, and false when point is at the end of the region. We could use @code{(forward-word 1)} as the expression for moving point forward word by word, but it is easier to see what Emacs identifies as a `word' if we use a regular expression search. A regular expression search that finds the pattern for which it is searching leaves point after the last character matched. This means that a succession of successful word searches will move point forward word by word. As a practical matter, we want the regular expression search to jump over whitespace and punctuation between words as well as over the words themselves. A regexp that refuses to jump over interword whitespace would never jump more than one word! This means that the regexp should include the whitespace and punctuation that follows a word, if any, as well as the word itself. (A word may end a buffer and not have any following whitespace or punctuation, so that part of the regexp must be optional.) Thus, what we want for the regexp is a pattern defining one or more word constituent characters followed, optionally, by one or more characters that are not word constituents. The regular expression for this is: @example \w+\W* @end example @noindent The buffer's syntax table determines which characters are and are not word constituents. (@xref{Syntax, , What Constitutes a Word or Symbol?}, for more about syntax. Also, see @ref{Syntax, Syntax, The Syntax Table, emacs, The GNU Emacs Manual}, and, @ref{Syntax Tables, , Syntax Tables, elisp, The GNU Emacs Lisp Reference Manual}.) The search expression looks like this: @example (re-search-forward "\\w+\\W*") @end example @noindent (Note that paired backslashes precede the @samp{w} and @samp{W}. A single backslash has special meaning to the Emacs Lisp interpreter. It indicates that the following character is interpreted differently than usual. For example, the two characters, @samp{\n}, stand for @samp{newline}, rather than for a backslash followed by @samp{n}. Two backslashes in a row stand for an ordinary, `unspecial' backslash.) We need a counter to count how many words there are; this variable must first be set to 0 and then incremented each time Emacs goes around the @code{while} loop. The incrementing expression is simply: @example (setq count (1+ count)) @end example Finally, we want to tell the user how many words there are in the region. The @code{message} function is intended for presenting this kind of information to the user. The message has to be phrased so that it reads properly regardless of how many words there are in the region: we don't want to say that ``there are 1 words in the region''. The conflict between singular and plural is ungrammmatical. We can solve this problem by using a conditional expression that evaluates different messages depending on the number of words in the region. There are three possibilities: no words in the region, one word in the region, and more than one word. This means that the @code{cond} special form is appropriate. @need 1500 All this leads to the following function definition: @example @group ;;; @r{First version; has bugs!} (defun count-words-region (beginning end) "Print number of words in the region. Words are defined as at least one word-constituent character followed by at least one character that is not a word-constituent. The buffer's syntax table determines which characters these are." (interactive "r") (message "Counting words in region ... ") @end group @group ;;; @r{1. Set up appropriate conditions.} (save-excursion (goto-char beginning) (let ((count 0)) @end group @group ;;; @r{2. Run the} while @r{loop.} (while (< (point) end) (re-search-forward "\\w+\\W*") (setq count (1+ count))) @end group @group ;;; @r{3. Send a message to the user.} (cond ((zerop count) (message "The region does NOT have any words.")) ((= 1 count) (message "The region has 1 word.")) (t (message "The region has %d words." count)))))) @end group @end example @noindent As written, the function works, but not in all circumstances. @menu * Whitespace Bug:: The Whitespace Bug in @code{count-words-region} @end menu @node Whitespace Bug, , count-words-region, count-words-region @comment node-name, next, previous, up @subsection The Whitespace Bug in @code{count-words-region} The @code{count-words-region} command described in the preceding section has two bugs, or rather, one bug with two manifestations. First, if you mark a region containing only whitespace in the middle of some text, the @code{count-words-region} command tells you that the region contains one word! Second, if you mark a region containing only whitespace at the end of the buffer or the accessible portion of a narrowed buffer, the command displays an error message that looks like this: @example Search failed: "\\w+\\W*" @end example If you are reading this in Info in GNU Emacs, you can test for these bugs yourself. First, evaluate the function in the usual manner to install it. @ifinfo Here is a copy of the definition. Place your cursor after the closing parenthesis and type @kbd{C-x C-e} to install it. @example @group ;; @r{First version; has bugs!} (defun count-words-region (beginning end) "Print number of words in the region. Words are defined as at least one word-constituent character followed by at least one character that is not a word-constituent. The buffer's syntax table determines which characters these are." @end group @group (interactive "r") (message "Counting words in region ... ") @end group @group ;;; @r{1. Set up appropriate conditions.} (save-excursion (goto-char beginning) (let ((count 0)) @end group @group ;;; @r{2. Run the} while @r{loop.} (while (< (point) end) (re-search-forward "\\w+\\W*") (setq count (1+ count))) @end group @group ;;; @r{3. Send a message to the user.} (cond ((zerop count) (message "The region does NOT have any words.")) ((= 1 count) (message "The region has 1 word.")) (t (message "The region has %d words." count)))))) @end group @end example @end ifinfo If you wish, you can also install this keybinding by evaluating it, too: @example (global-set-key "\C-c=" 'count-words-region) @end example To conduct the first test, set mark and point to the beginning and end of the following line and then type @kbd{C-c =} (or @kbd{M-x count-words-region} if you have not bound @kbd{C-c =}): @example one two three @end example @noindent Emacs will tell you, correctly, that the region has three words. Repeat the test, but place mark at the beginning of the line and place point just @emph{before} the word @samp{one}. Again type the command @kbd{C-c =} (or @kbd{M-x count-words-region}). Emacs should tell you that the region has no words, since it is composed only of the whitespace at the beginning of the line. But instead Emacs tells you that the region has one word! For the third test, copy the sample line to the end of the @file{*scratch*} buffer and then type several spaces at the end of the line. Place mark right after the word @samp{three} and point at the end of line. (The end of the line will be the end of the buffer.) Type @kbd{C-c =} (or @kbd{M-x count-words-region}) as you did before. Again, Emacs should tell you that the region has no words, since it is composed only of the whitespace at the end of the line. Instead, Emacs displays an error message saying @samp{Search failed}. The two bugs stem from the same problem. Consider the first manifestation of the bug, in which the command tells you that the whitespace at the beginning of the line contains one word. What happens is this: The @code{M-x count-words-region} command moves point to the beginning of the region. The @code{while} tests whether the value of point is smaller than the value of @code{end}, which it is. Consequently, the regular expression search looks for and finds the first word. It leaves point after the word. @code{count} is set to one. The @code{while} loop repeats; but this time the value of point is larger than the value of @code{end}, the loop is exited; and the function displays a message saying the number of words in the region is one. In brief, the regular expression search looks for and finds the word even though it is outside the marked region. In the second manifestation of the bug, the region is whitespace at the end of the buffer. Emacs says @samp{Search failed}. What happens is that the true-or-false-test in the @code{while} loop tests true, so the search expression is executed. But since there are no more words in the buffer, the search fails. In both manifestations of the bug, the search extends or attempts to extend outside of the region. The solution is to limit the search to the region---this is a fairly simple action, but as you may have come to expect, it is not quite as simple as you might think. As we have seen, the @code{re-search-forward} function takes a search pattern as its first argument. But in addition to this first, mandatory argument, it accepts three optional arguments. The optional second argument bounds the search. The optional third argument, if @code{t}, causes the function to return @code{nil} rather than signal an error if the search fails. The optional fourth argument is a repeat count. (In Emacs, you can get a function's documentation by typing @kbd{C-h f}, the name of the function, and then @key{RET}.) In the @code{count-words-region} definition, the value of the end of the region is held by the variable @code{end} which is passed as an argument to the function. Thus, we can add @code{end} as an argument to the regular expression search expression: @example (re-search-forward "\\w+\\W*" end) @end example However, if you make only this change to the @code{count-words-region} definition and then test the new version of the definition on a stretch of whitespace, you will receive an error message saying @samp{Search failed}. What happens is this: the search is limited to the region, and fails as you expect because there are no word-constituent characters in the region. Since it fails, we receive an error message. But we do not want to receive an error message in this case; we want to receive the message that "The region does NOT have any words." The solution to this problem is to provide @code{re-search-forward} with a third argument of @code{t}, which causes the function to return @code{nil} rather than signal an error if the search fails. However, if you make this change and try it, you will see the message ``Counting words in region ... '' and @dots{} you will keep on seeing that message @dots{}, until you type @kbd{C-g} (@code{keyboard-quit}). Here is what happens: the search is limited to the region, as before, and it fails because there are no word-constituent characters in the region, as expected. Consequently, the @code{re-search-forward} expression returns @code{nil}. It does nothing else. In particular, it does not move point, which it does as a side effect if it finds the search target. After the @code{re-search-forward} expression returns @code{nil}, the next expression in the @code{while} loop is evaluated. This expression increments the count. Then the loop repeats. The true-or-false-test tests true because the value of point is still less than the value of end, since the @code{re-search-forward} expression did not move point. @dots{} and the cycle repeats @dots{} The @code{count-words-region} definition requires yet another modification, to cause the true-or-false-test of the @code{while} loop to test false if the search fails. Put another way, there are two conditions that must be satisfied in the true-or-false-test before the word count variable is incremented: point must still be within the region and the search expression must have found a word to count. Since both the first condition and the second condition must be true together, the two expressions, the region test and the search expression, can be joined with an @code{and} function and embedded in the @code{while} loop as the true-or-false-test, like this: @example (and (< (point) end) (re-search-forward "\\w+\\W*" end t)) @end example @c colon in printed section title causes problem in Info cross reference @c also trouble with an overfull hbox @iftex @noindent (For information about @code{and}, see @ref{forward-paragraph, , @code{forward-paragraph}: a Goldmine of Functions}.) @end iftex @ifinfo @noindent (@xref{forward-paragraph}, for information about @code{and}.) @end ifinfo The @code{re-search-forward} expression returns @code{t} if the search succeeds and as a side effect moves point. Consequently, as words are found, point is moved through the region. When the search expression fails to find another word, or when point reaches the end of the region, the true-or-false-test tests false, the @code{while} loop exists, and the @code{count-words-region} function displays one or other of its messages. After incorporating these final changes, the @code{count-words-region} works without bugs (or at least, without bugs that I have found!). Here is what it looks like: @example @group ;;; @r{Final version:} @code{while} (defun count-words-region (beginning end) "Print number of words in the region." (interactive "r") (message "Counting words in region ... ") @end group @group ;;; @r{1. Set up appropriate conditions.} (save-excursion (let ((count 0)) (goto-char beginning) @end group @group ;;; @r{2. Run the} while @r{loop.} (while (and (< (point) end) (re-search-forward "\\w+\\W*" end t)) (setq count (1+ count))) @end group @group ;;; @r{3. Send a message to the user.} (cond ((zerop count) (message "The region does NOT have any words.")) ((= 1 count) (message "The region has 1 word.")) (t (message "The region has %d words." count)))))) @end group @end example @node recursive-count-words, Counting Exercise, count-words-region, Counting Words @comment node-name, next, previous, up @section Count Words Recursively @cindex Count words recursively @cindex Recursively counting words @cindex Words, counted recursively You can write the function for counting words recursively as well as with a @code{while} loop. Let's see how this is done. First, we need to recognize that the @code{count-words-region} function has three jobs: it sets up the appropriate conditions for counting to occur; it counts the words in the region; and it sends a message to the user telling how many words there are. If we write a single recursive function to do everything, we will receive a message for every recursive call. If the region contains 13 words, we will receive thirteen messages, one right after the other. We don't want this! Instead, we must write two functions to do the job, one of which (the recursive function) will be used inside of the other. One function will set up the conditions and display the message; the other will return the word count. Let us start with the function that causes the message to be displayed. We can continue to call this @code{count-words-region}. This is the function that the user will call. It will be interactive. Indeed, it will be similar to our previous versions of this function, except that it will call @code{recursive-count-words} to determine how many words are in the region. We can readily construct a template for this function, based on our previous versions: @example @group ;; @r{Recursive version; uses regular expression search} (defun count-words-region (beginning end) "@var{documentation}@dots{}" (@var{interactive-expression}@dots{}) @end group @group ;;; @r{1. Set up appropriate conditions.} (@var{explanatory message}) (@var{set-up functions}@dots{} @end group @group ;;; @r{2. Count the words.} @var{recursive call} @end group @group ;;; @r{3. Send a message to the user.} @var{message providing word count})) @end group @end example The definition looks straightforward, except that somehow, the count returned by the recursive call must be passed to the message displaying the word count. A little thought suggests that this can be done by making use of a @code{let} expression: we can bind a variable in the varlist of a @code{let} expression to the number of words in the region, as returned by the recursive call; and then the @code{cond} expression, using binding, can display the value to the user. Often, one thinks of the binding within a @code{let} expression as somehow secondary to the `primary' work of a function. But in this case, what you might consider the `primary' job of the function, counting words, is done within the @code{let} expression. @need 1250 Using @code{let}, the function definition looks like this: @example @group (defun count-words-region (beginning end) "Print number of words in the region." (interactive "r") @end group @group ;;; @r{1. Set up appropriate conditions.} (message "Counting words in region ... ") (save-excursion (goto-char beginning) @end group @group ;;; @r{2. Count the words.} (let ((count (recursive-count-words end))) @end group @group ;;; @r{3. Send a message to the user.} (cond ((zerop count) (message "The region does NOT have any words.")) ((= 1 count) (message "The region has 1 word.")) (t (message "The region has %d words." count)))))) @end group @end example Next, we need to write the recursive counting function. A recursive function has at least three parts: the `do-again-test', the `next-step-expression', and the recursive call. The do-again-test determines whether the function will or will not be called again. Since we are counting words in a region and can use a function that moves point forward for every word, the do-again-test can check whether point is still within the region. The do-again-test should find the value of point and determine whether point is before, at, or after the value of the end of the region. We can use the @code{point} function to locate point. Clearly, we must pass the value of the end of the region to the recursive counting function as an argument. In addition, the do-again-test should also test whether the search finds a word. If it does not, the function should not call itself again. The next-step-expression changes a value so that when the recursive function is supposed to stop calling itself, it stops. More precisely, the next-step-expression changes a value so that at the right time, the do-again-test stops the recursive function from calling itself again. In this case, the next-step-expression can be the expression that moves point forward word by word. The third part of a recursive function is the recursive call. Somewhere, also, we also need a part that does the `work' of the function, a part that does the counting. A vital part! @need 1250 But already, we have an outline of the recursive counting function: @example @group (defun recursive-count-words (region-end) "@var{documentation}@dots{}" @var{do-again-test} @var{next-step-expression} @var{recursive call}) @end group @end example Now we need to fill in the slots. Let's start with the simplest cases first: if point is at or beyond the end of the region, there cannot be any words in the region, so the function should return zero. Likewise, if the search fails, there are no words to count, so the function should return zero. On the other hand, if point is within the region and the search succeeds, the function should call itself again. Thus, the do-again-test should look like this: @example @group (and (< (point) region-end) (re-search-forward "\\w+\\W*" region-end t)) @end group @end example Note that the search expression is part of the do-again-test---the function returns @code{t} if its search succeeds and @code{nil} if it fails. (@xref{Whitespace Bug, , The Whitespace Bug in @code{count-words-region}}, for an explanation of how @code{re-search-forward} works.) The do-again-test is the true-or-false test of an @code{if} clause. Clearly, if the do-again-test succeeds, the then-part of the @code{if} clause should call the function again; but if it fails, the else-part should return zero since either point is outside the region or the search failed because there were not words to find. But before considering the recursive call, we need to consider the next-step-expression. What is it? Interestingly, it is the search part of the do-again-test. In addition to returning @code{t} or @code{nil} for the do-again-test, @code{re-search-forward} moves point forward as a side effect of a successful search. This is the action that changes the value of point so that the recursive function stops calling itself when point completes its movement through the region. Consequently, the @code{re-search-forward} expression is the next-step-expression. In outline, then, the body of the @code{recursive-count-words} function looks like this: @example @group (if @var{do-again-test-and-next-step-combined} ;; @r{then} @var{recursive-call-returning-count} ;; @r{else} @var{return-zero}) @end group @end example How to incorporate the mechanism that counts? If you are not used to writing recursive functions, a question like this can be troublesome. But it can and should be approached systematically. We know that the counting mechanism should be associated in some way with the recursive call. Indeed, since the next-step-expression moves point forward by one word, and since a recursive call is made for each word, the counting mechanism must be an expression that adds one to the value returned by a call to @code{recursive-count-words}. Consider several cases: @itemize @bullet @item If there are two words in the region, the function should return a value resulting from adding one to the value returned when it counts the first word, plus the number returned when it counts the remaining words in the region, which in this case is one. @item If there is one word in the region, the function should return a value resulting from adding one to the value returned when it counts that word, plus the number returned when it counts the remaining words in the region, which in this case is zero. @item If there are no words in the region, the function should return zero. @end itemize From the sketch we can see that the else-part of the @code{if} returns zero for the case of no words. This means that the then-part of the @code{if} must return a value resulting from adding one to the value returned from a count of the remaining words. The expression will look like this, where @code{1+} is a function that adds one to its argument. @example (1+ (recursive-count-words region-end)) @end example The whole @code{recursive-count-words} function will then look like this: @example @group (defun recursive-count-words (region-end) "@var{documentation}@dots{}" ;;; @r{1. do-again-test} (if (and (< (point) region-end) (re-search-forward "\\w+\\W*" region-end t)) @end group @group ;;; @r{2. then-part: the recursive call} (1+ (recursive-count-words region-end)) ;;; @r{3. else-part} 0)) @end group @end example @need 1250 Let's examine how this works: If there are no words in the region, the else part of the @code{if} expression is evaluated and consequently the function returns zero. If there is one word in the region, the value of point is less than the value of @code{region-end} and the search succeeds. In this case, the true-or-false-test of the @code{if} expression tests true, and the then-part of the @code{if} expression is evaluated. The counting expression is evaluated. This expression returns a value (which will be the value returned by the whole function) that is the sum of one added to the value returned by a recursive call. Meanwhile, the next-step-expression has caused point to jump over the first (and in this case only) word in the region. This means that when @code{(recursive-count-words region-end)} is evaluated a second time, as a result of the recursive call, the value of point will be equal to or greater than the value of region end. So this time, @code{recursive-count-words} will return zero. The zero will be added to one, and the original evaluation of @code{recursive-count-words} will return one plus zero, which is one, which is the correct amount. Clearly, if there are two words in the region, the first call to @code{recursive-count-words} returns one added to the value returned by calling @code{recursive-count-words} on a region containing the remaining word---that is, it adds one to one, producing two, which is the correct amount. Similarly, if there are three words in the region, the first call to @code{recursive-count-words} returns one added to the value returned by calling @code{recursive-count-words} on a region containing the remaining two words---and so on and so on. @need 1250 With full documentation the two functions look like this: @need 1250 @noindent The recursive function: @findex recursive-count-words @example @group (defun recursive-count-words (region-end) "Number of words between point and REGION-END." @end group @group ;;; @r{1. do-again-test} (if (and (< (point) region-end) (re-search-forward "\\w+\\W*" region-end t)) @end group @group ;;; @r{2. then-part: the recursive call} (1+ (recursive-count-words region-end)) ;;; @r{3. else-part} 0)) @end group @end example @noindent The wrapper: @example @group ;;; @r{Recursive version} (defun count-words-region (beginning end) "Print number of words in the region. @end group @group Words are defined as at least one word-constituent character followed by at least one character that is not a word-constituent. The buffer's syntax table determines which characters these are." @end group @group (interactive "r") (message "Counting words in region ... ") (save-excursion (goto-char beginning) (let ((count (recursive-count-words end))) @end group @group (cond ((zerop count) (message "The region does NOT have any words.")) @end group @group ((= 1 count) (message "The region has 1 word.")) (t (message "The region has %d words." count)))))) @end group @end example @node Counting Exercise, , recursive-count-words, Counting Words @section Exercise: Counting Punctuation Using a @code{while} loop, write a function to count the number of punctuation marks in a region---period, comma, semicolon, colon, exclamation mark, question mark. Do the same using recursion. @node Words in a defun, Readying a Graph, Counting Words, Top @chapter Counting Words in a @code{defun} @cindex Counting words in a @code{defun} @cindex Word counting in a @code{defun} Our next project is to count the number of words in a function definition. Clearly, this can be done using some variant of @code{count-word-region}. @xref{Counting Words, , Counting Words: Repetition and Regexps}. If we are just going to count the words in one definition, it is easy enough to mark the definition with the @kbd{C-M-h} (@code{mark-defun}) command, and then call @code{count-word-region}. However, I am more ambitious: I want to count the words and symbols in every definition in the Emacs sources and then print a graph that shows how many functions there are of each length: how many contain 40 to 49 words or symbols, how many contain 50 to 59 words or symbols, and so on. I have often been curious how long a typical function is, and this will tell. @menu * Divide and Conquer:: Split a daunting project into parts. * Words and Symbols:: What to count? * Syntax:: What constitutes a word or symbol? * count-words-in-defun:: Very like @code{count-words}. * Several defuns:: Counting several defuns in a file. * Find a File:: Do you want to look at a file? * lengths-list-file:: A list of the lengths of many definitions. * Several files:: Counting in definitions in different files. * Several files recursively:: Recursively counting in different files. * Prepare the data:: Prepare the data for display in a graph. @end menu @node Divide and Conquer, Words and Symbols, Words in a defun, Words in a defun @ifinfo @heading Divide and Conquer @end ifinfo Described in one phrase, the histogram project is daunting; but divided into numerous small steps, each of which we can take one at a time, the project becomes less fearsome. Let us consider what the steps must be: @itemize @bullet @item First, write a function to count the words in one definition. This includes the problem of handling symbols as well as words. @item Second, write a function to list the numbers of words in each function in a file. This function can use the @code{count-words-in-defun} function. @item Third, write a function to list the numbers of words in each function in each of several files. This entails automatically finding the various files, switching to them, and counting the words in the definitions within them. @item Fourth, write a function to convert the list of numbers that we created in step three to a form that will be suitable for printing as a graph. @item Fifth, write a function to print the results as a graph. @end itemize This is quite a project! But if we take each step slowly, it will not be difficult. @node Words and Symbols, Syntax, Divide and Conquer, Words in a defun @section What to Count? @cindex Words and symbols in defun When we first start thinking about how to count the words in a function definition, the first question is (or ought to be) what are we going to count? When we speak of `words' with respect to a Lisp function definition, we are actually speaking, in large part, of `symbols'. For example, the following @code{multiply-by-seven} function contains the five symbols @code{defun}, @code{multiply-by-seven}, @code{number}, @code{*}, and @code{7}. In addition, in the documentation string, it contains the four words @samp{Multiply}, @samp{NUMBER}, @samp{by}, and @samp{seven}. The symbol @samp{number} is repeated, so the definition contains a total of ten words and symbols. @example @group (defun multiply-by-seven (number) "Multiply NUMBER by seven." (* 7 number)) @end group @end example @noindent However, if we mark the @code{multiply-by-seven} definition with @kbd{C-M-h} (@code{mark-defun}), and then call @code{count-words-region} on it, we will find that @code{count-words-region} claims the definition has eleven words, not ten! Something is wrong! The problem is twofold: @code{count-words-region} does not count the @samp{*} as a word, and it counts the single symbol, @code{multiply-by-seven}, as containing three words. The hyphens are treated as if they were interword spaces rather than intraword connectors: @samp{multiply-by-seven} is counted as if it were written @samp{multiply by seven}. The cause of this confusion is the regular expression search within the @code{count-words-region} definition that moves point forward word by word. In the canonical version of @code{count-words-region}, the regexp is: @example "\\w+\\W*" @end example @noindent This regular expression is a pattern defining one or more word constituent characters possibly followed by one or more characters that are not word constituents. What is meant by `word constituent characters' brings us to the issue of syntax, which is worth a section of its own. @node Syntax, count-words-in-defun, Words and Symbols, Words in a defun @section What Constitutes a Word or Symbol? @cindex Syntax categories and tables Emacs treats different characters as belonging to different @dfn{syntax categories}. For example, the regular expression, @samp{\\w+}, is a pattern specifying one or more @emph{word constituent} characters. Word constituent characters are members of one syntax category. Other syntax categories include the class of punctuation characters, such as the period and the comma, and the class of whitespace characters, such as the blank space and the tab character. (For more information, see @ref{Syntax, Syntax, The Syntax Table, emacs, The GNU Emacs Manual}, and, @ref{Syntax Tables, , Syntax Tables, elisp, The GNU Emacs Lisp Reference Manual}.) Syntax tables specify which characters belong to which categories. Usually, a hyphen is not specified as a `word constituent character'. Instead, it is specified as being in the `class of characters that are part of symbol names but not words.' This means that the @code{count-words-region} function treats it in the same way it treats an interword white space, which is why @code{count-words-region} counts @samp{multiply-by-seven} as three words. There are two ways to cause Emacs to count @samp{multiply-by-seven} as one symbol: modify the syntax table or modify the regular expression. We could redefine a hyphen as a word constituent character by modifying the syntax table that Emacs keeps for each mode. This action would serve our purpose, except that a hyphen is merely the most common character within symbols that is not typically a word constituent character; there are others, too. Alternatively, we can redefine the regular expression used in the @code{count-words} definition so as to include symbols. This procedure has the merit of clarity, but the task is a little tricky. The first part is simple enough: the pattern must match ``at least one character that is a word or symbol constituent''. Thus: @example \\(\\w\\|\\s_\\)+ @end example @noindent The @samp{\\(} is the first part of the grouping construct that includes the @samp{\\w} and the @samp{\\s_} as alternatives, separated by the @samp{\\|}. The @samp{\\w} matches any word-constituent character and the @samp{\\s_} matches any character that is part of a symbol name but not a word-constituent character. The @samp{+} following the group indicates that the word or symbol constituent characters must be matched at least once. However, the second part of the regexp is more difficult to design. What we want is to follow the first part with ``optionally one or more characters that are not constituents of a word or symbol''. At first, I thought I could define this with the following: @example \\(\\W\\|\\S_\\)*" @end example @noindent The upper case @samp{W} and @samp{S} match characters that are @emph{not} word or symbol constituents. Unfortunately, this expression matches any character that is either not a word constituent or not a symbol constituent. This matches any character! I then noticed that every word or symbol in my test region was followed by white space (blank space, tab, or newline). So I tried placing a pattern to match one or more blank spaces after the pattern for one or more word or symbol constituents. This failed, too. Words and symbols are often separated by whitespace, but in actual code parentheses may follow symbols and punctuation may follow words. So finally, I designed a pattern in which the word or symbol constituents are followed optionally by characters that are not white space and then followed optionally by white space. Here is the full regular expression: @example "\\(\\w\\|\\s_\\)+[^ \t\n]*[ \t\n]*" @end example @node count-words-in-defun, Several defuns, Syntax, Words in a defun @section The @code{count-words-in-defun} Function @cindex Counting words in a @code{defun} We have seen that there are several ways to write a @code{count-word-region} function. To write a @code{count-words-in-defun}, we need merely adapt one of these versions. The version that uses a @code{while} loop is easy to understand, so I am going to adapt that. Because @code{count-words-in-defun} will be part of a more complex program, it need not be interactive and it need not display a message but just return the count. These considerations simplify the definition a little. On the other hand, @code{count-words-in-defun} will be used within a buffer that contains function definitions. Consequently, it is reasonable to ask that the function determine whether it is called when point is within a function definition, and if it is, to return the count for that definition. This adds complexity to the definition, but saves us from needing to pass arguments to the function. @need 1250 These considerations lead us to prepare the following template: @example @group (defun count-words-in-defun () "@var{documentation}@dots{}" (@var{set up}@dots{} (@var{while loop}@dots{}) @var{return count}) @end group @end example @noindent As usual, our job is to fill in the slots. First, the set up. We are presuming that this function will be called within a buffer containing function definitions. Point will either be within a function definition or not. For @code{count-words-in-defun} to work, point must move to the beginning of the definition, a counter must start at zero, and the counting loop must stop when point reaches the end of the definition. The @code{beginning-of-defun} function searches backwards for an opening delimiter such as a @samp{(} at the beginning of a line, and moves point to that position, or else to the limit of the search. In practice, this means that @code{beginning-of-defun} moves point to the beginning of an enclosing or preceding function definition, or else to the beginning of the buffer. We can use @code{beginning-of-defun} to place point where we wish to start. The @code{while} loop requires a counter to keep track of the words or symbols being counted. A @code{let} expression can be used to create a local variable for this purpose, and bind it to an initial value of zero. The @code{end-of-defun} function works like @code{beginning-of-defun} except that it moves point to the end of the definition. @code{end-of-defun} can be used as part of an expression that determines the position of the end of the definition. The set up for @code{count-words-in-defun} takes shape rapidly: first we move point to the beginning of the definition, then we create a local variable to hold the count, and, finally, we record the position of the end of the definition so the @code{while} loop will know when to stop looping. @need 1250 The code looks like this: @example @group (beginning-of-defun) (let ((count 0) (end (save-excursion (end-of-defun) (point)))) @end group @end example @noindent The code is simple. The only slight complication is likely to concern @code{end}: it is bound to the position of the end of the definition by a @code{save-excursion} expression that returns the value of point after @code{end-of-defun} temporarily moves it to the end of the definition. The second part of the @code{count-words-in-defun}, after the set up, is the @code{while} loop. The loop must contain an expression that jumps point forward word by word and symbol by symbol, and another expression that counts the jumps. The true-or-false-test for the @code{while} loop should test true so long as point should jump forward, and false when point is at the end of the definition. We have already redefined the regular expression for this (@pxref{Syntax}), so the loop is straightforward: @example @group (while (and (< (point) end) (re-search-forward "\\(\\w\\|\\s_\\)+[^ \t\n]*[ \t\n]*" end t) (setq count (1+ count))) @end group @end example The third part of the function definition returns the count of words and symbols. This part is the last expression within the body of the @code{let} expression, and can be, very simply, the local variable @code{count}, which when evaluated returns the count. @need 1250 Put together, the @code{count-words-in-defun} definition looks like this: @findex count-words-in-defun @example @group (defun count-words-in-defun () "Return the number of words and symbols in a defun." (beginning-of-defun) (let ((count 0) (end (save-excursion (end-of-defun) (point)))) @end group @group (while (and (< (point) end) (re-search-forward "\\(\\w\\|\\s_\\)+[^ \t\n]*[ \t\n]*" end t)) (setq count (1+ count))) count)) @end group @end example How to test this? The function is not interactive, but it is easy to put a wrapper around the function to make it interactive; we can use almost the same code as for the recursive version of @code{count-words-region}: @example @group ;;; @r{Interactive version.} (defun count-words-defun () "Number of words and symbols in a function definition." (interactive) (message "Counting words and symbols in function definition ... ") @end group @group (let ((count (count-words-in-defun))) (cond ((zerop count) (message "The definition does NOT have any words or symbols.")) @end group @group ((= 1 count) (message "The definition has 1 word or symbol.")) (t (message "The definition has %d words or symbols." count))))) @end group @end example @noindent Let's re-use @kbd{C-c =} as a convenient keybinding: @example (global-set-key "\C-c=" 'count-words-defun) @end example Now we can try out @code{count-words-defun}: install both @code{count-words-in-defun} and @code{count-words-defun}, and set the keybinding, and then place the cursor within the following definition: @example @group (defun multiply-by-seven (number) "Multiply NUMBER by seven." (* 7 number)) @result{} 10 @end group @end example @noindent Success! The definition has 10 words and symbols. The next problem is to count the numbers of words and symbols in several definitions within a single file. @node Several defuns, Find a File, count-words-in-defun, Words in a defun @section Count Several @code{defuns} Within a File A file such as @file{simple.el} may have 80 or more function definitions within it. Our long term goal is to collect statistics on many files, but as a first step, our immediate goal is to collect statistics on one file. The information will be a series of numbers, each number being the length of a function definition. We can store the numbers in a list. We know that we will want to incorporate the information regarding one file with information about many other files; this means that the function for counting definition lengths within one file need only return the lengths' list. It need not and should not display any messages. The word count commands contain one expression to jump point forward word by word and another expression to count the jumps. The definitions' lengths' function can be designed to work the same way, with one expression to jump point forward definition by definition and another expression to construct the lengths' list. This statement of the problem makes it elementary to write the function definition. Clearly, we will start the count at the beginning of the file, so the first command will be @code{(goto-char (point-min))}. Next, we start the @code{while} loop; and the true-or-false test of the loop can be a regular expression search for the next function definition---so long as the search succeeds, point is moved forward and then the body of the loop is evaluated. The body needs an expression that constructs the lengths' list. @code{cons}, the list construction command, can be used to create the list. That is almost all there is to it. Here is what this fragment of code looks like: @example @group (goto-char (point-min)) (while (re-search-forward "^(defun" nil t) (setq lengths-list (cons (count-words-in-defun) lengths-list))) @end group @end example What we have left out is the mechanism for finding the file that contains the function definitions. In previous examples, we either used this, the Info file, or we switched back and forth to some other buffer, such as the @file{*scratch*} buffer. Finding a file is a new process that we have not yet discussed. @node Find a File, lengths-list-file, Several defuns, Words in a defun @comment node-name, next, previous, up @section Find a File @cindex Find a File To find a file in Emacs, you use the @kbd{C-x C-f} (@code{find-file}) command. This command is almost, but not quite right for the lengths problem. Let's look at the source for @code{find-file} (you can use the @code{find-tag} command to find the source of a function): @example @group (defun find-file (filename) "Edit file FILENAME. Switch to a buffer visiting file FILENAME, creating one if none already exists." (interactive "FFind file: ") (switch-to-buffer (find-file-noselect filename))) @end group @end example The definition possesses short but complete documentation and an interactive specification that prompts you for a file name when you use the command interactively. The body of the definition contains two functions, @code{find-file-noselect} and @code{switch-to-buffer}. According to its documentation as shown by @kbd{C-h f} (the @code{describe-function} command), the @code{find-file-noselect} function reads the named file into a buffer and returns the buffer. However, the buffer is not selected. Emacs does not switch its attention (or yours if you are using @code{find-file-noselect}) to the named buffer. That is what @code{switch-to-buffer} does: it switches the buffer to which Emacs attention is directed; and it switches the buffer displayed in the window to the new buffer. We have discussed buffer switching elsewhere. (@xref{Switching Buffers}.) In this histogram project, we do not need to display each file on the screen as the program determines the length of each definition within it. Instead of employing @code{switch-to-buffer}, we can work with @code{set-buffer}, which redirects the attention of the computer program to a different buffer but does not redisplay it on the screen. So instead of calling on @code{find-file} to do the job, we must write our own expression. The task is easy: use @code{find-file-noselect} and @code{set-buffer}. @node lengths-list-file, Several files, Find a File, Words in a defun @section @code{lengths-list-file} in Detail The core of the @code{lengths-list-file} function is a @code{while} loop containing a function to move point forward `defun by defun' and a function to count the number of words and symbols in each defun. This core must be surrounded by functions that do various other tasks, including finding the file, and ensuring that point starts out at the beginning of the file. The function definition looks like this: @findex lengths-list-file @example @group (defun lengths-list-file (filename) "Return list of definitions' lengths within FILE. The returned list is a list of numbers. Each number is the number of words or symbols in one function definition." @end group @group (message "Working on `%s' ... " filename) (save-excursion (let ((buffer (find-file-noselect filename)) (lengths-list)) (set-buffer buffer) (setq buffer-read-only t) (widen) (goto-char (point-min)) (while (re-search-forward "^(defun" nil t) (setq lengths-list (cons (count-words-in-defun) lengths-list))) (kill-buffer buffer) lengths-list))) @end group @end example @noindent The function is passed one argument, the name of the file on which it will work. It has four lines of documentation, but no interactive specification. Since people worry that a computer is broken if they don't see anything going on, the first line of the body is a message. The next line contains a @code{save-excursion} that returns Emacs attention to the current buffer when the function completes. This is useful in case you embed this function in another function that presumes point is restored to the original buffer. In the varlist of the @code{let} expression, Emacs finds the file and binds the local variable @code{buffer} to the buffer containing the file. At the same time, Emacs creates @code{lengths-list} as a local variable. Next, Emacs switches its attention to the buffer. In the following line, Emacs makes the buffer read-only. Ideally, this line is not necessary. None of the functions for counting words and symbols in a function definition should change the buffer. Besides, the buffer is not going to be saved, even if it were changed. This line is entirely the consequence of great, perhaps excessive, caution. The reason for the caution is that this function and those it calls work on the sources for Emacs and it is very inconvenient if they are inadvertently modified. It goes without saying that I did not realize a need for this line until an experiment went awry and started to modify my Emacs source files @dots{} Next comes a call to widen the buffer if it is narrowed. This function is usually not needed---Emacs creates a fresh buffer if none already exists; but if a buffer visiting the file already exists Emacs returns that one. In this case, the buffer may be narrowed and must be widened. If we wanted to be fully `user-friendly', we would arrange to save the restriction and the location of point, but we won't. The @code{(goto-char (point-min))} expression moves point to the beginning of the buffer. Then comes a @code{while} loop in which the `work' of the function is carried out. In the loop, Emacs determines the length of each definition and constructs a lengths' list containing the information. Emacs kills the buffer after working through it. This is to save space inside of Emacs. My version of Emacs 19 contains over 300 source files of interest. Another function will apply @code{lengths-list-file} to each of them. If Emacs visits all of them and deletes none, my computer may run out of virtual memory. Finally, the last expression within the @code{let} expression is the @code{lengths-list} variable; its value is returned as the value of the whole function. You can try this function by installing it in the usual fashion. Then place your cursor after the following expression and type @kbd{C-x C-e} (@code{eval-last-sexp}). @example (lengths-list-file "../lisp/debug.el") @end example @c (lengths-list-file "/usr/local/emacs/lisp/debug.el") @noindent (You may need to change the pathname of the file; the one here works if this Info file and the Emacs sources are in neighboring places, such as @code{/usr/local/emacs/info} and @code{/usr/local/emacs/lisp}. To change the expression, copy it to the @file{*scratch*} buffer and edit it. Then evaluate it.) @need 1500 On my version of Emacs, the lengths' list for @file{debug.el} takes seven seconds to produce and looks like this: @example (75 41 80 62 20 45 44 68 45 12 34 235) @end example Note that the length of the last definition in the file is first in the list. @node Several files, Several files recursively, lengths-list-file, Words in a defun @section Count Words in @code{defuns} in Different Files In the previous section, we created a function that returns a list of the lengths of each definition in a file. Now, we want to define a function to return a master list of the lengths of the definitions in a list of files. Working on each of a list of files is a repetitious act, so we can use either a @code{while} loop or recursion. The design using a @code{while} loop is routine. The argument passed the function is a list of files. As we saw earlier (@pxref{Loop Example}), you can write a @code{while} loop so that the body of the loop is evaluated if such a list contains elements, but to exit the loop if the list is empty. For this design to work, the body of the loop must contain an expression that shortens the list each time the body is evaluated, so that eventually the list is empty. The usual technique is to set the value of the list to the value of the @sc{cdr} of the list each time the body is evaluated. The template looks like this: @example @group (while @var{test-whether-list-is-empty} @var{body}@dots{} @var{set-list-to-cdr-of-list}) @end group @end example Also, we remember that a @code{while} loop returns @code{nil} (the result of evaluating the true-or-false-test), not the result of any evaluation within its body. (The evaluations within the body of the loop are done for their side effects.) However, the expression that sets the lengths' list is part of the body---and that is the value that we want returned by the function as a whole. To do this, we enclose the @code{while} loop within a @code{let} expression, and arrange that the last element of the @code{let} expression contains the value of the lengths' list. (@xref{Incrementing Example, , Loop Example with an Incrementing Counter}.) @findex lengths-list-many-files @need 1250 These considerations lead us directly to the function itself: @example @group ;;; @r{Use @code{while} loop.} (defun lengths-list-many-files (list-of-files) "Return list of lengths of defuns in LIST-OF-FILES." @end group @group (let (lengths-list) ;;; @r{true-or-false-test} (while list-of-files (setq lengths-list (append lengths-list ;;; @r{Generate a lengths' list.} (lengths-list-file (expand-file-name (car list-of-files))))) @end group @group ;;; @r{Make files' list shorter.} (setq list-of-files (cdr list-of-files))) ;;; @r{Return final value of lengths' list.} lengths-list)) @end group @end example @code{expand-file-name} is a built-in function that converts a file name to its absolute, long, path name form. Thus, @example debug.el @end example @noindent becomes @example /usr/local/emacs/lisp/debug.el @end example The only other new element of this function definition is the as yet unstudied function @code{append}, which merits a short section for itself. @menu * append:: Attaching one list to another. @end menu @node append, , Several files, Several files @subsection The @code{append} Function The @code{append} function attaches one list to another. Thus, @example (append '(1 2 3 4) '(5 6 7 8)) @end example @noindent produces the list @example (1 2 3 4 5 6 7 8) @end example This is exactly how we want to attach two lengths' lists produced by @code{lengths-list-file} to each other. The results contrast with @code{cons}, @example (cons '(1 2 3 4) '(5 6 7 8)) @end example @noindent which constructs a new list in which the first argument to @code{cons} becomes the first element of the new list: @example ((1 2 3 4) 5 6 7 8) @end example @node Several files recursively, Prepare the data, Several files, Words in a defun @section Recursively Count Words in Different Files Besides a @code{while} loop, you can work on each of a list of files with recursion. A recursive version of @code{lengths-list-many-files} is short and simple. The recursive function has the usual parts: the `do-again-test', the `next-step-expression', and the recursive call. The `do-again-test' determines whether the function should call itself again, which it will do if the @code{list-of-files} contains any remaining elements; the `next-step-expression' resets the @code{list-of-files} to the @sc{cdr} of itself, so eventually the list will be empty; and the recursive call calls itself on the shorter list. The complete function is shorter than this description! @findex recursive-lengths-list-many-files @example @group (defun recursive-lengths-list-many-files (list-of-files) "Return list of lengths of each defun in LIST-OF-FILES." (if list-of-files ; @r{do-again-test} (append (lengths-list-file (expand-file-name (car list-of-files))) (recursive-lengths-list-many-files (cdr list-of-files))))) @end group @end example @noindent In a sentence, the function returns the lengths' list for the first of the @code{list-of-files} appended to the result of calling itself on the rest of the @code{list-of-files}. Here is a test of @code{recursive-lengths-list-many-files}, along with the results of running @code{lengths-list-file} on each of the files individually. Install @code{recursive-lengths-list-many-files} and @code{lengths-list-file}, if necessary, and then evaluate the following expressions. You may need to change the files' pathnames; those here work when this Info file and the Emacs sources are located in their customary places. To change the expressions, copy them to the @file{*scratch*} buffer, edit them, and then evaluate them. The results are shown after the @samp{@result{}}. (These results are for files from Emacs Version 18.57; files from other versions of Emacs may produce different results.) @example @group (lengths-list-file "../lisp/macros.el") @result{} (176 154 86) @end group @group (lengths-list-file "../lisp/mailalias.el") @result{} (116 122 265) @end group @group (lengths-list-file "../lisp/makesum.el") @result{} (85 179) @end group @group (recursive-lengths-list-many-files '("../lisp/macros.el" "../lisp/mailalias.el" "../lisp/makesum.el")) @result{} (176 154 86 116 122 265 85 179) @end group @end example The @code{recursive-lengths-list-many-files} function produces the output we want. The next step is to prepare the data in the list for display in a graph. @node Prepare the data, , Several files recursively, Words in a defun @section Prepare the Data for Display in a Graph The @code{recursive-lengths-list-many-files} function returns a list of numbers. Each number records the length of a function definition. What we need to do now is transform this data into a list of numbers suitable for generating a graph. The new list will tell how many functions definitions contain less than 10 words and symbols, how many contain between 10 and 19 words and symbols, how many contain between 20 and 29 words and symbols, and so on. In brief, we need to go through the lengths' list produced by the @code{recursive-lengths-list-many-files} function and count the number of defuns within each range of lengths, and produce a list of those numbers. Based on what we have done before, we can readily foresee that it should not be too hard to write a function that `@sc{cdr}s' down the lengths' list, looks at each element, determines which length range it is in, and increments a counter for that range. However, before beginning to write such a function, we should consider the advantages of sorting the lengths' list first, so the numbers are ordered from smallest to largest. First, sorting will make it easier to count the numbers in each range, since two adjacent numbers will either be in the same length range or in adjacent ranges. Second, by inspecting a sorted list, we can discover the highest and lowest number, and thereby determine the largest and smallest length range that we will need. @menu * Sorting:: Sorting lists. * Files List:: Making a list of files. @end menu @node Sorting, Files List, Prepare the data, Prepare the data @subsection Sorting Lists @findex sort Emacs contains a function to sort lists, called (as you might guess) @code{sort}. The @code{sort} function takes two arguments, the list to be sorted, and a predicate that determines whether the first of two list elements is ``less'' than the second. As we saw earlier (@pxref{Wrong Type of Argument, , Using the Wrong Type Object as an Argument}), a predicate is a function that determines whether some property is true or false. The @code{sort} function will reorder a list according to whatever property the predicate uses; this means that @code{sort} can be used to sort non-numeric lists by non-numeric criteria---it can, for example, alphabetize a list. @need 1250 The @code{<} function is used when sorting a numeric list. For example, @example (sort '(4 8 21 17 33 7 21 7) '<) @end example @noindent produces this: @example (4 7 7 8 17 21 21 33) @end example @noindent (Note that in this example, both the arguments are quoted so that the symbols are not evaluated before being passed to @code{sort} as arguments.) Sorting the list returned by the @code{recursive-lengths-list-many-files} function is straightforward: @example @group (sort (recursive-lengths-list-many-files '("../lisp/macros.el" "../lisp/mailalias.el" "../lisp/makesum.el")) '<) @end group @end example @noindent which produces: @example (85 86 116 122 154 176 179 265) @end example @noindent (Note that in this example, the first argument to @code{sort} is not quoted, since the expression must be evaluated so as to produce the list that is passed to @code{sort}.) @node Files List, , Sorting, Prepare the data @subsection Making a List of Files The @code{recursive-lengths-list-many-files} function requires a list of files as its argument. For our test examples, we constructed such a list by hand; but the Emacs Lisp source directory is too large for us to do for that. Instead, we need to use the @code{directory-files} function to construct a list for us. @findex directory-files The @code{directory-files} function takes three arguments: the first argument is the name of a directory, a string; a non-@code{nil} second argument causes the function to return the files' absolute pathnames; and the third argument is a selector. If it contains a regular expression (rather than @code{nil}), only pathnames that match that regular expression are returned. @need 1250 Thus, on my system, @example @group (length (directory-files "../lisp" t "\\.el$")) @end group @end example @noindent tells me that my version 19.25 Lisp sources directory contains 307 @samp{.el} files. An expression to sort the list returned by @code{recursive-lengths-list-many-files} looks like this: @example @group (sort (recursive-lengths-list-many-files (directory-files "../lisp" t "\\.el$")) '<) @end group @end example @ignore (defun test () "Test how long it takes to find lengths of all elisp defuns." (insert "\n" (current-time-string) "\n") (sit-for 0) (sort (recursive-lengths-list-many-files '("../lisp/macros.el" "../lisp/mailalias.el" "../lisp/makesum.el")) '<) (insert (format "%s" (current-time-string)))) @end ignore Our immediate goal is to generate a list that tells us how many function definitions contain fewer than 10 words and symbols, how many contain between 10 and 19 words and symbols, how many contain between 20 and 29 words and symbols, and so on. With a sorted list of numbers, this is easy: count how many elements of the list are smaller than 10, then, after moving past the numbers just counted, count how many are smaller than 20, then, after moving past the numbers just counted, count how many are smaller than 30, and so on. Each of the numbers, 10, 20, 30, 40, and the like, is one larger than the top of that range. We can call the list of such numbers the @code{top-of-ranges} list. If we wanted to, we could generate this list automatically, but it is simpler to write a list manually. Here it is: @vindex top-of-ranges @example @group (defvar top-of-ranges '(10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300) "List specifying ranges for `defuns-per-range'.") @end group @end example To change the ranges, we edit this list. Next, we need to write the function that creates the list of the number of definitions within each range. Clearly, this function must take the @code{sorted-lengths} and the @code{top-of-ranges} lists as arguments. The @code{defuns-per-range} function must do two things again and again: it must count the number of definitions within a range specified by the current top-of-range value; and it must shift to the next higher value in the @code{top-of-ranges} list after counting the number of definitions in the current range. Since each of these actions is repetitive, we can use @code{while} loops for the job. One loop counts the number of definitions in the range defined by the current top-of-range value, and the other loop selects each of the top-of-range values in turn. Several entries of the @code{sorted-lengths} list are counted for each range; this means that the loop for the @code{sorted-lengths} list will be inside the loop for the @code{top-of-ranges} list, like a small gear inside a big gear. The inner loop counts the number of definitions within the range. It is a simple counting loop of the type we have seen before. (@xref{Incrementing Loop, , A loop with an incrementing counter}.) The true-or-false test of the loop tests whether the value from the @code{sorted-lengths} list is smaller than the current value of the top of the range. If it is, the function increments the counter and tests the next value from the @code{sorted-lengths} list. @need 1250 The inner loop looks like this: @example @group (while @var{length-element-smaller-than-top-of-range} (setq number-within-range (1+ number-within-range)) (setq sorted-lengths (cdr sorted-lengths))) @end group @end example The outer loop must start with the lowest value of the @code{top-of-ranges} list, and then be set to each of the succeeding higher values in turn. This can be done with a loop like this: @example @group (while top-of-ranges @var{body-of-loop}@dots{} (setq top-of-ranges (cdr top-of-ranges))) @end group @end example Put together, the two loops look like this: @example @group (while top-of-ranges ;; @r{Count the number of elements within the current range.} (while @var{length-element-smaller-than-top-of-range} (setq number-within-range (1+ number-within-range)) (setq sorted-lengths (cdr sorted-lengths))) ;; @r{Move to next range.} (setq top-of-ranges (cdr top-of-ranges))) @end group @end example In addition, in each circuit of the outer loop, Emacs should record the number of definitions within that range (the value of @code{number-within-range}) in a list. We can use @code{cons} for this purpose. (@xref{cons, , @code{cons}}.) The @code{cons} function works fine, except that the list it constructs will contain the number of definitions for the highest range at its beginning and the number of definitions for the lowest range at its end. This is because @code{cons} attaches new elements of the list to the beginning of the list, and since the two loops are working their way through the lengths' list from the lower end first, the @code{defuns-per-range-list} will end up largest number first. But we will want to print our graph with smallest values first and the larger later. The solution is to reverse the order of the @code{defuns-per-range-list}. We can do this using the @code{nreverse} function, which reverses the order of a list. @findex nreverse For example, @example (nreverse '(1 2 3 4)) @end example @noindent produces: @example (4 3 2 1) @end example Note that the @code{nreverse} function is ``destructive''---that is, it changes the list to which it is applied; this contrasts with the @code{car} and @code{cdr} functions, which are non-destructive. In this case, we do not want the original @code{defuns-per-range-list}, so it does not matter that it is destroyed. (The @code{reverse} function provides a reversed copy of a list, leaving the original list as is.) @findex reverse @need 1250 Put all together, the @code{defuns-per-range} looks like this: @example @group (defun defuns-per-range (sorted-lengths top-of-ranges) "SORTED-LENGTHS defuns in each TOP-OF-RANGES range." (let ((top-of-range (car top-of-ranges)) (number-within-range 0) defuns-per-range-list) @end group @group ;; @r{Outer loop.} (while top-of-ranges @end group @group ;; @r{Inner loop.} (while (and ;; @r{Need number for numeric test.} (car sorted-lengths) (< (car sorted-lengths) top-of-range)) @end group @group ;; @r{Count number of definitions within current range.} (setq number-within-range (1+ number-within-range)) (setq sorted-lengths (cdr sorted-lengths))) ;; @r{Exit inner loop but remain within outer loop.} @end group @group (setq defuns-per-range-list (cons number-within-range defuns-per-range-list)) (setq number-within-range 0) ; @r{Reset count to zero.} @end group @group ;; @r{Move to next range.} (setq top-of-ranges (cdr top-of-ranges)) ;; @r{Specify next top of range value.} (setq top-of-range (car top-of-ranges))) @end group @group ;; @r{Exit outer loop and count the number of defuns larger than} ;; @r{ the largest top-of-range value.} (setq defuns-per-range-list (cons (length sorted-lengths) defuns-per-range-list)) @end group @group ;; @r{Return a list of the number of definitions within each range,} ;; @r{ smallest to largest.} (nreverse defuns-per-range-list))) @end group @end example @noindent The function is straightforward except for one subtle feature. The true-or-false test of the inner loop looks like this: @example @group (and (car sorted-lengths) (< (car sorted-lengths) top-of-range)) @end group @end example @noindent instead of like this: @example (< (car sorted-lengths) top-of-range) @end example The purpose of the test is to determine whether the first item in the @code{sorted-lengths} list is less than the value of the top of the range. The simple version of the test works fine unless the @code{sorted-lengths} list has a @code{nil} value. In that case, the @code{(car sorted-lengths)} expression function returns @code{nil}. The @code{<} function cannot compare a number to @code{nil}, which is an empty list, so Emacs signals an error and stops the function from attempting to continue to execute. The @code{sorted-lengths} list always becomes @code{nil} when the counter reaches the end of the list. This means that any attempt to use the @code{defuns-per-range} function with the simple version of the test will fail. We solve the problem by using the @code{(car sorted-lengths)} expression in conjunction with the @code{and} expression. The @code{(car sorted-lengths)} expression returns a non-@code{nil} value so long as the list has at least one number within it, but returns @code{nil} if the list is empty. The @code{and} expression first evaluates the @code{(car sorted-lengths)} expression, and if it is @code{nil}, returns false @emph{without} evaluating the @code{<} expression. But if the @code{(car sorted-lengths)} expression returns a non-@code{nil} value, the @code{and} expression evaluates the @code{<} expression, and returns that value as the value of the @code{and} expression. @c colon in printed section title causes problem in Info cross reference This way, we avoid an error. @iftex @xref{forward-paragraph, , @code{forward-paragraph}: a Goldmine of Functions}, for more information about @code{and}. @end iftex @ifinfo @xref{forward-paragraph}, for more information about @code{and}. @end ifinfo Here is a short test of the @code{defuns-per-range} function. First, evaluate the expression that binds (a shortened) @code{top-of-ranges} list to the list of values, then evaluate the expression for binding the @code{sorted-lengths} list, and then evaluate the @code{defuns-per-range} function. @example @group ;; @r{(Shorter list than we will use later.)} (setq top-of-ranges '(110 120 130 140 150 160 170 180 190 200)) (setq sorted-lengths '(85 86 110 116 122 129 154 176 179 200 265 300 300)) (defuns-per-range sorted-lengths top-of-ranges) @end group @end example @noindent The list returned looks like this: @example (2 2 2 0 0 1 0 2 0 0 4) @end example @noindent Indeed, there are two elements of the @code{sorted-lengths} list smaller than 110, two elements between 110 and 119, two elements between 120 and 129, and so on. There are four elements with a value of 200 or larger. @c The next step is to turn this numbers' list into a graph. @node Readying a Graph, Emacs Initialization, Words in a defun, Top @chapter Readying a Graph @cindex Readying a graph @cindex Graph prototype @cindex Prototype graph @cindex Body of graph Our goal is to construct a graph showing the numbers of function definitions of various lengths in the Emacs lisp sources. As a practical matter, if you were creating a graph, you would probably use a program such as @code{gnuplot} to do the job. (@code{gnuplot} is nicely integrated into GNU Emacs.) In this case, however, we create one from scratch, and in the process we will reaquaint ourselves with some of what we learned before and learn more. In this chapter, we will first write a simple graph printing function. This first definition will be a @dfn{prototype}, a rapidly written function that enables us to reconnoiter this unknown graph-making territory. We will discover dragons, or find that they are myth. After scouting the terrain, we will feel more confident and enhance the function to label the axes automatically. @menu * Columns of a graph:: How to print individual columns. * graph-body-print:: How to print the body of a graph. * recursive-graph-body-print:: * Printed Axes:: * Line Graph Exercise:: @end menu @node Columns of a graph, graph-body-print, Readying a Graph, Readying a Graph @ifinfo @heading Printing the Columns of a Graph @end ifinfo Since Emacs is designed to be flexible and work with all kinds of terminals, including character-only terminals, the graph will need to be made from one of the `typewriter' symbols. An asterisk will do; as we enhance the graph-printing function, we can make the choice of symbol a user option. We can call this function @code{graph-body-print}; it will take a @code{numbers-list} as its only argument. At this stage, we will not label the graph, but only print its body. The @code{graph-body-print} function inserts a vertical column of asterisks for each element in the @code{numbers-list}. The height of each line is determined by the value of that element of the @code{numbers-list}. Inserting columns is a repetitive act; that means that this function can be written either with a @code{while} loop or recursively. Our first challenge is to discover how to print a column of asterisks. Usually, in Emacs, we print characters onto a screen horizontally, line by line, by typing. We have two routes we can follow: write our own column-insertion function or discover whether one exists in Emacs. To see whether there is one in Emacs, we can use the @kbd{M-x apropos} command. This command is like the @kbd{C-h a} (command-apropos) command, except that the latter finds only those functions that are commands. The @kbd{M-x apropos} command lists all symbols that match a regular expression, including functions that are not interactive. @findex apropos What we want to look for is some command that prints or inserts columns. Very likely, the name of the function will contain either the word `print' or the word `insert' or the word `column'. Therefore, we can simply type @kbd{M-x apropos RET print\|insert\|column RET} and look at the result. On my system, this command takes quite some time, and then produces a list of 79 functions and variables. Scanning down the list, the only function that looks as if it might do the job is @code{insert-rectangle}. Indeed, this is the function we want; its documentation says: @smallexample @group insert-rectangle: Insert text of RECTANGLE with upper left corner at point. RECTANGLE's first line is inserted at point, its second line is inserted at a point vertically under point, etc. RECTANGLE should be a list of strings. @end group @end smallexample We can run a quick test, to make sure it does what we expect of it. Here is the result of placing the cursor after the @code{insert-rectangle} expression and typing @kbd{C-u C-x C-e} (@code{eval-last-sexp}). The function inserts the strings @samp{"first"}, @samp{"second"}, and @samp{"third"} at and below point. Also the function returns @code{nil}. @example @group (insert-rectangle '("first" "second" "third"))first second third nil @end group @end example @noindent Of course, we won't be inserting the text of the @code{insert-rectangle} expression itself into the buffer in which we are making the graph, but will call the function from our program. We shall, however, have to make sure that point is in the buffer at the place where the @code{insert-rectangle} function will insert its column of strings. If you are reading this in Info, you can see how this works by switching to another buffer, such as the @file{*scratch*} buffer, placing point somewhere in the buffer, typing @kbd{M-@key{ESC}}, typing the @code{insert-rectangle} expression into the minibuffer at the prompt, and then typing @key{RET}. This causes Emacs to evaluate the expression in the minibuffer, but to use as the value of point the position of point in the @file{*scratch*} buffer. (@kbd{M-@key{ESC}} is the keybinding for @code{eval-expression}.) We find when we do this that point ends up at the end of the last inserted line---that is to say, this function moves point as a side-effect. If we were to repeat the command, with point at this position, the next insertion would be below and to the right of the previous insertion. We don't want this! If we are going to make a bar graph, the columns need to be beside each other. So we discover that each cycle of the column-inserting @code{while} loop must reposition point to the place we want it, and that place will be at the top, not the bottom, of the column. Moreover, we remember that when we print a graph, we do not expect all the columns to be the same height. This means that the top of each column may be at a different height from the previous one. We cannot simply reposition point to the same line each time, but moved over to the right---or perhaps we can@dots{} We are planning to make the columns of the bar graph out of asterisks. The number of asterisks in the column is the number specified by the current element of the @code{numbers-list}. We need to construct a list of asterisks of the right length for each call to @code{insert-rectangle}. If this list consists solely of the requisit number of asterisks, then we will have position point the right number of lines above the base for the graph to print correctly. This could be difficult. Alternatively, if we can figure out some way to pass @code{insert-rectangle} a list of the same length each time, then we can place point on the same line each time, but move it over one column to the right for each new column. If we do this, however, some of the entries in the list passed to @code{insert-rectangle} must be blanks rather than asterisks. For example, if the maximum height of the graph is 5, but the height of the column is 3, then @code{insert-rectangle} requires an argument that looks like this: @example (" " " " "*" "*" "*") @end example This last proposal is not so difficult, so long as we can determine the column height. There are two ways for us to specify the column height: we can arbitrarily state what it will be, which would work fine for graphs of that height; or we can search through the list of numbers and use the maximum height of the list as the maximum height of the graph. If the latter operation were difficult, then the former procedure would be easiest, but there is a function built into Emacs that determines the maximum of its arguments. We can use that function. The function is called @code{max} and it returns the largest of all its arguments, which must be numbers. Thus, for example, @example (max 3 4 6 5 7 3) @end example @noindent returns 7. (A corresponding function called @code{min} returns the smallest of all its arguments.) @findex max @findex min However, we cannot simply call @code{max} on the @code{numbers-list}; the @code{max} function expects numbers as its argument, not a list of numbers. Thus, the following expression, @example (max '(3 4 6 5 7 3)) @end example @noindent produces the following error message; @example Wrong type of argument: integer-or-marker-p, (3 4 6 5 7 3) @end example @findex apply We need a function that passes a list of arguments to a function. This function is @code{apply}. This function `applies' its first argument (a function) to its remaining arguments, the last of which may be a list. @need 1250 For example, @example (apply 'max 3 4 7 3 '(4 8 5)) @end example @noindent returns 8. (Incidentally, I don't know how you would learn of this function without a book such as this. It is possible to discover other functions, like @code{search-forward} or @code{insert-rectangle}, by guessing at a part of their names and then using @code{apropos}. Even though its base in metaphor is clear---`apply' its first argument to the rest---I doubt a novice would come up with that particular word when using @code{apropos} or other aid. Of course, I could be wrong; after all, the function was first named by someone who had to invent it.) The second and subsequent arguments to @code{apply} are optional, so we can use @code{apply} to call a function and pass the elements of a list to it, like this, which also returns 8: @example (apply 'max '(4 8 5)) @end example This latter way is how we will use @code{apply}. The @code{recursive-lengths-list-many-files} function returns a numbers' list to which we can apply @code{max} (we could also apply @code{max} to the sorted numbers' list; it does not matter whether the list is sorted or not.) Hence, the operation for finding the maximum height of the graph is this: @example (setq max-graph-height (apply 'max numbers-list)) @end example Now we can return to the question of how to create a list of strings for a column of the graph. Told the maximum height of the graph and the number of asterisks that should appear in the column, the function should return a list of strings for the @code{insert-rectangle} command to insert. Each column is made up of asterisks or blanks. Since the function is passed the value of the height of the column and the number of asterisks in the column, the number of blanks can be found by subtracting the number of asterisks from the height of the column. Given the number of blanks and the number of asterisks, two @code{while} loops can be used to construct the list: @example @group ;;; @r{First version.} (defun column-of-graph (max-graph-height actual-height) "Return list of strings that is one column of a graph." (let ((insert-list nil) (number-of-top-blanks (- max-graph-height actual-height))) @end group @group ;; @r{Fill in asterisks.} (while (> actual-height 0) (setq insert-list (cons "*" insert-list)) (setq actual-height (1- actual-height))) @end group @group ;; @r{Fill in blanks.} (while (> number-of-top-blanks 0) (setq insert-list (cons " " insert-list)) (setq number-of-top-blanks (1- number-of-top-blanks))) @end group @group ;; @r{Return whole list.} insert-list)) @end group @end example If you install this function and then evaluate the following expression you will see that it returns the list as desired: @example (column-of-graph 5 3) @end example @noindent returns @example (" " " " "*" "*" "*") @end example As written, @code{column-of-graph} contains a major flaw: the symbols used for the blank and for the marked entries in the column are `hard-coded' as a space and asterisk. This is fine for a prototype, but you, or another user, may wish to use other symbols. For example, in testing the graph function, you many want to use a period in place of the space, to make sure the point is being repositioned properly each time the @code{insert-rectangle} function is called; or you might want to substitute a @samp{+} sign or other symbol for the asterisk. You might even want to make a graph-column that is more than one display column wide. The program should be more flexible. The way to do that is to replace the blank and the asterisk with two variables that we can call @code{graph-blank} and @code{graph-symbol} and define those variables separately. Also, the documentation is not well written. These considerations lead us to the second version of the function: @example @group (defvar graph-symbol "*" "String used as symbol in graph, usually an asterisk.") @end group @group (defvar graph-blank " " "String used as blank in graph, usually a blank space. graph-blank must be the same number of columns wide as graph-symbol.") @end group @end example @noindent (For an explanation of @code{defvar}, see @ref{defvar, , Initializing a Variable with @code{defvar}}.) @example @group ;;; @r{Second version.} (defun column-of-graph (max-graph-height actual-height) "Return list of MAX-GRAPH-HEIGHT strings; ACTUAL-HEIGHT are graph-symbols. @end group @group The graph-symbols are contiguous entries at the end of the list. The list will be inserted as one column of a graph. The strings are either graph-blank or graph-symbol." @end group @group (let ((insert-list nil) (number-of-top-blanks (- max-graph-height actual-height))) @end group @group ;; @r{Fill in @code{graph-symbols}.} (while (> actual-height 0) (setq insert-list (cons graph-symbol insert-list)) (setq actual-height (1- actual-height))) @end group @group ;; @r{Fill in @code{graph-blanks}.} (while (> number-of-top-blanks 0) (setq insert-list (cons graph-blank insert-list)) (setq number-of-top-blanks (1- number-of-top-blanks))) ;; @r{Return whole list.} insert-list)) @end group @end example If we wished, we could rewrite @code{column-of-graph} a third time to provide optionally for a line graph as well as for a bar graph. This would not be hard to do. One way to think of a line graph is that it is no more than a bar graph in which the part of each bar that is below the top is blank. To construct a column for a line graph, the function first constructs a list of blanks that is one shorter than the value, then it uses @code{cons} to attach a graph symbol to the list; then it uses @code{cons} again to attach the `top blanks' to the list. It is easy to see how to write such a function, but since we don't need it, we will not do it. But the job could be done, and if it were done, it would be done with @code{column-of-graph}. Even more important, it is worth noting that few changes would have to be made anywhere else. The enhancement, if we ever wish to make it, is simple. Now, finally, we come to our first actual graph printing function. This prints the body of a graph, not the labels for the vertical and horizontal axes, so we can call this @code{graph-body-print}. @node graph-body-print, recursive-graph-body-print, Columns of a graph, Readying a Graph @section The @code{graph-body-print} Function @findex graph-body-print After our preparation in the preceding section, the @code{graph-body-print} function is straightforward. The function will print column after column of asterisks and blanks, using the elements of a numbers' list to specify the number of asterisks in each column. This is a repetitive act, which means we can use a decrementing @code{while} loop or recursive function for the job. In this section, we will write the definition using a @code{while} loop. The @code{column-of-graph} function requires the height of the graph as an argument, so we should determine and record that as a local variable. This leads us to the following template for the @code{while} loop version of this function: @example @group (defun graph-body-print (numbers-list) "@var{documentation}@dots{}" (let ((height @dots{} @dots{})) @end group @group (while numbers-list @var{insert-columns-and-reposition-point} (setq numbers-list (cdr numbers-list))))) @end group @end example @noindent We need to fill in the slots of the template. Clearly, we can use the @code{(apply 'max numbers-list)} expression to determine the height of the graph. The @code{while} loop will cycle through the @code{numbers-list} one element at a time. As it is shortened by the @code{(setq numbers-list (cdr numbers-list))} expression, the @sc{car} of each instance of the list is the value of the argument for @code{column-of-graph}. At each cycle of the @code{while} loop, the @code{insert-rectangle} function inserts the list returned by @code{column-of-graph}. Since the @code{insert-rectangle} function moves point to the lower right of the inserted rectangle, we need to save the location of point at the time the rectangle is inserted, move back to that position after the rectangle is inserted, and then move horizontally to the next place from which @code{insert-rectangle} is called. If the inserted columns are one character wide, as they will be if single blanks and asterisks are used, the repositioning command is simply @code{(forward-char 1)}; however, the width of a column may be greater than one. This means that the repositioning command should be written @code{(forward-char symbol-width)}. The @code{symbol-width} itself is the length of a @code{graph-blank} and can be found using the expression @code{(length graph-blank)}. The best place to bind the @code{symbol-width} variable to the value of the width of graph column is in the varlist of the @code{let} expression. @need 1250 These considerations lead to the following function definition: @example @group (defun graph-body-print (numbers-list) "Print a bar graph of the NUMBERS-LIST. The numbers-list consists of the Y-axis values." (let ((height (apply 'max numbers-list)) (symbol-width (length graph-blank)) from-position) @end group @group (while numbers-list (setq from-position (point)) (insert-rectangle (column-of-graph height (car numbers-list))) (goto-char from-position) (forward-char symbol-width) @end group @group ;; @r{Draw graph column by column.} (sit-for 0) (setq numbers-list (cdr numbers-list))) @end group @group ;; @r{Place point for X axis labels.} (forward-line height) (insert "\n") )) @end group @end example @noindent The one unexpected expression in this function is the @w{@code{(sit-for 0)}} expression in the @code{while} loop. This expression makes the graph printing operation more interesting to watch than it would be otherwise. The expression causes Emacs to `sit' or do nothing for a zero length of time and then redraw the screen. Placed here, it causes Emacs to redraw the screen column by column. Without it, Emacs would not redraw the screen until the function exits. We can test @code{graph-body-print} with a short list of numbers. @enumerate @item Install @code{graph-symbol}, @code{graph-blank}, @code{column-of-graph} and @code{graph-body-print}. @item Copy the following expression: @example (graph-body-print '(1 2 3 4 6 4 3 5 7 6 5 2 3)) @end example @item Switch to the @file{*scratch*} buffer and place the cursor where you want the graph to start. @item Type @kbd{M-@key{ESC}} (@code{eval-expression}). @item Yank the @code{graph-body-print} expression into the minibuffer with @kbd{C-y} (@code{yank)}. @item Press @key{RET} to evaluate the @code{graph-body-print} expression. @end enumerate Emacs will print a graph like this: @example @group * * ** * **** *** **** ********* * ************ ************* @end group @end example @node recursive-graph-body-print, Printed Axes, graph-body-print, Readying a Graph @section The @code{recursive-graph-body-print} Function @findex recursive-graph-body-print The @code{graph-body-print} function may also be written recursively. In this case, it is divided into two parts: an outside `wrapper' that uses a @code{let} expression to determine the values of several variables that need only be found once, such as the maximum height of the graph, and a inside function that is called recursively to print the graph. @need 1250 The `wrapper' is uncomplicated: @example @group (defun recursive-graph-body-print (numbers-list) "Print a bar graph of the NUMBERS-LIST. The numbers-list consists of the Y-axis values." (let ((height (apply 'max numbers-list)) (symbol-width (length graph-blank)) from-position) (recursive-graph-body-print-internal numbers-list height symbol-width))) @end group @end example The recursive function is a little more difficult. It has four parts: the `do-again-test', the printing code, the recursive call, and the `next-step-expression'. The `do-again-test' is an @code{if} expression that determines whether the @code{numbers-list} contains any remaining elements; if it does, the function prints one column of the graph using the printing code and calls itself again. The function calls itself again according to the value produced by the `next-step-expression' which causes the call to act on a shorter version of the @code{numbers-list}. @example @group (defun recursive-graph-body-print-internal (numbers-list height symbol-width) "Print a bar graph. Used within recursive-graph-body-print function." @end group @group (if numbers-list (progn (setq from-position (point)) (insert-rectangle (column-of-graph height (car numbers-list))) @end group @group (goto-char from-position) (forward-char symbol-width) (sit-for 0) ; @r{Draw graph column by column.} (recursive-graph-body-print-internal (cdr numbers-list) height symbol-width)))) @end group @end example @need 1250 After installation, this expression can be tested; here is a sample: @example (recursive-graph-body-print '(3 2 5 6 7 5 3 4 6 4 3 2 1)) @end example Here is what @code{recursive-graph-body-print} produces: @example @group * ** * **** * **** *** * ********* ************ ************* @end group @end example Either of these two functions, @code{graph-body-print} or @code{recursive-graph-body-print}, create the body of a graph. @node Printed Axes, Line Graph Exercise, recursive-graph-body-print, Readying a Graph @section Need for Printed Axes A graph needs printed axes, so you can orient yourself. For a do-once project, it may be reasonable to draw the axes by hand using Emacs's Picture mode; but a graph drawing function may be used more than once. For this reason, I have written enhancements to the basic @code{print-graph-body} function that automatically print labels for the horizontal and vertical axes. Since the label printing functions do not contain much new material, I have placed their description in an appendix. @xref{Full Graph, , A Graph with Labelled Axes}. @node Line Graph Exercise, , Printed Axes, Readying a Graph @section Exercise Write a line graph version of the graph printing functions. @node Emacs Initialization, Debugging, Readying a Graph, Top @chapter Your @file{.emacs} File @cindex @file{.emacs} file @cindex Customizing your @file{.emacs} file @cindex Initialization file ``You don't have to like Emacs to like it'' -- this seemingly paradoxical statement is the secret of GNU Emacs. The plain, `out of the box' Emacs is a generic tool. Most people who use it, customize it to suit themselves. GNU Emacs is mostly written in Emacs Lisp; this means that by writing expressions in Emacs Lisp you can change or extend Emacs. @menu * Default Configuration:: Emacs has sensible defaults. * Site-wide Init:: You can write site-wide init files. * edit-options:: How to set some variables for a session. * Beginning a .emacs File:: How to write a @code{.emacs file}. * Text and Auto-fill:: Automatically wrap lines. * Mail Aliases:: Use abbreviations for email addresses. * Indent Tabs Mode:: Don't use tabs with @TeX{} * Keybindings:: Create some personal keybindings. * Loading Files:: Load (i.e.@: evaluate) files automatically. * Autoload:: Make functions available. * Simple Extension:: Define a function; bind it to a key. * Keymaps:: More about key binding. * X11 Colors:: Colors in version 19 in X. * V19 Miscellaneous:: Automatically resize minibuffer, and more. * Mode Line:: How to customize your mode line. @end menu @node Default Configuration, Site-wide Init, Emacs Initialization, Emacs Initialization @ifinfo @heading Emacs's Default Configuration @end ifinfo There are those who appreciate Emacs's default configuration. After all, Emacs starts you in C mode when you edit a C file, starts you in Fortran mode when you edit a Fortran file, and starts you in Fundamental mode when you edit an unadorned file. This all makes sense, if you do not know who is going to use Emacs. Who knows what a person hopes to do with an unadorned file? Fundamental mode is the right default for such a file, just as C mode is the right default for editing C code. But when you do know who is going to use Emacs---you, yourself---then it makes sense to customize Emacs. For example, I seldom want Fundamental mode when I edit an otherwise undistinguished file; I want Text mode. This is why I customize Emacs: so it suits me. You can customize and extend Emacs by writing or adapting a @file{~/.emacs} file. This is your personal initialization file; its contents, written in Emacs Lisp, tell Emacs what to do. This chapter describes a simple @file{.emacs} file; for more information, see @ref{Init File, , The Init File, emacs, The GNU Emacs Manual}, and @ref{Init File, , The Init File, elisp, The GNU Emacs Lisp Reference Manual}. @node Site-wide Init, edit-options, Default Configuration, Emacs Initialization @section Site-wide Initialization Files @cindex @file{default.el} init file @cindex @file{site-init.el} init file @cindex @file{site-load.el} init file In addition to your personal initialization file, Emacs automatically loads various site-wide initialization files, if they exist. These have the same form as your @file{.emacs} file, but are loaded by everyone. Two site-wide initialization files, @file{site-load.el} and @file{site-init.el}, are loaded into Emacs and then `dumped' if a `dumped' version of Emacs is created, as is most common. (Dumped copies of Emacs load more quickly. However, once a file is loaded and dumped, a change to it does not lead to a change in Emacs unless you load it yourself or re-dump Emacs. @xref{Building Emacs, , Building Emacs, elisp, The GNU Emacs Lisp Reference Manual}, and the @file{INSTALL} file.) Three other site-wide initialization files are loaded automatically each time you start Emacs, if they exist. These are @file{site-start.el}, which is loaded @emph{before} your @file{.emacs} file, and @file{default.el}, and the terminal type file, which are both loaded @emph{after} your @file{.emacs} file. Settings and definitions in your @file{.emacs} file will overwrite conflicting settings and definitions in a @file{site-start.el} file, if it exists; but the settings and definitions in a @file{default.el} or terminal type file will overwrite those in your @file{.emacs} file. (You can prevent interference from a terminal type file by setting @code{term-file-prefix} to @code{nil}. @xref{Simple Extension, , A Simple Extension}.) @c Rewritten to avoid overfull hbox. The @file{INSTALL} file that comes in the distribution contains descriptions of the @file{site-init.el} and @file{site-load.el} files. The @file{loadup.el}, @file{startup.el}, and @file{loaddefs.el} files control loading. These files are in the @file{lisp} directory of the Emacs distribution and are worth perusing. The @file{loaddefs.el} file contains a good many suggestions as to what to put into your own @file{.emacs} file, or into a site-wide initialization file. @node edit-options, Beginning a .emacs File, Site-wide Init, Emacs Initialization @section Setting Variables for One Session @findex edit-options @findex list-options @cindex Options, easily settable My copy of Emacs version 19.23 has 392 options that you can set with the @code{edit-options} command. These `options' are no more than variables such as we have seen earlier and defined using @code{defvar}. Emacs determines whether a variable is intended to be easily settable by looking at the first character in its documentation string; if the first character is an asterisk, @samp{*}, the variable is a user-settable option. (@xref{defvar, , Initializing a Variable with @code{defvar}}.) The @code{edit-options} command lists all the variables in Emacs that the people who wrote the Emacs Lisp libraries think ought to be readily settable. It provides an easy-to-use interface for resetting these variables. On the other hand, options set using @code{edit-options} are set only for the duration of your editing session. The new values are not saved between sessions. Each time Emacs starts, it reads the original @code{defvar} value in its source code. To carry a changed setting from one session to the next, you need to use a @code{setq} expression within a @file{.emacs} file or other file that you load every time you start a session. For me, the major use of the @code{edit-options} command is to suggest variables I might want to set in my @file{.emacs} file. I urge you to look through the list. @xref{Edit Options, , Editing Variable Values, emacs, The GNU Emacs Manual}, for more information. @node Beginning a .emacs File, Text and Auto-fill, edit-options, Emacs Initialization @section Beginning a @file{.emacs} File @cindex @file{.emacs} file, beginning of When you start Emacs, it loads your @file{.emacs} file unless you tell it not to by specifying @samp{-q} on the command line. (The @code{emacs -q} command gives you a plain, out-of-the-box Emacs.) A @file{.emacs} file contains Lisp expressions. Often, these are no more than expressions to set values; sometimes they are function definitions. @xref{Init File, , The Init File @file{~/.emacs}, emacs, The GNU Emacs Manual}, for a short description of initialization files. This chapter goes over some of the same ground, but is a walk among extracts from a complete, long-used @file{.emacs} file---my own. The first part of the file consists of comments: reminders to myself. By now, of course, I remember these things, but when I started, I did not. @example @group ;;;; Bob's .emacs file ; Robert J. Chassell ; 26 September 1985 @end group @end example @noindent Look at that date! I started this file a long time ago. I have been adding to it ever since. @example @group ; Each section in this file is introduced by a ; line beginning with four semicolons; and each ; entry is introduced by a line beginning with ; three semicolons. @end group @end example @noindent This describes the usual conventions for comments in Emacs Lisp. Everything on a line that follows a semicolon is a comment. Two, three, and four semicolons are used as section and subsection markers. (@xref{Comments, ,, elisp, The GNU Emacs Lisp Reference Manual}, for more about comments.) @example @group ;;;; The Help Key ; Control-h is the help key; ; after typing control-h, type a letter to ; indicate the subject about which you want help. ; For an explanation of the help facility, ; type control-h three times in a row. @end group @end example @noindent Just remember: type @kbd{C-h} three times for help. @example @group ; To find out about any mode, type control-h m ; while in that mode. For example, to find out ; about mail mode, enter mail mode and then type ; control-h m. @end group @end example @noindent `Mode help', as I call this, is very helpful. Usually, it tells you all you need to know. Of course, you don't need to include comments like these in your @file{.emacs} file. I included them in mine because I kept forgetting about Mode help or the conventions for comments---but I was able to remember to look here to remind myself. @node Text and Auto-fill, Mail Aliases, Beginning a .emacs File, Emacs Initialization @section Text and Auto Fill Mode Now we come to the part that `turns on' Text mode and Auto Fill mode. @example @group ;;; Text mode and Auto Fill mode ; The next two lines put Emacs into Text mode ; and Auto Fill mode, and are for writers who ; want to start writing prose rather than code. (setq default-major-mode 'text-mode) (add-hook 'text-mode-hook 'turn-on-auto-fill) @end group @end example Here is the first part of this @file{.emacs} file that does something besides remind a forgetful human! The first of the two lines in parentheses tells Emacs to turn on Text mode when you find a file, @emph{unless} that file should go into some other mode, such as C mode. @cindex Per-buffer, local variables list @cindex Local variables list, per-buffer, @cindex Automatic mode selection @cindex Mode selection, automatic When Emacs reads a file, it looks at the extension to the file name, if any. (The extension is the part that comes after a @samp{.}.) If the file ends with a @samp{.c} or @samp{.h} extension then Emacs turns on C mode. Also, Emacs looks at first nonblank line of the file; if the line says @w{@samp{-*- C -*-}}, Emacs turns on C mode. Emacs possesses a list of extensions and specifications that it uses automatically. In addition, Emacs looks near the last page for a per-buffer, ``local variables list'', if any. @ifinfo @xref{Choosing Modes, , How Major Modes are Chosen, emacs, The GNU Emacs Manual}. @xref{File Variables, , Local Variables in Files, emacs, The GNU Emacs Manual}. @end ifinfo @iftex See sections ``How Major Modes are Chosen'' and ``Local Variables in Files'' in @cite{The GNU Emacs Manual}, for information. @end iftex Now, back to the @file{.emacs} file. Here is the line again; how does it work? @cindex Text Mode turned on @example (setq default-major-mode 'text-mode) @end example @noindent This line is a short, but complete Emacs Lisp expression. We are already familiar with @code{setq}. It sets the following variable, @code{default-major-mode}, to the subsequent value, which is @code{text-mode}. The single quote mark before @code{text-mode} tells Emacs to deal directly with the @code{text-mode} variable, not with whatever it might stand for. @xref{set & setq, , Setting the Value of a Variable}, for a reminder of how @code{setq} works. The main point is that there is no difference between the procedure you use to set a value in your @file{.emacs} file and the procedure you use anywhere else in Emacs. Here is the second line: @cindex Auto Fill mode turned on @findex add-hook @example (add-hook 'text-mode-hook 'turn-on-auto-fill) @end example @noindent In this line, the @code{add-hook} command, adds @code{turn-on-auto-fill} to the variable called @code{text-mode-hook}. @code{turn-on-auto-fill} is the name of a program, that, you guessed it!, turns on Auto Fill mode. Every time Emacs turns on Text mode, Emacs runs the commands `hooked' onto Text mode. So every time Emacs turns on Text mode, Emacs also turns on Auto Fill mode. In brief, the first line causes Emacs to enter Text mode when you edit a file, unless the file name extension, first non-blank line, or local variables tell Emacs otherwise. Text mode among other actions, sets the syntax table to work conveniently for writers. In Text mode, Emacs considers an apostrophe as part of a word like a letter; but Emacs does not consider a period or a space as part of a word. Thus, @kbd{M-f} moves you over @samp{it's}. On the other hand, in C mode, @kbd{M-f} stops just after the @samp{t} of @samp{it's}. The second line causes Emacs to turn on Auto Fill mode when it turns on Text mode. In Auto Fill mode, Emacs automatically breaks a line that is too wide and brings the excessively wide part of the line down to the next line. Emacs breaks lines between words, not within them. When Auto Fill mode is turned off, lines continue to the right as you type them. Depending on how you set the value of @code{truncate-lines}, the words you type either disappear off the right side of the screen, or else are shown, in a rather ugly and unreadable manner, as a continuation line on the screen. @node Mail Aliases, Indent Tabs Mode, Text and Auto-fill, Emacs Initialization @section Mail Aliases Here is a @code{setq} to `turn on' mail aliases, along with more reminders. @example @group ;;; Mail mode ; To enter mail mode, type `C-x m' ; To enter RMAIL (for reading mail), ; type `M-x rmail' (setq mail-aliases t) @end group @end example @cindex Mail aliases @noindent This @code{setq} command sets the value of the variable @code{mail-aliases} to @code{t}. Since @code{t} means true, the line says, in effect, ``Yes, use mail aliases.'' Mail aliases are convenient short names for long email addresses or for lists of email addresses. The file where you keep your `aliases' is @file{~/.mailrc}. You write an alias like this: @example alias geo george@@foobar.wiz.edu @end example @noindent When you write a message to George, address it to @samp{geo}; the mailer will automatically expand @samp{geo} to the full address. @node Indent Tabs Mode, Keybindings, Mail Aliases, Emacs Initialization @section Indent Tabs Mode @cindex Tabs, preventing @findex indent-tabs-mode By default, Emacs inserts tabs in place of multiple spaces when it formats a region. (For example, you might indent many lines of text all at once with the @code{indent-region} command.) Tabs look fine on a terminal or with ordinary printing, but they produce badly indented output when you use @TeX{} or Texinfo since @TeX{} ignores tabs. @need 1250 The following turns off Indent Tabs mode: @example @group ;;; Prevent Extraneous Tabs (setq-default indent-tabs-mode nil) @end group @end example Note that this line uses @code{setq-default} rather than the @code{setq} command that we have see before. The @code{setq-default} command sets values only in buffers that do not have their own local values for the variable. @ifinfo @xref{Just Spaces, , Tabs vs. Spaces, emacs, The GNU Emacs Manual}. @xref{File Variables, , Local Variables in Files, emacs, The GNU Emacs Manual}. @end ifinfo @iftex See sections ``Tabs vs.@: Spaces'' and ``Local Variables in Files'' in @cite{The GNU Emacs Manual}. @end iftex @node Keybindings, Loading Files, Indent Tabs Mode, Emacs Initialization @section Some Keybindings Now for some personal keybindings: @example @group ;;; Compare windows (global-set-key "\C-cw" 'compare-windows) @end group @end example @findex compare-windows @code{compare-windows} is a nifty command that compares the text in your current window with text in the next window. It makes the comparison by starting at point in each window, moving over text in each window as far as they match. I use this command all the time. This also shows how to set a key globally, for all modes. @cindex Setting a key globally @cindex Global set key @cindex Key setting globally @findex global-set-key The command is @code{global-set-key}. It is followed by the keybinding. In a @file{.emacs} file, the keybinding is written as shown: @code{\C-c} stands for `control-c', which means `press the control key and the @kbd{c} key at the same time'. The @code{w} means `press the @kbd{w} key'. The keybinding is surrounded by double quotation marks. In documentation, you would write this as @kbd{C-c w}. (If you were binding a @key{META} key, such as @kbd{M-c}, rather than a @key{CTL} key, you would write @code{\M-c}. @xref{Init Rebinding, , Rebinding Keys in Your Init File, emacs, The GNU Emacs Manual}, for details.) The command invoked by the keys is @code{compare-windows}. Note that @code{compare-windows} is preceded by a single quote; otherwise, Emacs would first try to evaluate the symbol to determine its value. These three things, the double quotation marks, the backslash before the @samp{C}, and the single quote mark are necessary parts of keybinding that I tend to forget. Fortunately, I have come to remember that I should look at my existing @file{.emacs} file, and adapt what is there. As for the keybinding itself: @kbd{C-c w}. This combines the prefix key, @kbd{C-c}, with a single character, in this case, @kbd{w}. This set of keys, @kbd{C-c} followed by a single character, is strictly reserved for individuals' own use. If you ever write an extension to Emacs, please avoid taking any of these keys for public use. Create a key like @kbd{C-c C-w} instead. Otherwise, we will run out of `own' keys. @need 1250 Here is another keybinding, with a comment: @example @group ;;; Keybinding for `occur' ; I use occur a lot, so let's bind it to a key: (global-set-key "\C-co" 'occur) @end group @end example @findex occur The @code{occur} command shows all the lines in the current buffer that contain a match for a regular expression. Matching lines are shown in a buffer called @file{*Occur*}. That buffer serves as a menu to jump to occurrences. @findex global-unset-key @cindex Unbinding key @cindex Key unbinding @need 1250 Here is how to unbind a key, so it does not work: @example @group ;;; Unbind `C-x f' (global-unset-key "\C-xf") @end group @end example There is a reason for this unbinding: I found I inadvertently typed @w{@kbd{C-x f}} when I meant to type @kbd{C-x C-f}. Rather than find a file, as I intended, I accidentally set the width for filled text, almost always to a width I did not want. Since I hardly ever reset my default width, I simply unbound the key. @findex list-buffers, @r{rebound} @findex buffer-menu, @r{bound to key} @need 1250 The following rebinds an existing key: @example @group ;;; Rebind `C-x C-b' for `buffer-menu' (global-set-key "\C-x\C-b" 'buffer-menu) @end group @end example By default, @kbd{C-x C-b} runs the @code{list-buffers} command. This command lists your buffers in @emph{another} window. Since I almost always want to do something in that window, I prefer the @code{buffer-menu} command, which not only lists the buffers, but moves point into that window. @node Loading Files, Autoload, Keybindings, Emacs Initialization @section Loading Files @cindex Loading files @c findex load Many people in the GNU Emacs community have written extensions to Emacs. As time goes by, these extensions are often included in new releases. For example, the Calendar and Diary packages are now part of the standard Emacs version 19 distribution; they were not part of the standard Emacs version 18 distribution. (Calc, which I consider a vital part of Emacs, would be part of the standard distribution except that it is so large it is packaged separately.) You can use a @code{load} command to evaluate a complete file and thereby install all the functions and variables in the file into Emacs. For example: @example (load "~/emacs/kfill") @end example This evaluates, i.e.@: loads, the @file{kfill.el} file (or if it exists, the faster, byte compiled @file{kfill.elc} file) from the @file{emacs} sub-directory of your home directory. (@file{kfill.el} was adapted from Kyle E.@: Jones' @file{filladapt.el} package by Bob Weiner and ``provides no muss, no fuss word wrapping and filling of paragraphs with hanging indents, included text from news and mail messages, and Lisp, C++, PostScript or shell comments.'' I use it all the time and hope it is incorporated into the standard distribution.) @vindex load-path If you load many extensions, as I do, then instead of specifying the exact location of the extension file, as shown above, you can specify that directory as part of Emacs's @code{load-path}. Then, when Emacs loads a file, it will search that directory as well as its default list of directories. (The default list is specified in @file{paths.h} when Emacs is built.) @need 1250 The following command adds your @file{~/emacs} directory to the existing load path: @example @group ;;; Emacs Load Path (setq load-path (cons "~/emacs" load-path)) @end group @end example Incidentally, @code{load-library} is an interactive interface to the @code{load} function. The complete function looks like this: @findex load-library @example @group (defun load-library (library) "Load the library named LIBRARY. This is an interface to the function `load'." (interactive "sLoad library: ") (load library)) @end group @end example The name of the function, @code{load-library}, comes from the use of `library' as a conventional synonym for `file'. The source for the @code{load-library} command is in the @file{files.el} library. Another interactive command that does a slightly different job is @code{load-file}. @xref{Lisp Libraries, , Libraries of Lisp Code for Emacs, emacs, The GNU Emacs Manual}, for information on the distinction between @code{load-library} and this command. @node Autoload, Simple Extension, Loading Files, Emacs Initialization @section Autoloading @findex autoload Instead of installing a function by loading the file that contains it, or by evaluating the function definition, you can make the function available but not actually install it until it is first called. This is called @dfn{autoloading}. When you execute an autoloaded function, Emacs automatically evaluates the file that contains the definition, and then calls the function. Emacs starts quicker with autoloaded functions, since their libraries are not loaded right away; but you need to wait a moment when you first use such a function, while its containing file is evaluated. Rarely used functions are frequently autoloaded. The @file{loaddefs.el} library contains hundreds of autoloaded functions, from @code{bookmark-set} to @code{wordstar-mode}. Of course, you may come to use a `rare' function frequently. In this case, you should load that function's file with a @code{load} expression in your @file{.emacs} file. In my @file{.emacs} file for Emacs version 19.23, I load 17 libraries that contain functions that would otherwise be autoloaded. (Actually, it would have been better to include these files in my `dumped' Emacs when I built it, but I forgot. @xref{Building Emacs, , Building Emacs, elisp, The GNU Emacs Lisp Reference Manual}, and the @file{INSTALL} file for more about dumping.) You may also want to include autoloaded expressions in your @file{.emacs} file. @code{autoload} is a built-in function that takes up to five arguments, the final three of which are optional. The first argument is the name of the function to be autoloaded; the second is the name of the file to be loaded. The third argument is documentation for the function, and the fourth tells whether the function can be called interactively. The fifth argument tells what type of object---@code{autoload} can handle a keymap or macro as well as a function (the default is a function). Here is a typical example: @example @group (autoload 'html-helper-mode "html-helper-mode" "Edit HTML documents" t) @end group @end example @c Kludge to reduce overfull hbox. (Ignore small hbox in largebook) @ifclear largebook @noindent This expression autoloads the @code{html-helper-mode} function. It takes it from the @file{html-helper-mode.el} file (or, if it exists, from the byte compiled file @file{html-helper-mode.elc}.) The file must be located in a directory specified by @code{load-path}. The documentation says that this is a mode to help you edit documents written in the HyperText Markup Language. You can call this mode interactively by typing @kbd{M-x html-helper-mode}. (You need to duplicate the function's regular documentation in the autoload expression because the regular function is not yet loaded, so its documentation is not available.) @end ifclear @ifset largebook @noindent This expression autoloads the @code{html-helper-mode} function from the @file{html-helper-mode.el} file (or, if it exists, from the byte compiled file @file{html-helper-mode.elc}.) The file must be located in a directory specified by @code{load-path}. The documentation says that this is a mode to help you edit documents written in the HyperText Markup Language. You can call this mode interactively by typing @kbd{M-x html-helper-mode}. (You need to duplicate the function's regular documentation in the autoload expression because the regular function is not yet loaded, so its documentation is not available.) @end ifset @xref{Autoload, , Autoload, elisp, The GNU Emacs Lisp Reference Manual}, for more information. @node Simple Extension, Keymaps, Autoload, Emacs Initialization @section A Simple Extension: @code{line-to-top-of-window} @findex line-to-top-of-window @cindex Simple extension in @file{.emacs} file Here is a simple extension to Emacs that moves the line point is on to the top of the window. I use this all the time, to make text easier to read. You can put the following code into a separate file and then load it from your @file{.emacs} file, or you can include it within your @file{.emacs} file. @need 1250 Here is the definition: @example @group ;;; Line to top of window; ;;; replace three keystroke sequence C-u 0 C-l (defun line-to-top-of-window () "Move the line point is on to top of window." (interactive) (recenter 0)) @end group @end example @need 1250 Now for the keybinding. Although most of an Emacs version 18 @file{.emacs} file works with version 19, there are some differences (also, of course, there are new features in Emacs 19). In version 19 Emacs, you can write a function key like this: @samp{[f6]}. In version 18, you must specify the key strokes sent by the keyboard when you press that function key. For example, a Zenith 29 keyboard sends @key{ESC P} when I press its sixth function key; an Ann Arbor Ambassador keyboard sends @key{ESC O F}. Write these keystrokes as @samp{\eP} and @samp{\eOF}, respectively. In my version 18 @file{.emacs} file, I bind @code{line-to-top-of-window} to a key that depends on the type of terminal: @example @group (defun z29-key-bindings () "Function keybindings for Z29 terminal." ;; @dots{} (global-set-key "\eP" 'line-to-top-of-window)) @end group @group (defun aaa-key-bindings () "Function keybindings for Ann Arbor Ambassador" ;; @dots{} (global-set-key "\eOF" 'line-to-top-of-window)) @end group @end example @noindent (You can find out what a function key sends by typing the function key, and then typing @kbd{C-h l} (@code{view-lossage}) which displays the last 100 input keystrokes.) After specifying the key bindings, I evaluate an expression that chooses among keybindings, depending on the type of terminal I am using. However, before doing that, I turn off the predefined, default terminal-specific keybindings, which overwrite bindings in the @file{.emacs} if they clash. @example @group ;;; Turn Off Predefined Terminal Keybindings ; The following turns off the predefined ; terminal-specific keybindings such as the ; vt100 keybindings in lisp/term/vt100.el. ; If there are no predefined terminal ; keybindings, or if you like them, ; comment this out. (setq term-file-prefix nil) @end group @end example @need 1250 Here is the selection expression itself: @example @group (let ((term (getenv "TERM"))) (cond ((equal term "z29") (z29-key-bindings)) ((equal term "aaa") (aaa-key-bindings)) (t (message "No binding for terminal type %s." term)))) @end group @end example In Emacs version 19, function keys (as well as mouse button events and non-@sc{ascii} characters) are written within square brackets, without quotation marks. I bind @code{line-to-top-of-window} to my @key{F6} function key like this: @example (global-set-key [f6] 'line-to-top-of-window) @end example @noindent Much simpler! For more information, see @ref{Init Rebinding, , Rebinding Keys in Your Init File, emacs, The GNU Emacs Manual}. @cindex Conditional 'twixt Emacs 18 and 19 @cindex Version of Emacs, choosing @cindex Emacs version, choosing If you run both Emacs 18 and Emacs 19, you can select which code to evaluate with the following conditional: @example @group (if (string= (int-to-string 18) (substring (emacs-version) 10 12)) ;; evaluate version 18 code (progn @dots{} ) ;; else evaluate version 19 code @dots{} @end group @end example @node Keymaps, X11 Colors, Simple Extension, Emacs Initialization @section Keymaps @cindex Keymaps @cindex Rebinding keys Emacs uses @dfn{keymaps} to record which keys call which commands. Specific modes, such as C mode or Text mode, have their own keymaps; the mode-specific keymaps override the global map that is shared by all buffers. The @code{global-set-key} function binds, or rebinds, the global keymap. For example, the following binds the key @kbd{C-c C-l} to the function @code{line-to-top-of-window}: @example (global-set-key "\C-c\C-l" 'line-to-top-of-window)) @end example Mode-specific keymaps are bound using the @code{define-key} function, which takes a specific keymap as an argument, as well as the key and the command. For example, my @file{.emacs} file contains the following expression to bind the @code{texinfo-insert-@@group} command to @kbd{C-c C-c g}: @example @group (define-key texinfo-mode-map "\C-c\C-cg" 'texinfo-insert-@@group) @end group @end example @noindent The @code{texinfo-insert-@@group} function itself is a little extension to Texinfo mode that inserts @samp{@@group} into a Texinfo file. I use this command all the time and prefer to type the three strokes @kbd{C-c C-c g} rather than the six strokes @kbd{@@ g r o u p}. (@samp{@@group} and its matching @samp{@@end group} are commands that keep all enclosed text together on one page; many multi-line examples in this book are surrounded by @samp{@@group @dots{} @@end group}.) @need 1250 Here is the @code{texinfo-insert-@@group} function definition: @example @group (defun texinfo-insert-@@group () "Insert the string @@group in a Texinfo buffer." (interactive) (beginning-of-line) (insert "@@group\n")) @end group @end example (Of course, I could have used Abbrev mode to save typing, rather than write a function to insert a word; but I prefer key strokes consistent with other Texinfo mode key bindings.) You will see numerous @code{define-key} expressions in @file{loaddefs.el} as well as in the various mode libraries, such as @file{c-mode.el} and @file{lisp-mode.el}. @xref{Key Bindings, , Customizing Key Bindings, emacs, The GNU Emacs Manual}, and @ref{Keymaps, , Keymaps, elisp, The GNU Emacs Lisp Reference Manual}, for more information about keymaps. @node X11 Colors, V19 Miscellaneous, Keymaps, Emacs Initialization @section X11 Colors You can specify colors when you use Emacs version 19 with the MIT X Windowing system. (All the previous examples should work with both Emacs version 18 and Emacs version 19; this works only with Emacs version 19.) I hate the default colors and specify my own. Most of my specifications are in various X initialization files. I wrote notes to myself in my @file{.emacs} file to remind myself what I did: @example @group ;; I use TWM for window manager; ;; my ~/.xsession file specifies: ; xsetroot -solid navyblue -fg white @end group @end example @need 1250 @noindent Actually, the root of the X window is not part of Emacs at all, but I like the reminder anyhow. @example @group ;; My ~/.Xresources file specifies: ; XTerm*Background: sky blue ; XTerm*Foreground: white ; emacs*geometry: =80x40+100+0 @end group @group ; emacs*background: blue ; emacs*foreground: grey97 ; emacs*cursorColor: white ; emacs*pointerColor: white @end group @end example @need 1250 Here are the expressions in my @file{.emacs} file that set values: @example @group ;;; Set highlighting colors for isearch and drag (set-face-foreground 'highlight "white" ) (set-face-background 'highlight "slate blue") (set-face-background 'region "slate blue") (set-face-background 'secondary-selection "turquoise") @end group @group ;; Set calendar highlighting colors (setq calendar-load-hook '(lambda () (set-face-foreground 'diary-face "skyblue") (set-face-background 'holiday-face "slate blue") (set-face-foreground 'holiday-face "white"))) @end group @end example The various shades of blue soothe my eye and prevent me from seeing the screen flicker. @node V19 Miscellaneous, Mode Line, X11 Colors, Emacs Initialization @section V19 Miscellaneous Here are a few miscellaneous settings for version 19 Emacs: @sp 1 @itemize @minus @item Automatically resize the minibuffer as needed: @example @group (resize-minibuffer-mode 1) (setq resize-minibuffer-mode t) @end group @end example @item Turn on highlighting for search strings: @example (setq search-highlight t) @end example @item Set every frame to show a menu bar and to come forward when you move the mouse onto it. @example @group (setq default-frame-alist '((menu-bar-lines . 1) (auto-lower . t) (auto-raise . t))) @end group @end example @item Set the shape and color of the mouse cursor: @example @group ; Cursor shapes are defined in ; `/usr/include/X11/cursorfont.h'; ; for example, the `target' cursor is number 128; ; the `top_left_arrow' cursor is number 132. @end group @group (let ((mpointer (x-get-resource "*mpointer" "*emacs*mpointer"))) ;; If you have not set your mouse pointer ;; then sent it, otherwise leave as is: (if (eq mpointer nil) (setq mpointer "132")) ; top_left_arrow @end group @group (setq x-pointer-shape (string-to-int mpointer)) (set-mouse-color "white")) @end group @end example @end itemize @node Mode Line, , V19 Miscellaneous, Emacs Initialization @section A Modified Mode Line @vindex default-mode-line-format @cindex Mode line format Finally, a feature I really like: a modified mode line. Since I sometimes work over a network, I replaced the @samp{Emacs: } that is normally written on the left hand side of the mode line by the name of the system---otherwise, I forget which machine I am using. In addition, I list the default directory lest I lose track of where I am, and I specify the line point is on, with @samp{Line} spelled out. My @file{.emacs} file looks like this: @example @group (setq mode-line-system-identification (substring (system-name) 0 (string-match "\\..+" (system-name)))) @end group @group (setq default-mode-line-format (list "" 'mode-line-modified "<" 'mode-line-system-identification "> " "%14b" " " 'default-directory " " "%[(" 'mode-name 'minor-mode-alist "%n" 'mode-line-process ")%]--" "Line %l--" '(-3 . "%P") "-%-")) @end group @group ;; Start with new default. (setq mode-line-format default-mode-line-format) @end group @end example @noindent I set the @emph{default} mode line format so as to permit various modes, such as Info, to override it. Many elements in the list are self-explanatory: @code{mode-line-modified} is a variable the tells whether the buffer has been modified, @code{mode-name} tells the name of the mode, and so on. The @samp{"%14b"} displays the current buffer name (using the @code{buffer-name} function with which we are familiar); the `14' specifies the maximum number of characters that will be displayed. When a name has fewer characters, whitespace is added to fill out to this number. @samp{%[} and @samp{%]} cause a pair of square brackets to appear for each recursive editing level. @samp{%n} says `Narrow' when narrowing is in effect. @samp{%P} tells you the percentage of the buffer that is above the bottom of the window, or `Top', `Bottom', or `All'. (A lower case @samp{p} tell you the percentage above the @emph{top} of the window.) @samp{%-} inserts enough dashes to fill out the line. In and after Emacs version 19.29, you can use @code{frame-title-format} to set the title of an Emacs frame. This variable has the same structure as @code{mode-line-format}. Mode line formats are described in @ref{Mode Line Format, , Mode Line Format, elisp, The GNU Emacs Lisp Reference Manual}. Remember, ``You don't have to like Emacs to like it'' --- your own Emacs can have different colors, different commands, and different keys than a default Emacs. On the other hand, if you want to bring up a plain `out of the box' Emacs, with no customization, type: @example emacs -q @end example @noindent This will start an Emacs that does @emph{not} load your @file{~/.emacs} initialization file. A plain, default Emacs. Nothing more. @node Debugging, Conclusion, Emacs Initialization, Top @chapter Debugging @cindex debugging GNU Emacs has two debuggers, @code{debug} and @code{edebug}. The first is built into the internals of Emacs and is always with you; the second is an extension to Emacs that has become part of the standard distribution in version 19. Both debuggers are described extensively in @ref{Debugging, , Debugging Lisp Programs, elisp, The GNU Emacs Lisp Reference Manual}. In this chapter, I will walk through a short example of each. @menu * debug:: How to use the built-in debugger. * debug-on-entry:: Start debugging when you call a function. * debug-on-quit:: Start debugging when you quit with @kbd{C-g}. * edebug:: How to use Edebug, a source level debugger. * Debugging Exercises:: @end menu @node debug, debug-on-entry, Debugging, Debugging @section @code{debug} @findex debug Suppose you have written a function definition that is intended to return the sum of the numbers 1 through a given number. (This is the @code{triangle} function discussed earlier. @xref{Decrementing Example, , Example with Decrementing Counter}, for a discussion.) @c xref{Decrementing Loop,, Loop with a Decrementing Counter}, for a discussion.) However, your function definition has a bug. You have mistyped @samp{1=} for @samp{1-}. Here is the broken definition: @findex triangle-bugged @example @group (defun triangle-bugged (number) "Return sum of numbers 1 through NUMBER inclusive." (let ((total 0)) (while (> number 0) (setq total (+ total number)) (setq number (1= number))) ; @r{Error here.} total)) @end group @end example If you are reading this in Info, you can evaluate this definition in the normal fashion. You will see @code{triangle-bugged} appear in the echo area. @need 1250 Now evaluate the @code{triangle-bugged} function with an argument of 4: @example (triangle-bugged 4) @end example @noindent @example @group @exdent You will produce an error message that says: Symbol's function definition is void:@: 1= @end group @end example In practice, for a bug as simple as this, this error message will tell you what you need to know to correct the definition. However, suppose you are not quite certain what is going on? @findex debug-on-error You can turn on debugging by setting the value of @code{debug-on-error} to @code{t}: @example (setq debug-on-error t) @end example @noindent This causes Emacs to enter the debugger next time it encounters an error. @need 1250 @noindent You can turn off @code{debug-on-error} by setting it to @code{nil}: @example (setq debug-on-error nil) @end example @need 1250 @noindent Set @code{debug-on-error} to @code{t} and evaluate the following: @example (triangle-bugged 4) @end example @need 1250 @noindent This time, Emacs will create a buffer called @file{*Backtrace*} that looks like this: @example @group ---------- Buffer: *Backtrace* ---------- Signalling: (void-function 1=) (1= number)) (setq number (1= number))) (while (> number 0) (setq total (+ total number)) (setq number (1= number)))) (let ((total 0)) (while (> number 0) (setq total ...) (setq number ...)) total)) triangle-bugged(4) eval((triangle-bugged 4)) eval-last-sexp(nil) * call-interactively(eval-last-sexp) ---------- Buffer: *Backtrace* ---------- @end group @end example @noindent (I have reformatted this example slightly; the debugger does not fold long lines.) @cindex @file{*Backtrace*} buffer @cindex Backtrace buffer for debugging You read the @file{*Backtrace*} buffer from the bottom up; it tells you what Emacs did that led to the error. In this case, what Emacs did was make an interactive call to @kbd{C-x C-e} (@code{eval-last-sexp}), which led to the evaluation of the @code{triangle-bugged} expression. Each line above tells you what the Lisp interpreter evaluated next. @need 1250 The third line from the top of the buffer is @example (setq number (1= number)) @end example @noindent Emacs tried to evaluate this expression; in order to do so, it tried to evaluate the inner expression shown on the second line from the top: @example (1= number) @end example @need 1250 @noindent This is where the error occurred; as the top line says: @example Signalling: (void-function 1=) @end example @noindent You can correct the mistake, re-evaluate the function definition, and then run your test again. @need 1250 If you are reading this in Info, you can now turn off @code{debug-on-error} by setting it to @code{nil}: @example (setq debug-on-error nil) @end example @node debug-on-entry, debug-on-quit, debug, Debugging @section @code{debug-on-entry} @findex debug-on-entry A second way to start @code{debug} on a function is to enter the debugger when you call the function. You can do this by calling @code{debug-on-entry}. @need 1250 @noindent Type: @example M-x debug-on-entry RET triangle-bugged RET @end example @need 1250 @noindent Now, evaluate the following: @example (triangle-bugged 5) @end example @noindent Emacs will create a @file{*Backtrace*} buffer and tell you that it is beginning to evaluate the @code{triangle-bugged} function: @example @group ---------- Buffer: *Backtrace* ---------- Entering: * triangle-bugged(5) eval((triangle-bugged 5)) eval-last-sexp(nil) * call-interactively(eval-last-sexp) ---------- Buffer: *Backtrace* ---------- @end group @end example In the @file{*Backtrace*} buffer, type @kbd{d}. Emacs will evaluate the first expression in @code{triangle-bugged}; the buffer will look like this: @example @group ---------- Buffer: *Backtrace* ---------- Beginning evaluation of function call form: * (let ((total 0)) (while (> number 0) (setq total ...) (setq number ...)) total)) triangle-bugged(5) * eval((triangle-bugged 5)) eval-last-sexp(nil) * call-interactively(eval-last-sexp) ---------- Buffer: *Backtrace* ---------- @end group @end example @noindent Now, type @kbd{d} again, eight times, slowly. Each time you type @kbd{d}, Emacs will evaluate another expression in the function definition. Eventually, the buffer will look like this: @example @group ---------- Buffer: *Backtrace* ---------- Beginning evaluation of function call form: * (setq number (1= number))) * (while (> number 0) (setq total (+ total number)) (setq number (1= number)))) * (let ((total 0)) (while (> number 0) (setq total ...) (setq number ...)) total)) triangle-bugged(5) * eval((triangle-bugged 5)) eval-last-sexp(nil) * call-interactively(eval-last-sexp) ---------- Buffer: *Backtrace* ---------- @end group @end example @noindent Finally, after you type @kbd{d} two more times, Emacs will reach the error, and the top two lines of the @file{*Backtrace*} buffer will look like this: @example @group ---------- Buffer: *Backtrace* ---------- Signalling: (void-function 1=) * (1= number)) @dots{} ---------- Buffer: *Backtrace* ---------- @end group @end example By typing @kbd{d}, you were able to step through the function. You can quit a @file{*Backtrace*} buffer by typing @kbd{q}; this quits the trace, but does not cancel @code{debug-on-entry}. @findex cancel-debug-on-entry To cancel the effect of @code{debug-on-entry}, call @code{cancel-debug-on-entry} and the name of the function, like this: @example M-x cancel-debug-on-entry RET triangle-debugged RET @end example @noindent (If you are reading this in Info, cancel @code{debug-on-entry} now.) @node debug-on-quit, edebug, debug-on-entry, Debugging @section @code{debug-on-quit} and @code{(debug)} In addition to setting @code{debug-on-error} or calling @code{debug-on-entry}, there are two other ways to start @code{debug}. @findex debug-on-quit You can start @code{debug} whenever you type @kbd{C-g} (@code{keyboard-quit}) by setting the variable @code{debug-on-quit} to @code{t}. This is useful for debugging infinite loops. @cindex @code{(debug)} in code Or, you can insert a line that says @code{(debug)} into your code where you want the debugger to start, like this: @example @group (defun triangle-bugged (number) "Return sum of numbers 1 through NUMBER inclusive." (let ((total 0)) (while (> number 0) (setq total (+ total number)) (debug) ; @r{Start debugger.} (setq number (1= number))) ; @r{Error here.} total)) @end group @end example The @code{debug} function is described in detail in @ref{Debugger, , The Lisp Debugger, elisp, The GNU Emacs Lisp Reference Manual}. @node edebug, Debugging Exercises, debug-on-quit, Debugging @section The @code{edebug} Source Level Debugger @cindex Source level debugger @findex edebug Edebug normally displays the source of the code you are debugging, with an arrow at the left that shows which line you are currently executing. You can walk through the execution of a function, line by line, or run quickly until reaching a @dfn{breakpoint} where execution stops. Edebug is described in @ref{edebug, , Edebug, elisp, The GNU Emacs Lisp Reference Manual}. Here is a bugged function definition for @code{triangle-recursively}. @xref{Recursive triangle function, , Recursion in place of a counter}, for a review of it. This example is presented without indentation to the left of the @code{defun}, as explained below. @format @group @t{(defun triangle-recursively-bugged (number) "Return sum of numbers 1 through NUMBER inclusive. Uses recursion." (if (= number 1) 1 (+ number (triangle-recursively-bugged (1= number))))) ; @r{Error here.}} @end group @end format @noindent Normally, you would install this definition by positioning your cursor after the function's closing parenthesis and typing @kbd{C-x C-e} (@code{eval-last-sexp}) or else by positioning your cursor within the definition and typing @kbd{C-M-x} (@code{eval-defun}). (By default, the @code{eval-defun} command works only in Emacs Lisp mode or in Lisp Interactive mode.) However, to prepare this function definition for Edebug, you must first @dfn{instrument} the code using a different command. In Emacs version 19, you can do this by positioning your cursor within the definition and typing the following: @example M-x edebug-defun RET @end example @noindent This will cause Emacs to load Edebug automatically if it is not already loaded, and properly instrument the function. (After loading Edebug, you can use its standard keybindings, such as @kbd{C-u C-M-x} (@code{eval-defun} with a prefix argument) for @code{edebug-defun}.) In Emacs version 18, you need to load Edebug yourself; you can do this by putting the appropriate @code{load} command in your @file{.emacs} file. If you are reading this in Info, you can instrument the @code{triangle-recursively-bugged} function shown above. @code{edebug-defun} fails to locate the bounds of a definition whose @code{defun} line is indented; so the example is presented without the usual spaces to the left of the @code{defun}. After instrumenting the function, place your cursor after the following expression and type @kbd{C-x C-e} (@code{eval-last-sexp}): @example (triangle-recursively-bugged 3) @end example @noindent You will be jumped back to the source for @code{triangle-recursively-bugged} and the cursor positioned at the beginning of the @code{if} line of the function. Also, you will see an arrow at the left hand side of that line that looks like this: @samp{=>}. The arrow marks the line where the function is executing. @example =>@point{}(if (= number 1) @end example @noindent @iftex In the example, the location of point is displayed with a star, @samp{@point{}} (in Info, it is displayed as @samp{-!-}). @end iftex @ifinfo In the example, the location of point is displayed as @samp{@point{}} (in a printed book, it is displayed with a five pointed star). @end ifinfo If you now press @key{SPC}, point will move to the next expression to be executed; the line will look like this: @example =>(if @point{}(= number 1) @end example @noindent As you continue to press @key{SPC}, point will move from expression to expression. At the same time, whenever an expression returns a value, that value will be displayed in the echo area. For example, after you move point past @code{number}, you will see the following: @example Result: 3 = C-c @end example @noindent This means the value of @code{number} is 3, which is @sc{ascii} @key{CTL-C} (the third letter of the alphabet). You can continue moving through the code until you reach the line with the error. Before evaluation, that line looks like this: @example => @point{}(1= number))))) ; @r{Error here.} @end example @need 1250 @noindent When you press @key{SPC} once again, you will produce an error message that says: @example Symbol's function definition is void:@: 1= @end example @noindent This is the bug. Press @samp{q} to quit Edebug. To remove instrumentation from a function definition, simply re-evaluate it with a command that does not instrument it. For example, you could place your cursor after the definition's closing parenthesis and type @kbd{C-x C-e}. Edebug does a great deal more than walk with you through a function. You can set it so it races through on its own, stopping only at an error or at specified stopping points; you can cause it to display the changing values of various expressions; you can find out how many times a function is called, and more. Edebug is described in @ref{edebug, , Edebug, elisp, The GNU Emacs Lisp Reference Manual}. @need 1500 @node Debugging Exercises, , edebug, Debugging @section Debugging Exercises @itemize @bullet @item Install the @code{count-words-region} function and then cause it to enter the built-in debugger when you call it. Run the command on a region containing two words. You will need to press @kbd{d} a remarkable number of times. On your system, is a `hook' called after the command finishes? (For information on hooks, see @ref{Command Overview, , Command Loop Overview, elisp, The GNU Emacs Lisp Reference Manual}.) @item Copy @code{count-words-region} into the @file{*scratch*} buffer, remove white space before the @code{defun} line if necessary, instrument the function for Edebug, and walk through its execution. The function does not need to have a bug, although you can introduce one if you wish. If the function lacks a bug, the walk-through completes without problems. @item While running Edebug, type @kbd{?} to see a list of all the Edebug commands. (The @code{global-edebug-prefix} is usually @kbd{C-x X}, i.e.@: @kbd{@key{CTL}-x} followed by an upper case @kbd{X}; use this prefix for commands made outside of the Edebug debugging buffer.) @item In the Edebug debugging buffer, use the @kbd{p} (@code{edebug-bounce-point}) command to see where in the region the @code{count-words-region} is working. @item Move point to some spot further down function and then type the @kbd{h} (@code{edebug-goto-here}) command to jump to that location. @item Use the @kbd{t} (@code{edebug-trace-mode}) command to cause Edebug to walk through the function on its own; use an upper case @kbd{T} for @code{edebug-Trace-fast-mode}. @item Set a breakpoint, then run Edebug in Trace mode until it reaches the stopping point. @end itemize @node Conclusion, the-the, Debugging, Top @chapter Conclusion We have now reached the end of this Introduction. You have now learned enough about programming in Emacs Lisp to set values, to write simple @file{.emacs} files for yourself and your friends, and write simple customizations and extensions to Emacs. This is a place to stop. Or, if you wish, you can now go onward, and teach yourself. You have learned some of the basic nuts and bolts of programming. But only some. There are a great many more brackets and hinges that are easy to use that we have not touched. A path you can follow right now lies among the sources to GNU Emacs and in @iftex @cite{The GNU Emacs Lisp Reference Manual}. @end iftex @ifinfo @ref{Top, , The GNU Emacs Lisp Reference Manual, elisp, The GNU Emacs Lisp Reference Manual}. @end ifinfo The Emacs Lisp sources are an adventure. When you read the sources and come across a function or expression that is unfamiliar, you need to figure out or find out what it does. Go to the Reference Manual. It is a through, complete, and fairly easy-to-read description of Emacs Lisp. It is written not only for experts, but for people who know what you know. (The @cite{Reference Manual} comes with the standard GNU Emacs distribution. Like this introduction, it comes as a Texinfo source file, so you can read it on-line and as a typeset, printed book.) Go to the other on-line help that is part of GNU Emacs: the on-line documentation for all functions, and @code{find-tags}, the program that takes you to sources. Here is an example of how I explore the sources. Because of its name, @file{simple.el} is the file I looked at first, a long time ago. As it happens some of the functions in @file{simple.el} are complicated, or at least look complicated at first sight. The first function, for example, looks complicated. This is the @code{open-line} function. You may want to walk through this function slowly, as we did with the @code{forward-sentence} function. @ifinfo (@xref{forward-sentence}.) @end ifinfo @iftex (@xref{forward-sentence, , @code{forward-sentence}}.) @end iftex Or you may want to skip that function and look at another, such as @code{split-line}. You don't need to read all the functions. According to @code{count-words-in-defun}, the @code{split-line} function contains 27 words and symbols. Even though it is short, @code{split-line} contains four expressions we have not studied: @code{skip-chars-forward}, @code{indent-to}, @code{insert}, and @samp{?\n}. Consider the @code{insert} function. (It is mentioned in passing in @iftex the review section in @ref{Regexp Search, , Regular Expression Searches}.) @end iftex @ifinfo @ref{Regexp Review}.) @end ifinfo In Emacs, you can find out more about @code{insert} by typing @kbd{C-h f} (@code{describe-function}) and the name of the function. This gives you the function documentation. You can look at its source using @code{find-tag}, which is bound to @kbd{M-.} (this is not so helpful in this case; the function is a primitive written in C rather than Lisp). Finally, you can find out what the Reference Manual has to say by visiting the manual in Info, and typing @kbd{i} (@code{Info-index}) and the name of the function, or by looking up @code{insert} in the index to a printed copy of the manual. Similarly, you can find out what is meant by @samp{?\n}. You can try using @code{Info-index} with @samp{?\n}. It turns out that this action won't help; but don't give up. If you search the index for @samp{\n} without the @samp{?}, you will be taken directly to the relevant section of the manual. (@xref{Character Type, , Character Type, elisp, The GNU Emacs Lisp Reference Manual}. @samp{?\n} stands for the newline character.) You may be able to guess what is done by @code{skip-chars-forward} and @code{indent-to}; or you can look them up, too. (Incidentally, the @code{describe-function} function itself is in @file{help.el}; it is one of those long, but decipherable functions. Its definition illustrates how to customize the @code{interactive} expression without using the standard character codes; and it shows how to create a temporary buffer.) Other interesting source files include @file{paragraphs.el}, @file{loaddefs.el}, and @file{loadup.el}. The @file{paragraphs.el} file includes short, easily understood functions as well as longer ones. The @file{loaddefs.el} file contains the many standard autoloads and many keymaps. I have never looked at it all; only at parts. @file{loadup.el} is the file that loads the standard parts of Emacs; it tells you a great deal about how Emacs is built. (@xref{Building Emacs, , Building Emacs, elisp, The GNU Emacs Lisp Reference Manual}, for more about building.) As I said, you have learned some nuts and bolts; however, and very importantly, we have hardly touched major aspects of programming; I have said nothing about how to sort information, except to use the predefined @code{sort} function; I have nothing about how to store information, except to use variables and lists; I have said nothing about how to write programs that write programs. These are topics for another, and different kind of book, a different kind of learning. What you have done is learn enough for much practical work with GNU Emacs. What you have done is get started. This is the end of a beginning. @c ================ Appendix ================ @node the-the, Kill Ring, Conclusion, Top @appendix The @code{the-the} Function @findex the-the @cindex Duplicated words function @cindex Words, duplicated Sometimes when you you write text, you duplicate words---as with ``you you'' near the beginning of this sentence. I find that most frequently, I duplicate ``the'; hence, I call the function for detecting duplicated words, @code{the-the}. @need 1250 As a first step, you could use the following regular expression to search for duplicates: @example \\(\\w+[ \t\n]+\\)\\1 @end example @noindent This regexp matches one or more word-constituent characters followed by one or more spaces, tabs, or newlines. However, it does not detect duplicated words on different lines, since the ending of the first word, the end of the line, is different from the ending of the second word, a space. (For more information about regular expressions, see @ref{Regexp Search, , Regular Expression Searches}, as well as @ref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs Manual}, and @ref{Regular Expressions, , Regular Expressions, elisp, The GNU Emacs Lisp Reference Manual}.) You might try searching just for duplicated word-constituent characters but that does not work since the pattern detects doubles such as the two occurrences of `th' in `with the'. @c Kludge to reduce overfull hbox. (Ignore small hbox in largebook) @ifclear largebook Another possible regexp searches for word-constituent characters followed by non-word-constituent characters, reduplicated. Here, @w{@samp{\\w+}} matches one or more word-constituent characters and @w{@samp{\\W*}} matches zero or more non-word-constituent characters. @end ifclear @ifset largebook Another possible regular expression is for word-constituent characters that are followed by non-word-constituent characters. Here, @w{@samp{\\w+}} matches one or more word-constituent characters and @w{@samp{\\W*}} matches zero or more non-word-constituent characters. @end ifset @example \\(\\(\\w+\\)\\W*\\)\\1 @end example @noindent Again, not useful. Here is the pattern that I use. It is not perfect, but good enough. @w{@samp{\\b}} matches the empty string, provided it is at the beginning or end of a word; @w{@samp{[^@@ \n\t]+}} matches one or more occurrences of any characters that are @emph{not} an @@-sign, space, newline, or tab. @example \\b\\([^@@ \n\t]+\\)[ \n\t]+\\1\\b @end example One can write more complicated expressions, but I found that this expression is good enough, so I use it. Here is the @code{the-the} function, as I include it in my @file{.emacs} file, along with a handy global key binding: @example @group (defun the-the () "Search forward for for a duplicated word." (interactive) (message "Searching for for duplicated words ...") (push-mark) @end group @group ;; This regexp is not perfect ;; but is fairly good over all: (if (re-search-forward "\\b\\([^@@ \n\t]+\\)[ \n\t]+\\1\\b" nil 'move) (message "Found duplicated word.") (message "End of buffer"))) @end group @group ;; Bind `the-the' to C-c \ (global-set-key "\C-c\\" 'the-the) @end group @end example @sp 1 Here is test text: @example @group one two two three four five five six seven @end group @end example You can substitute the other regular expressions shown above in the function definition and try each of them on this list. @node Kill Ring, Full Graph, the-the, Top @appendix Handling the Kill Ring @cindex Kill ring handling @cindex Handling the kill ring @cindex Ring, making a list like a The kill ring is a list that is transformed into a ring by the workings of the @code{rotate-yank-pointer} function. The @code{yank} and @code{yank-pop} commands use the @code{rotate-yank-pointer} function. This appendix describes the @code{rotate-yank-pointer} function as well as both the @code{yank} and the @code{yank-pop} commands. @menu * rotate-yank-pointer:: Move a pointer along a list and around. * yank:: Paste a copy of a clipped element. * yank-pop:: Insert first element pointed to. @end menu @node rotate-yank-pointer, yank, Kill Ring, Kill Ring @comment node-name, next, previous, up @appendixsec The @code{rotate-yank-pointer} Function @findex rotate-yank-pointer The @code{rotate-yank-pointer} function changes the element in the kill ring to which @code{kill-ring-yank-pointer} points. For example, it can change @code{kill-ring-yank-pointer} from pointing to the second element to point to the third element. Here is the code for @code{rotate-yank-pointer}: @example @group (defun rotate-yank-pointer (arg) "Rotate the yanking point in the kill ring." (interactive "p") (let ((length (length kill-ring))) (if (zerop length) ;; @r{then-part} (error "Kill ring is empty") @end group @group ;; @r{else-part} (setq kill-ring-yank-pointer (nthcdr (% (+ arg (- length (length kill-ring-yank-pointer))) length) kill-ring))))) @end group @end example The function looks complex, but as usual, it can be understood by taking it apart piece by piece. First look at it in skeletal form: @example @group (defun rotate-yank-pointer (arg) "Rotate the yanking point in the kill ring." (interactive "p") (let @var{varlist} @var{body}@dots{}) @end group @end example This function takes one argument, called @code{arg}. It has a brief documentation string; and it is interactive with a small @samp{p}, which means that the argument must be a processed prefix passed to the function as a number. The body of the function definition is a @code{let} expression, which itself has a body as well as a @var{varlist}. The @code{let} expression declares a variable that will be only usable within the bounds of this function. This variable is called @code{length} and is bound to a value that is equal to the number of items in the kill ring. This is done by using the function called @code{length}. (Note that this function has the same name as the variable called @code{length}; but one use of the word is to name the function and the other is to name the variable. The two are quite distinct. Similarly, an English speaker will distinguish between the meanings of the word @samp{ship} when he says: "I must ship this package immediately." and "I must get aboard the ship immediately.") The function @code{length} tells the number of items there are in a list, so @code{(length kill-ring)} returns the number of items there are in the kill ring. @menu * rotate-yk-ptr body:: The Body of @code{rotate-yank-pointer}. @end menu @node rotate-yk-ptr body, , rotate-yank-pointer, rotate-yank-pointer @comment node-name, next, previous, up @appendixsubsec The Body of @code{rotate-yank-pointer} The body of @code{rotate-yank-pointer} is a @code{let} expression and the body of the @code{let} expression is an @code{if} expression. The purpose of the @code{if} expression is to find out whether there is anything in the kill ring. If the kill ring is empty, the @code{error} function stops evaluation of the function and prints a message in the echo area. On the other hand, if the kill ring has something in it, the work of the function is done. Here is the if-part and then-part of the @code{if} expression: @findex zerop @findex error @example @group (if (zerop length) ; @r{if-part} (error "Kill ring is empty") ; @r{then-part} @dots{} @end group @end example @noindent If there is not anything in the kill ring, its length must be zero and an error message sent to the user: @samp{Kill ring is empty}. The @code{if} expression uses the function @code{zerop} which returns true if the value it is testing is zero. When @code{zerop} tests true, the then-part of the @code{if} is evaluated. The then-part is a list starting with the function @code{error}, which is a function that is similar to the @code{message} function (@pxref{message}), in that it prints a one-line message in the echo area. However, in addition to printing a message, @code{error} also stops evaluation of the function within which it is embedded. In this case, this means that the rest of the function will not be evaluated if the length of the kill ring is zero. (In my opinion, it is slightly misleading, at least to humans, to use the term `error' as the name of this function. A better term would be `cancel'. Strictly speaking, of course, you cannot point to, much less rotate a pointer to a list that has no length, so from the point of view of the computer, the word `error' is correct. But a human expects to attempt this sort of thing, if only to find out whether the kill ring is full or empty. This is an act of exploration. (From the human point of view, the act of exploration and discovery is not necessarily an error, and therefore should not be labeled as one, even in the bowels of a computer. As it is, the code in Emacs implies that a human who is acting virtuously, by exploring his or her environment, is making an error. This is bad. Even though the computer takes the same steps as it does when there is an `error', a term such as `cancel' would have a clearer connotation.) @menu * rotate-yk-ptr else-part:: The else-part of the @code{if} expression. * Remainder Function:: The remainder, @code{%}, function. * rotate-yk-ptr remainder:: Using @code{%} in @code{rotate-yank-pointer}. * kill-rng-yk-ptr last elt:: Pointing to the last element. @end menu @node rotate-yk-ptr else-part, Remainder Function, rotate-yk-ptr body, rotate-yk-ptr body @unnumberedsubsubsec The else-part of the @code{if} expression The else-part of the @code{if} expression is dedicated to setting the value of @code{kill-ring-yank-pointer} when the kill ring has something in it. The code looks like this: @example @group (setq kill-ring-yank-pointer (nthcdr (% (+ arg (- length (length kill-ring-yank-pointer))) length) kill-ring))))) @end group @end example This needs some examination. Clearly, @code{kill-ring-yank-pointer} is being set to be equal to some @sc{cdr} of the kill ring, using the @code{nthcdr} function that is described in an earlier section. (@xref{copy-region-as-kill}.) But exactly how does it do this? Before looking at the details of the code let's first consider the purpose of the @code{rotate-yank-pointer} function. The @code{rotate-yank-pointer} function changes what @code{kill-ring-yank-pointer} points to. If @code{kill-ring-yank-pointer} starts by pointing to the first element of a list, a call to @code{rotate-yank-pointer} causes it to point to the second element; and if @code{kill-ring-yank-pointer} points to the second element, a call to @code{rotate-yank-pointer} causes it to point to the third element. (And if @code{rotate-yank-pointer} is given an argument greater than 1, it jumps the pointer that many elements.) The @code{rotate-yank-pointer} function uses @code{setq} to reset what the @code{kill-ring-yank-pointer} points to. If @code{kill-ring-yank-pointer} points to the first element of the kill ring, then, in the simplest case, the @code{rotate-yank-pointer} function must cause it to point to the second element. Put another way, @code{kill-ring-yank-pointer} must be reset to have a value equal to the @sc{cdr} of the kill ring. @need 1250 That is, under these circumstances, @example @group (setq kill-ring-yank-pointer ("some text" "a different piece of text" "yet more text")) (setq kill-ring ("some text" "a different piece of text" "yet more text")) @end group @end example @noindent the code should do this: @example (setq kill-ring-yank-pointer (cdr kill-ring)) @end example @noindent As a result, the @code{kill-ring-yank-pointer} will look like this: @example @group kill-ring-yank-pointer @result{} ("a different piece of text" "yet more text")) @end group @end example The actual @code{setq} expression uses the @code{nthcdr} function to do the job. As we have seen before (@pxref{nthcdr}), the @code{nthcdr} function works by repeatedly taking the @sc{cdr} of a list---it takes the @sc{cdr} of the @sc{cdr} of the @sc{cdr} @dots{} The two following expressions produce the same result: @example @group (setq kill-ring-yank-pointer (cdr kill-ring)) (setq kill-ring-yank-pointer (nthcdr 1 kill-ring)) @end group @end example In the @code{rotate-yank-pointer} function, however, the first argument to @code{nthcdr} is a rather complex looking expression with lots of arithmetic inside of it: @example @group (% (+ arg (- length (length kill-ring-yank-pointer))) length) @end group @end example As usual, we need to look at the most deeply embedded expression first and then work our way towards the light. The most deeply embedded expression is @code{(length kill-ring-yank-pointer)}. This finds the length of the current value of the @code{kill-ring-yank-pointer}. (Remember that the @code{kill-ring-yank-pointer} is the name of a variable whose value is a list.) The measurement of the length is inside the expression: @example (- length (length kill-ring-yank-pointer)) @end example @noindent In this expression, the first @code{length} is the variable that was assigned the length of the kill ring in the @code{let} statement at the beginning of the function. (One might think this function would be clearer if the variable @code{length} were named @code{length-of-kill-ring} instead; but if you look at the text of the whole function, you will see that it is so short that naming this variable @code{length} is not a bother, unless you are pulling the function apart into very tiny pieces as we are doing here.) So the line @code{(- length (length kill-ring-yank-pointer))} tells the difference between the length of the kill ring and the length of the list whose name is @code{kill-ring-yank-pointer}. To see how all this fits into the @code{rotate-yank-pointer} function, let's begin by analyzing the case where @code{kill-ring-yank-pointer} points to the first element of the kill ring, just as @code{kill-ring} does, and see what happens when @code{rotate-yank-pointer} is called with an argument of 1. In this case, the variable @code{length} and the value of the expression @code{(length kill-ring-yank-pointer} will be the same since the variable @code{length} is the length of the kill ring and the @code{kill-ring-yank-pointer} is pointing to the whole kill ring. Consequently, the value of @example (- length (length kill-ring-yank-pointer)) @end example @noindent will be zero. Since the value of @code{arg} will be 1, this will mean that the value of the whole expression @example (+ arg (- length (length kill-ring-yank-pointer))) @end example @noindent will be 1. Consequently, the argument to @code{nthcdr} will be found as the result of the expression @example (% 1 length) @end example @node Remainder Function, rotate-yk-ptr remainder, rotate-yk-ptr else-part, rotate-yk-ptr body @unnumberedsubsubsec The @code{%} remainder function To understand @code{(% 1 length)}, we need to understand @code{%}. According to its documentation (which I just found by typing @kbd{C-h f @key{%} @key{RET}}), the @code{%} function returns the remainder of its first argument divided by its second argument. For example, the remainder of 5 divided by 2 is 1. (2 goes into 5 twice with a remainder of 1.) What surprises people who don't often do arithmetic is that a smaller number can be divided by a larger number and have a remainder. In the example we just used, 5 was divided by 2. We can reverse that and ask, what is the result of dividing 2 by 5? If you can use fractions, the answer is obviously 2/5 or .4; but if, as here, you can only use whole numbers, the result has to be something different. Clearly, 5 can go into 2 zero times, but what of the remainder? To see what the answer is, consider a case that has to be familiar from childhood: @itemize @bullet @item 5 divided by 5 is 1 with a remainder of 0; @item 6 divided by 5 is 1 with a remainder of 1; @item 7 divided by 5 is 1 with a remainder of 2. @item Similarly, 10 divided by 5 is 2 with a remainder of 0; @item 11 divided by 5 is 2 with a remainder of 1; @item 12 divided by 5 is 1 with a remainder of 2. @end itemize @need 1250 @noindent By considering the cases as parallel, we can see that @itemize @bullet @item zero divided by 5 must be zero with a remainder of zero; @item 1 divided by 5 must be zero with a remainder of 1; @item 2 divided by 5 must be zero with a remainder of 2; @end itemize @noindent and so on. @need 1250 So, in this code, if the value of @code{length} is 5, then the result of evaluating @example (% 1 5) @end example @noindent is 1. (I just checked this by placing the cursor after the expression and typing @kbd{C-x C-e}. Indeed, 1 is printed in the echo area.) @node rotate-yk-ptr remainder, kill-rng-yk-ptr last elt, Remainder Function, rotate-yk-ptr body @unnumberedsubsubsec Using @code{%} in @code{rotate-yank-pointer} When the @code{kill-ring-yank-pointer} points to the beginning of the kill ring, and the argument passed to @code{rotate-yank-pointer} is 1, the @code{%} expression returns 1: @example @group (- length (length kill-ring-yank-pointer)) @result{} 0 @end group @end example @need 1250 @noindent therefore, @example @group (+ arg (- length (length kill-ring-yank-pointer))) @result{} 1 @end group @end example @need 1250 @noindent and consequently: @example @group (% (+ arg (- length (length kill-ring-yank-pointer))) length) @result{} 1 @end group @end example @noindent regardless of the value of @code{length}. @need 1250 @noindent As a result of this, the @code{setq kill-ring-yank-pointer} expression simplifies to: @example (setq kill-ring-yank-pointer (nthcdr 1 kill-ring)) @end example @noindent What it does is now easy to understand. Instead of pointing as it did to the first element of the kill ring, the @code{kill-ring-yank-pointer} is set to point to the second element. Clearly, if the argument passed to @code{rotate-yank-pointer} is two, then the @code{kill-ring-yank-pointer} is set to @code{(nthcdr 2 kill-ring)}; and so on for different values of the argument. Similarly, if the @code{kill-ring-yank-pointer} starts out pointing to the second element of the kill ring, it length is shorter than the length of the kill ring by 1, so the computation of the remainder is based on the expression @code{(% (+ arg 1) length)}. This means that the @code{kill-ring-yank-pointer} is moved from the second element of the kill ring to the third element if the argument passed to @code{rotate-yank-pointer} is 1. @node kill-rng-yk-ptr last elt, , rotate-yk-ptr remainder, rotate-yk-ptr body @unnumberedsubsubsec Pointing to the last element The final question is, what happens if the @code{kill-ring-yank-pointer} is set to the @emph{last} element of the kill ring? Will a call to @code{rotate-yank-pointer} mean that nothing more can be taken from the kill ring? The answer is no. What happens is different and useful. The @code{kill-ring-yank-pointer} is set to point to the beginning of the kill ring instead. Let's see how this works by looking at the code, assuming the length of the kill ring is 5 and the argument passed to @code{rotate-yank-pointer} is 1. When the @code{kill-ring-yank-pointer} points to the last element of the kill ring, its length is 1. The code looks like this: @example (% (+ arg (- length (length kill-ring-yank-pointer))) length) @end example @need 1250 When the variables are replaced by their numeric values, the expression looks like this: @example (% (+ 1 (- 5 1)) 5) @end example @noindent This expression can be evaluated by looking at the most embedded inner expression first and working outwards: The value of @code{(- 5 1)} is 4; the sum of @code{(+ 1 4)} is 5; and the remainder of dividing 5 by 5 is zero. So what @code{rotate-yank-pointer} will do is @example (setq kill-ring-yank-pointer (nthcdr 0 kill-ring)) @end example @noindent which will set the @code{kill-ring-yank-pointer} to point to the beginning of the kill ring. So what happens with successive calls to @code{rotate-yank-pointer} is that it moves the @code{kill-ring-yank-pointer} from element to element in the kill ring until it reaches the end; then it jumps back to the beginning. And this is why the kill ring is called a ring, since by jumping back to the beginning, it is as if the list has no end! (And what is a ring, but an entity with no end?) @node yank, yank-pop, rotate-yank-pointer, Kill Ring @comment node-name, next, previous, up @appendixsec @code{yank} @findex yank After learning about @code{rotate-yank-pointer}, the code for the @code{yank} function is almost easy. It has only one tricky part, which is the computation of the argument to be passed to @code{rotate-yank-pointer}. @need 1250 The code looks like this: @example @group (defun yank (&optional arg) "Reinsert the last stretch of killed text. More precisely, reinsert the stretch of killed text most recently killed OR yanked. With just C-U as argument, same but put point in front (and mark at end). With argument n, reinsert the nth most recently killed stretch of killed text. See also the command \\[yank-pop]." @end group @group (interactive "*P") (rotate-yank-pointer (if (listp arg) 0 (if (eq arg '-) -1 (1- arg)))) (push-mark (point)) (insert (car kill-ring-yank-pointer)) (if (consp arg) (exchange-point-and-mark))) @end group @end example Glancing over this code, we can understand the last few lines readily enough. The mark is pushed, that is, remembered; then the first element (the @sc{car}) of what the @code{kill-ring-yank-pointer} points to is inserted; and then, if the argument passed the function is a @code{cons}, point and mark are exchanged so the point is put in the front of the inserted text rather than at the end. This option is explained in the documentation. The function itself is interactive with @code{"*P"}. This means it will not work on a read-only buffer, and that the unprocessed prefix argument is passed to the function. @menu * rotate-yk-ptr arg:: Pass the argument to @code{rotate-yank-pointer}. * rotate-yk-ptr negative arg:: Pass a negative argument. @end menu @node rotate-yk-ptr arg, rotate-yk-ptr negative arg, yank, yank @unnumberedsubsubsec Passing the argument The hard part of @code{yank} is understanding the computation that determines the value of the argument passed to @code{rotate-yank-pointer}. Fortunately, it is not so difficult as it looks at first sight. What happens is that the result of evaluating one or both of the @code{if} expressions will be a number and that number will be the argument passed to @code{rotate-yank-pointer}. @need 1250 Laid out with comments, the code looks like this: @example @group (if (listp arg) ; @r{if-part} 0 ; @r{then-part} (if (eq arg '-) ; @r{else-part, inner if} -1 ; @r{inner if's then-part} (1- arg)))) ; @r{inner if's else-part} @end group @end example @noindent This code consists of two @code{if} expression, one the else-part of the other. The first or outer @code{if} expression tests whether the argument passed to @code{yank} is a list. Oddly enough, this will be true if @code{yank} is called without an argument---because then it will be passed the value of @code{nil} for the optional argument and an evaluation of @code{(listp nil)} returns true! So, if no argument is passed to @code{yank}, the argument passed to @code{rotate-yank-pointer} inside of @code{yank} is zero. This means the pointer is not moved and the first element to which @code{kill-ring-yank-pointer} points is inserted, as we expect. Similarly, if the argument for @code{yank} is @kbd{C-u}, this will be read as a list, so again, a zero will be passed to @code{rotate-yank-pointer}. (@kbd{C-u} produces an unprocessed prefix argument of @code{(4)}, which is a list of one element.) At the same time, later in the function, this argument will be read as a @code{cons} so point will be put in the front and mark at the end of the insertion. (The @code{P} argument to @code{interactive} is designed to provide these values for the case when an optional argument is not provided or when it is @kbd{C-u}.) The then-part of the outer @code{if} expression handles the case then there is no argument or when it is @kbd{C-u}. The else-part handles the other situations. The else-part is itself another @code{if} expression. The inner @code{if} expression tests whether the argument is a minus sign. (This is done by pressing the @key{META} and @kbd{-} keys at the same time, or the @key{ESC} key and then the @kbd{-} key). In this case, the @code{rotate-yank-pointer} function is passed @kbd{-1} as an argument. This moves the @code{kill-ring-yank-pointer} backwards, which is what is desired. If the true-or-false-test of the inner @code{if} expression is false (that is, if the argument is not a minus sign), the else-part of the expression is evaluated. This is the expression @code{(1- arg)}. Because of the two @code{if} expressions, it will only occur when the argument is a positive number or when it is a negative number (not just a minus sign on its own). What @code{(1- arg)} does is decrement the number and return it. (The @code{1-} function subtracts one from its argument.) This means that if the argument to @code{rotate-yank-pointer} is 1, it is reduced to zero, which means the first element to which @code{kill-ring-yank-pointer} points is yanked back, as you would expect. @node rotate-yk-ptr negative arg, , rotate-yk-ptr arg, yank @unnumberedsubsubsec Passing a negative argument Finally, the question arises, what happens if either the remainder function, @code{%}, or the @code{nthcdr} function is passed a negative argument, as they quite well may? The answers can be found by a quick test. When @code{(% -1 5)} is evaluated, a negative number is returned; and if @code{nthcdr} is called with a negative number, it returns the same value as if it were called with a first argument of zero. This can be seen be evaluating the following code. Here the @samp{@result{}} points to the result of evaluating the code preceding it. This was done by positioning the cursor after the code and typing @kbd{C-x C-e} (@code{eval-last-sexp}) in the usual fashion. You can do this if you are reading this in Info inside of GNU Emacs. @example @group (% -1 5) @result{} -1 @end group @group (setq animals '(cats dogs elephants)) @result{} (cats dogs elephants) @end group @group (nthcdr 1 animals) @result{} (dogs elephants) @end group @group (nthcdr 0 animals) @result{} (cats dogs elephants) @end group @group (nthcdr -1 animals) @result{} (cats dogs elephants) @end group @end example So, if a minus sign or a negative number is passed to @code{yank}, the @code{kill-ring-yank-point} is rotated backwards until it reaches the beginning of the list. Then it stays there. Unlike the other case, when it jumps from the end of the list to the beginning of the list, making a ring, it stops. This makes sense. You often want to get back to the most recently clipped out piece of text, but you don't usually want to insert text from as many as thirty kill commands ago. So you need to work through the ring to get to the end, but won't cycle around it inadvertently if you are trying to come back to the beginning. Incidentally, any number passed to @code{yank} with a minus sign preceding it will be treated as @minus{}1. This is evidently a simplification for writing the program. You don't need to jump back towards the beginning of the kill ring more than one place at a time and doing this is easier than writing a function to determine the magnitude of the number that follows the minus sign. @node yank-pop, , yank, Kill Ring @comment node-name, next, previous, up @appendixsec @code{yank-pop} @findex yank-pop After understanding @code{yank}, the @code{yank-pop} function is easy. Leaving out the documentation to save space, it looks like this: @example @group (defun yank-pop (arg) (interactive "*p") (if (not (eq last-command 'yank)) (error "Previous command was not a yank")) @end group @group (setq this-command 'yank) (let ((before (< (point) (mark)))) (delete-region (point) (mark)) (rotate-yank-pointer arg) @end group @group (set-mark (point)) (insert (car kill-ring-yank-pointer)) (if before (exchange-point-and-mark)))) @end group @end example The function is interactive with a small @samp{p} so the prefix argument is processed and passed to the function. The command can only be used after a previous yank; otherwise an error message is sent. This check uses the variable @code{last-command} which is discussed elsewhere. (@xref{copy-region-as-kill}.) The @code{let} clause sets the variable @code{before} to true or false depending whether point is before or after mark and then the region between point and mark is deleted. This is the region that was just inserted by the previous yank and it is this text that will be replaced. Next the @code{kill-ring-yank-pointer} is rotated so that the previously inserted text is not reinserted yet again. Mark is set at the beginning of the place the new text will be inserted and then the first element to which @code{kill-ring-yank-pointer} points is inserted. This leaves point after the new text. If in the previous yank, point was left before the inserted text, point and mark are now exchanged so point is again left in front of the newly inserted text. That is all there is to it! @node Full Graph, Index, Kill Ring, Top @appendix A Graph with Labelled Axes Printed axes help you understand a graph. They convey scale. In an earlier chapter (@pxref{Readying a Graph, , Readying a Graph}), we wrote the code to print the body of a graph. Here we write the code for print and labelling vertical and horizontal axes, along with the body itself. @menu * Labelled Example:: How a finished graph should look. * print-graph Varlist:: @code{let} expression in @code{print-graph}. * print-Y-axis:: Print a label for the vertical axis. * print-X-axis:: Print a horizontal label. * Print Whole Graph:: The function to print a complete graph. @end menu @node Labelled Example, print-graph Varlist, Full Graph, Full Graph @ifinfo @heading Labelled Example Graph @end ifinfo Since insertions fill a buffer to the right and below point, the new graph printing function should first print the Y or vertical axis, then the body of the graph, and finally the X or horizontal axis. This sequence lays out for us the contents of the function: @enumerate @item Set up code. @item Print Y axis. @item Print body of graph. @item Print X axis. @end enumerate Here is an example of how a finished graph should look: @example @group 10 - * * * * ** * *** 5 - * ******* * *** ******* ************* *************** 1 - **************** | | | | 1 5 10 15 @end group @end example @noindent In this graph, both the vertical and the horizontal axes are labeled with numbers. However, in some graphs, the horizontal axis is time and would be better labeled with months, like this: @example @group 5 - * * ** * ******* ********** ** 1 - ************** | ^ | Jan June Jan @end group @end example Indeed, with a little thought, we can easily come up with a variety of vertical and horizontal labelling schemes. Our task could become complicated. But complications breed confusion. Rather than permit this, it is better choose a simple labelling scheme for our first effort, and to modify or replace it later. These considerations suggest the following outline for the @code{print-graph} function: @example @group (defun print-graph (numbers-list) "@var{documentation}@dots{}" (let ((height @dots{} @dots{})) @end group @group (print-Y-axis height @dots{} ) (graph-body-print numbers-list) (print-X-axis @dots{} ))) @end group @end example We can work on each part of the @code{print-graph} function definition in turn. @node print-graph Varlist, print-Y-axis, Labelled Example, Full Graph @comment node-name, next, previous, up @appendixsec The @code{print-graph} Varlist @cindex @code{print-graph} varlist In writing the @code{print-graph} function, the first task is to write the varlist in the @code{let} expression. (We will leave aside for the moment any thoughts about making the function interactive or about the contents of its documentation string.) The varlist should set several values. Clearly, the top of the label for the vertical axis must be at least the height of the graph, which means that we must obtain this information here. Note that the @code{print-graph-body} function also requires this information. There is no reason to calculate the height of the graph in two different places, so we should change for @code{print-graph-body} from the way we defined it earlier to take advantage of the calculation. Similarly, both the function for printing the X axis labels and the @code{print-graph-body} function need to learn the value of the width of each symbol. We can perform the calculation here and change the definition for @code{print-graph-body} from the way we defined it in the previous chapter. The length of the label for the horizontal axis must be at least as long as the graph. However, this information is used only in the function that prints the horizontal axis, so it does not need to be calculated here. These thoughts lead us directly to the following form for the varlist in the @code{let} for @code{print-graph}: @example @group (let ((height (apply 'max numbers-list)) ; @r{First version.} (symbol-width (length graph-blank))) @end group @end example @noindent As we shall see, this expression is not quite right. @node print-Y-axis, print-X-axis, print-graph Varlist, Full Graph @comment node-name, next, previous, up @appendixsec The @code{print-Y-axis} Function @cindex Axis, print vertical @cindex Y axis printing @cindex Vertical axis printing @cindex Print vertical axis The job of the @code{print-Y-axis} function is to print a label for the vertical axis that looks like this: @example @group 10 - 5 - 1 - @end group @end example @noindent The function should be passed the height of the graph, and then should construct and insert the appropriate numbers and marks. It is easy enough to see in the figure what the Y axis label should look like; but to say in words, and then to write a function definition to do the job is another matter. It is not quite true to say that we want a number and a tick every five lines: there are only three lines between the @samp{1} and the @samp{5} (lines 2, 3, and 4), but four lines between the @samp{5} and the @samp{10} (lines 6, 7, 8, and 9). It is better to say that we want a number and a tick mark on the base line (number 1) and then that we want a number and a tick on the fifth line from the bottom and on every line that is a multiple of five. The next issue is what height the label should be. Suppose the maximum height of tallest column of the graph is seven. Should the highest label on the Y axis be @samp{5 -}, and should the graph stick up above the label? Or should the highest label be @samp{7 -}, and mark the peak of the graph? Or should the highest label be @code{10 -}, which is a multiple of five, and be higher than the topmost value of the graph? The latter form is preferred. Most graphs are drawn within rectangles whose sides are an integral number of steps long---5, 10, 15, and so on for a step distance of five. But as soon as we decide to use a step height for the vertical axis, we discover that the simple expression in the varlist for computing the height is wrong. The expression is @code{(apply 'max numbers-list)}. This returns the precise height, not the maximum height plus whatever is necessary to round up to the nearest multiple of five. A more complex expression is required. As usual in cases like this, a complex problem becomes simpler if it is divided into several smaller problems. First, consider the case when the highest value of the graph is an integral multiple of five---when it is 5, 10, 15 ,or some higher multiple of five. In this case, we can use this value as the Y axis height. A fairly simply way to determine whether a number is a multiple of five is to divide it by five and see if the division results in a remainder. If there is no remainder, the number is a multiple of five. Thus, seven divided by five has a remainder of two, and seven is not an integral multiple of five. Put in slightly different language, more reminiscent of the classroom, five goes into seven once, with a remainder of two. However, five goes into ten twice, with no remainder: ten is an integral multiple of five. @menu * Compute a Remainder:: How to compute the remainder of a division. * Y Axis Element:: Construct a line for the Y axis. * Y-axis-column:: Generate a list of Y axis labels. * print-Y-axis Final:: Print a vertical axis, final version. @end menu @node Compute a Remainder, Y Axis Element, print-Y-axis, print-Y-axis @appendixsubsec Side Trip: Compute a Remainder @findex % @r{(remainder function)} @cindex Remainder function, @code{%} In Lisp, the function for computing a remainder is @code{%}. The function returns the remainder of its first argument divided by its second argument. As it happens, @code{%} is a function in Emacs Lisp that you cannot discover using @code{apropos}: you find nothing if you type @kbd{M-x apropos @key{RET} remainder @key{RET}}. The only way to learn of the existence of @code{%} is to read about it in a book such as this or in the Emacs Lisp sources. The @code{%} function is used in the code for @code{rotate-yank-pointer}, which is described in an appendix. (@xref{rotate-yk-ptr body, , The Body of @code{rotate-yank-pointer}}.) You can try the @code{%} function by evaluating the following two expressions: @example @group (% 7 5) (% 10 5) @end group @end example @noindent The first expression returns 2 and the second expression returns 0. To test whether the returned value is zero or some other number, we can use the @code{zerop} function. This function returns @code{t} if its argument, which must be a number, is zero. @example @group (zerop (% 7 5)) @result{} nil (zerop (% 10 5)) @result{} t @end group @end example Thus, the following expression will return @code{t} if the height of the graph is evenly divisible by five: @example (zerop (% height 5)) @end example @noindent (The value of @code{height}, of course, can be found from @code{(apply 'max numbers-list)}.) On the other hand, if the value of @code{height} is not a multiple of five, we want to reset the value to the next higher multiple of five. This is straightforward arithmetic using functions with which we are already familiar. First, we divide the value of @code{height} by five to determine how many times five goes into the number. Thus, five goes into twelve twice. If we add one to this quotient and multiply by five, we will obtain the value of the next multiple of five that is larger than the height. Five goes into twelve twice. Add one to two, and multiply by five; the result is fifteen, with is the next multiple of five that is higher than twelve. The Lisp expression for this is: @example (* (1+ (/ height 5)) 5) @end example @noindent For example, if you evaluate the following, the result is 15: @example (* (1+ (/ 12 5)) 5) @end example All through this discussion, we have been using `five' as the value for spacing labels on the Y axis; but we may want to use some other value. For generality, we should replace `five' with a variable to which we can assign a value. The best name I can think of for this variable is @code{Y-axis-label-spacing}. Using this term, and an @code{if} expression, we produce the following: @example @group (if (zerop (% height Y-axis-label-spacing)) height ;; @r{else} (* (1+ (/ height Y-axis-label-spacing)) Y-axis-label-spacing)) @end group @end example @noindent This expression returns the value of @code{height} itself if the height is an even multiple of the value of the @code{Y-axis-label-spacing} or else it computes and returns a value of @code{height} that is equal to the next higher multiple of the value of the @code{Y-axis-label-spacing}. We can now include this expression in the @code{let} expression of the @code{print-graph} function (after first setting the value of @code{Y-axis-label-spacing}): @vindex Y-axis-label-spacing @example @group (defvar Y-axis-label-spacing 5 "Number of lines from one Y axis label to next.") @end group @group @dots{} (let* ((height (apply 'max numbers-list)) (height-of-top-line (if (zerop (% height Y-axis-label-spacing)) height @end group @group ;; @r{else} (* (1+ (/ height Y-axis-label-spacing)) Y-axis-label-spacing))) (symbol-width (length graph-blank)))) @dots{} @end group @end example @noindent (Note use of the @code{let*} function: the initial value of height is computed once by the @code{(apply 'max numbers-list)} expression and then the resulting value of @code{height} is used to compute its final value. @xref{fwd-para let, , The @code{let*} expression}, for more about @code{let*}.) @node Y Axis Element, Y-axis-column, Compute a Remainder, print-Y-axis @appendixsubsec Construct a Y Axis Element When we print the vertical axis, we want to insert strings such as @w{@samp{5 -}} and @w{@samp{10 - }} every five lines. Moreover, we want the numbers and dashes to line up, so shorter numbers must be padded with leading spaces. If some of the strings use two digit numbers, the strings with single digit numbers must include a leading blank space before the number. @findex int-to-string To figure out the length of the number, the @code{length} function is used. But the @code{length} function works only with a string, not with a number. So the number has to be converted from being a number to being a string. This is done with the @code{int-to-string} function. For example, @example @group (length (int-to-string 35)) @result{} 2 (length (int-to-string 100)) @result{} 3 @end group @end example In addition, in each label, each number is followed by a string such as @w{@samp{ - }}, which we will call the @code{Y-axis-tic} marker. This variable is defined with @code{defvar}: @vindex Y-axis-tic @example @group (defvar Y-axis-tic " - " "String that follows number in a Y axis label.") @end group @end example The length of the Y label is the sum of the length of the Y axis tick mark and the length of the number of the top of the graph. @example (length (concat (int-to-string height) Y-axis-tic))) @end example This value will be calculated by the @code{print-graph} function in its varlist as @code{full-Y-label-width} and passed on. (Note that we did not think to include this in the varlist when we first proposed it.) To make a complete vertical axis label, a tick mark is concatenated with a number; and the two together may be preceded by one or more spaces depending on how long the number is. The label consists of three parts: the (optional) leading spaces, the number, and the tic mark. The function is passed the value of the number for the specific row, and the value of the width of the top line, which is calculated (just once) by @code{print-graph}. @example @group (defun Y-axis-element (number full-Y-label-width) "Construct a NUMBERed label element. A numbered element looks like this ` 5 - ', and is padded as needed so all line up with the element for the largest number." @end group @group (let* ((leading-spaces (- full-Y-label-width (length (concat (int-to-string number) Y-axis-tic))))) @end group @group (concat (make-string leading-spaces ? ) (int-to-string number) Y-axis-tic))) @end group @end example The @code{Y-axis-element} function concatenates together the leading spaces, if any; the number, as a string; and the tick mark. To figure out how many leading spaces the label will need, the function subtracts the actual length of the label---the length of the number plus the length of the tic mark---from the desired label width. @findex make-string Blank spaces are inserted using the @code{make-string} function. This function takes two arguments: the first tells it how long the string will be and the second is a symbol for the character to insert, in a special format. In this case, the format is a question mark followed by a blank space, like this, @samp{? }. @xref{Character Type, , Character Type, elisp, The GNU Emacs Lisp Reference Manual}, for a description of the syntax for characters. The @code{int-to-string} function is used in the concatenation expression, to convert the number to a string that is concatenated with the leading spaces and the tic mark. @node Y-axis-column, print-Y-axis Final, Y Axis Element, print-Y-axis @appendixsubsec Create a Y Axis Column The preceding functions provide all the tools needed to construct a function that generates a list of numbered and blank strings to insert as the label for the vertical axis: @findex Y-axis-column @example @group (defun Y-axis-column (height width-of-label) "Construct list of Y axis labels and blank strings. For HEIGHT of line above base and WIDTH-OF-LABEL." (let (Y-axis) @group @end group (while (> height 1) (if (zerop (% height Y-axis-label-spacing)) ;; @r{Insert label.} (setq Y-axis (cons (Y-axis-element height width-of-label) Y-axis)) @group @end group ;; @r{Else, insert blanks.} (setq Y-axis (cons (make-string width-of-label ? ) Y-axis))) (setq height (1- height))) ;; @r{Insert base line.} (setq Y-axis (cons (Y-axis-element 1 width-of-label) Y-axis)) (nreverse Y-axis))) @end group @end example In this function, we start with the value of @code{height} and repetitively subtract one from its value. After each subtraction, we test to see whether the value is an integral multiple of the @code{Y-axis-label-spacing}. If it is, we construct a numbered label using the @code{Y-axis-element} function; if not, we construct a blank label using the @code{make-string} function. The base line consists of the number one followed by a tic mark. @node print-Y-axis Final, , Y-axis-column, print-Y-axis @appendixsubsec Final Version of @code{print-Y-axis} The list constructed by the @code{Y-axis-column} function is passed to the @code{print-Y-axis} function, which inserts the list as a column. @findex print-Y-axis @example @group (defun print-Y-axis (height full-Y-label-width &optional vertical-step) "Insert Y axis using HEIGHT and FULL-Y-LABEL-WIDTH. Height must be the maximum height of the graph. Full width is the width of the highest label element. Optionally, print according to VERTICAL-STEP." ;; Value of height and full-Y-label-width ;; are passed by `print-graph'. @end group @group (let ((start (point))) (insert-rectangle (Y-axis-column height full-Y-label-width vertical-step)) ;; @r{Place point ready for inserting graph.} (goto-char start) ;; @r{Move point forward by value of} full-Y-label-width (forward-char full-Y-label-width))) @end group @end example The @code{print-Y-axis} uses the @code{insert-rectangle} function to insert the Y axis labels created by the @code{Y-axis-column} function. In addition, it places point at the correct position for printing the body of the graph. You can test @code{print-Y-axis}: @enumerate @item Install @example @group Y-axis-label-spacing Y-axis-tic Y-axis-element Y-axis-columnprint-Y-axis @end group @end example @item Copy the following expression: @example (print-Y-axis 12 5) @end example @item Switch to the @file{*scratch*} buffer and place the cursor where you want the axis labels to start. @item Type @kbd{M-@key{ESC}} (@code{eval-expression}). @item Yank the @code{graph-body-print} expression into the minibuffer with @kbd{C-y} (@code{yank)}. @item Press @key{RET} to evaluate the expression. @end enumerate Emacs will print labels vertically, the top one being @w{@samp{10 -@w{ }}}. (The @code{print-graph} function will pass the value of @code{height-of-top-line}, which in this case would be 15.) @node print-X-axis, Print Whole Graph, print-Y-axis, Full Graph @appendixsec The @code{print-X-axis} Function @cindex Axis, print horizontal @cindex X axis printing @cindex Print horizontal axis @cindex Horizontal axis printing X axis labels are much like Y axis labels, except that the tics are on a line above the numbers. Labels should look like this: @example @group | | | | 1 5 10 15 @end group @end example The first tic is under the first column of the graph and is preceded by several blank spaces. These spaces provide room in rows above for the Y axis labels. The second, third, fourth, and subsequent tics are all spaced equally, according to the value of @code{X-axis-label-spacing}. The second row of the X axis consists of numbers, preceded by several blank spaces and also separated according to the value of the variable @code{X-axis-label-spacing}. The value of the variable @code{X-axis-label-spacing} should itself be measured in units of @code{symbol-width}, since you may want to change the width of the symbols that you are using to print the body of the graph without changing the ways the graph is labeled. The @code{print-X-axis} function is constructed in more or less the same fashion as the @code{print-Y-axis} function except that it has two lines: the line of tic marks and the numbers. We will write a separate function to print each line and then combine them within the @code{print-X-axis} function. This is a three step process: @enumerate @item Write a function to print the X axis tic marks, @code{print-X-axis-tic-line}. @item Write a function to print the X numbers, @code{print-X-axis-numbered-line}. @item Write a function to print both lines, the @code{print-X-axis} function, using @code{print-X-axis-tic-line} and @code{print-X-axis-numbered-line}. @end enumerate @menu * X Axis Tic Marks:: Create tic marks for the horizontal axis. @end menu @node X Axis Tic Marks, , print-X-axis, print-X-axis @appendixsubsec X Axis Tic Marks The first function should print the X axis tic marks. We must specify the tic marks themselves and their spacing: @example @group (defvar X-axis-label-spacing (if (boundp 'graph-blank) (* 5 (length graph-blank)) 5) "Number of units from one X axis label to next.") @end group @end example @noindent (Note that the value of @code{graph-blank} is set by another @code{defvar}. The @code{boundp} predicate checks whether it has already been set; @code{boundp} returns @code{nil} if it has not. If @code{graph-blank} were unbound and we did not use this conditional construction, we would receive an error message saying @samp{Symbol's value as variable is void}.) @example @group (defvar X-axis-tic-symbol "|" "String to insert to point to a column in X axis.") @end group @end example @need 1250 The goal is to make a line that looks like this: @example | | | | @end example The first tic is indented so that it is under the first column, which is indented to provide space for the Y axis labels. A tic element consists of the blank spaces that stretch from one tic to the next plus a tic symbol. The number of blanks is determined by the width of the tic symbol and the @code{X-axis-label-spacing}. @need 1250 The code looks like this: @example @group ;;; X-axis-tic-element @dots{} (concat (make-string ;; @r{Make a string of blanks.} (- (* symbol-width X-axis-label-spacing) (length X-axis-tic-symbol)) ? ) ;; @r{Concatenate blanks with tic symbol.} X-axis-tic-symbol) @dots{} @end group @end example Next, we determine how many blanks are needed to indent the first tic mark to the first column of the graph. This uses the value of @code{full-Y-label-width} passed it by the @code{print-graph} function. @need 1250 The code to make @code{X-axis-leading-spaces} looks like this: @example @group ;; X-axis-leading-spaces @dots{} (make-string full-Y-label-width ? ) @dots{} @end group @end example We also need to determine the length of the horizontal axis, which is the length of the numbers list, and the number of tics in the horizontal axis: @example @group ;; X-length @dots{} (length numbers-list) @end group @group ;; tic-width @dots{} (* symbol-width X-axis-label-spacing) @end group @group ;; number-of-X-tics (if (zerop (% (X-length tic-width))) (/ (X-length tic-width)) (1+ (/ (X-length tic-width)))) @end group @end example @need 1250 All this leads us directly to the function for printing the X axis tic line: @findex print-X-axis-tic-line @example @group (defun print-X-axis-tic-line (number-of-X-tics X-axis-leading-spaces X-axis-tic-element) "Print tics for X axis." (insert X-axis-leading-spaces) (insert X-axis-tic-symbol) ; @r{Under first column.} @end group @group ;; @r{Insert second tic in the right spot.} (insert (concat (make-string (- (* symbol-width X-axis-label-spacing) ;; @r{Insert white space up to second tic symbol.} (* 2 (length X-axis-tic-symbol))) ? ) X-axis-tic-symbol)) @end group @group ;; @r{Insert remaining tics.} (while (> number-of-X-tics 1) (insert X-axis-tic-element) (setq number-of-X-tics (1- number-of-X-tics)))) @end group @end example The line of numbers is equally straightforward: @need 1250 First, we create a numbered element with blank spaces before each number: @findex X-axis-element @example @group (defun X-axis-element (number) "Construct a numbered X axis element." (let ((leading-spaces (- (* symbol-width X-axis-label-spacing) (length (int-to-string number))))) (concat (make-string leading-spaces ? ) (int-to-string number)))) @end group @end example Next, we create the function to print the numbered line, starting with the number ``1'' under the first column: @findex print-X-axis-numbered-line @example @group (defun print-X-axis-numbered-line (number-of-X-tics X-axis-leading-spaces) "Print line of X-axis numbers" (let ((number X-axis-label-spacing)) (insert X-axis-leading-spaces) (insert "1") @end group @group (insert (concat (make-string ;; @r{Insert white space up to next number.} (- (* symbol-width X-axis-label-spacing) 2) ? ) (int-to-string number))) @end group @group ;; @r{Insert remaining numbers.} (setq number (+ number X-axis-label-spacing)) (while (> number-of-X-tics 1) (insert (X-axis-element number)) (setq number (+ number X-axis-label-spacing)) (setq number-of-X-tics (1- number-of-X-tics))))) @end group @end example Finally, we need to write the @code{print-X-axis} that uses @code{print-X-axis-tic-line} and @code{print-X-axis-numbered-line}. The function must determine the local values of the variables used by both @code{print-X-axis-tic-line} and @code{print-X-axis-numbered-line}, and then it must call them. Also, it must print the carriage return that separates the two lines. The function consists of a varlist that specifies five local variables, and calls to each of the two line printing functions: @findex print-X-axis @example @group (defun print-X-axis (numbers-list) "Print X axis labels to length of NUMBERS-LIST." (let* ((leading-spaces (make-string full-Y-label-width ? )) @end group @group ;; symbol-width @r{is provided by} graph-body-print (tic-width (* symbol-width X-axis-label-spacing)) (X-length (length numbers-list)) @end group @group (X-tic (concat (make-string @end group @group ;; @r{Make a string of blanks.} (- (* symbol-width X-axis-label-spacing) (length X-axis-tic-symbol)) ? ) @end group @group ;; @r{Concatenate blanks with tic symbol.} X-axis-tic-symbol)) @end group @group (tic-number (if (zerop (% X-length tic-width)) (/ X-length tic-width) (1+ (/ X-length tic-width))))) @end group @group (print-X-axis-tic-line tic-number leading-spaces X-tic) (insert "\n") (print-X-axis-numbered-line tic-number leading-spaces))) @end group @end example @need 1250 You can test @code{print-X-axis}: @enumerate @item Install @code{X-axis-tic-symbol}, @code{X-axis-label-spacing}, @code{print-X-axis-tic-line}, as well as @code{X-axis-element}, @code{print-X-axis-numbered-line}, and @code{print-X-axis}. @item Copy the following expression: @example @group (progn (let ((full-Y-label-width 5) (symbol-width 1)) (print-X-axis '(1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16)))) @end group @end example @item Switch to the @file{*scratch*} buffer and place the cursor where you want the axis labels to start. @item Type @kbd{M-@key{ESC}} (@code{eval-expression}). @item Yank the test expression into the minibuffer with @kbd{C-y} (@code{yank)}. @item Press @key{RET} to evaluate the expression. @end enumerate @need 1250 Emacs will print the horizontal axis like this: @example @group | | | | | 1 5 10 15 20 @end group @end example @node Print Whole Graph, , print-X-axis, Full Graph @appendixsec Printing the Whole Graph @cindex Printing the whole graph @cindex Whole graph printing @cindex Graph, printing all Now we are nearly ready to print the whole graph. The function to print the graph with the proper labels follows the outline we created earlier (@pxref{Full Graph, , A Graph with Labelled Axes}), but with additions. @need 1250 Here is the outline: @example @group (defun print-graph (numbers-list) "@var{documentation}@dots{}" (let ((height @dots{} @dots{})) @end group @group (print-Y-axis height @dots{} ) (graph-body-print numbers-list) (print-X-axis @dots{} ))) @end group @end example The final version is different from what we planned in two ways: first, it contains additional values calculated once in the varlist; second, it carries an option to specify the labels' increment per row. This latter feature turns out to be essential; otherwise a graph may have more rows than fit on a display or on a sheet of paper. This new feature requires a change to the @code{Y-axis-column} function, to add @code{vertical-step} to it. The function looks like this: @findex Y-axis-column @r{Final version.} @example @group ;;; @r{Final version.} (defun Y-axis-column (height width-of-label &optional vertical-step) "Construct list of labels for Y axis. HEIGHT is maximum height of graph. WIDTH-OF-LABEL is maximum width of label. VERTICAL-STEP, an option, is a positive integer that specifies how much a Y axis label increments for each line. For example, a step of 5 means that each line is five units of the graph." @end group @group (let (Y-axis (number-per-line (or vertical-step 1))) (while (> height 1) (if (zerop (% height Y-axis-label-spacing)) @end group @group ;; @r{Insert label.} (setq Y-axis (cons (Y-axis-element (* height number-per-line) width-of-label) Y-axis)) @end group @group ;; @r{Else, insert blanks.} (setq Y-axis (cons (make-string width-of-label ? ) Y-axis))) (setq height (1- height))) @end group @group ;; @r{Insert base line.} (setq Y-axis (cons (Y-axis-element (or vertical-step 1) width-of-label) Y-axis)) (nreverse Y-axis))) @end group @end example The values for the maximum height of graph and the width of a symbol are computed by @code{print-graph} in its @code{let} expression; so @code{graph-body-print} must be changed to accept them. @findex graph-body-print @r{Final version.} @example @group ;;; @r{Final version.} (defun graph-body-print (numbers-list height symbol-width) "Print a bar graph of the NUMBERS-LIST. The numbers-list consists of the Y-axis values. HEIGHT is maximum height of graph. SYMBOL-WIDTH is number of each column." @end group @group (let (from-position) (while numbers-list (setq from-position (point)) (insert-rectangle (column-of-graph height (car numbers-list))) (goto-char from-position) (forward-char symbol-width) @end group @group ;; @r{Draw graph column by column.} (sit-for 0) (setq numbers-list (cdr numbers-list))) ;; @r{Place point for X axis labels.} (forward-line height) (insert "\n"))) @end group @end example @need 1250 Finally, the code for the @code{print-graph} function: @findex print-graph @r{Final version.} @example @group ;;; @r{Final version.} (defun print-graph (numbers-list &optional vertical-step) "Print labelled bar graph of the NUMBERS-LIST. The numbers-list consists of the Y-axis values. @end group @group Optionally, VERTICAL-STEP, a positive integer, specifies how much a Y axis label increments for each line. For example, a step of 5 means that each row is five units." @end group @group (let* ((symbol-width (length graph-blank)) ;; @code{height} @r{is both the largest number} ;; @r{and the number with the most digits.} (height (apply 'max numbers-list)) @end group @group (height-of-top-line (if (zerop (% height Y-axis-label-spacing)) height ;; @r{else} (* (1+ (/ height Y-axis-label-spacing)) Y-axis-label-spacing))) @end group @group (vertical-step (or vertical-step 1)) (full-Y-label-width (length @end group @group (concat (int-to-string (* height-of-top-line vertical-step)) Y-axis-tic)))) @end group @group (print-Y-axis height-of-top-line full-Y-label-width vertical-step) @end group @group (graph-body-print numbers-list height-of-top-line symbol-width) (print-X-axis numbers-list))) @end group @end example @menu * Test print-graph:: Run a short test. * Graphing words in defuns:: Executing the final code. * Final Printed Graph:: The graph itself! @end menu @node Test print-graph, Graphing words in defuns, Print Whole Graph, Print Whole Graph @appendixsubsec Testing @code{print-graph} @need 1250 We can test the @code{print-graph} function with a short list of numbers @enumerate @item Install the final versions of @code{Y-axis-column}, @code{graph-body-print}, and @code{print-graph} (in addition to the rest of the code.) @item Copy the following expression: @example (print-graph '(3 2 5 6 7 5 3 4 6 4 3 2 1)) @end example @item Switch to the @file{*scratch*} buffer and place the cursor where you want the axis labels to start. @item Type @kbd{M-@key{ESC}} (@code{eval-expression}). @item Yank the test expression into the minibuffer with @kbd{C-y} (@code{yank)}. @item Press @key{RET} to evaluate the expression. @end enumerate @need 1250 Emacs will print a graph that looks like this: @example @group 10 - * ** * 5 - **** * **** *** * ********* ************ 1 - ************* | | | | 1 5 10 15 @end group @end example On the other hand, if you pass @code{print-graph} a @code{vertical-step} value of 2, by evaluating this expression: @example (print-graph '(3 2 5 6 7 5 3 4 6 4 3 2 1) 2) @end example @need 1250 @noindent The graph looks like this: @example @group 20 - * ** * 10 - **** * **** *** * ********* ************ 2 - ************* | | | | 1 5 10 15 @end group @end example @noindent (A question: is the `2' on the bottom of the vertical axis a bug or a feature? If you think it is a bug, and should be a `1' instead, (or even a `0'), you can modify the sources.) @node Graphing words in defuns, Final Printed Graph, Test print-graph, Print Whole Graph @appendixsubsec Graphing Numbers of Words and Symbols Now for the graph for which all this code was written: a graph that shows how many function definitions contain fewer than 10 words and symbols, how many contain between 10 and 19 words and symbols, how many contain between 20 and 29 words and symbols, and so on. This is a multi-step process. First make sure you have loaded all the requisit code. It is a good idea to reset the value of @code{top-of-ranges} in case you have sent it to some different value. You can evaluate the following: @example @group (setq top-of-ranges '(10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300) @end group @end example @noindent Next create a list of the number of words and symbols in each range. @need 1500 @noindent Evaluate the following: @example @group (setq list-for-graph (defuns-per-range (sort (recursive-lengths-list-many-files (directory-files "/usr/local/emacs/lisp" t ".+el$")) '<) top-of-ranges)) @end group @end example @noindent On my machine, this takes about an hour. It looks though 303 Lisp files in my copy of Emacs version 19.23. After all that computing, the @code{list-for-graph} has this value: @example @group (537 1027 955 785 594 483 349 292 224 199 166 120 116 99 90 80 67 48 52 45 41 33 28 26 25 20 12 28 11 13 220) @end group @end example @noindent This means that my copy of Emacs has 537 function definitions with fewer than 10 words or symbols in them, 1,027 function definitions with 10 to 19 words or symbols in them, 955 function definitions with 20 to 29 words or symbols in them, and so on. Clearly, just by looking at this list we can see that most function definitions contain ten to thirty words and symbols. Now for printing. We do @emph{not} want to print a graph that is 1,030 lines high @dots{} Instead, we should print a graph that is fewer than twenty-five lines high. A graph that height can be displayed on almost any monitor, and easily printed on a sheet of paper. This means that each value in @code{list-for-graph} must be reduced to one-fiftieth it present value. Here is a short function to do just that, using two functions we have not yet seen, @code{mapcar} and @code{lambda}. @example @group (defun one-fiftieth (full-range) "Return list, each number one-fiftieth of previous." (mapcar '(lambda (arg) (/ arg 50)) full-range)) @end group @end example @menu * lambda:: How to write an anonymous function. * mapcar:: Apply a function to elements of a list. * Another Bug:: Yet another @dots{} of a most insidious type. @end menu @node lambda, mapcar, Graphing words in defuns, Graphing words in defuns @unnumberedsubsubsec A @code{lambda} Expression @cindex Anonymous function @findex lambda @code{lambda} is the symbol for an anonymous function, a function without a name. Every time you use an anonymous function, you need to include its whole body. @need 1250 @noindent Thus, @example (lambda (arg) (/ arg 50)) @end example @noindent is a function definition that says `return the value resulting from dividing whatever is passed to me as @code{arg} by 50'. Earlier, for example, we had a function @code{multiply-by-seven}; it multiplied its argument by 7. This function is similar, except it divides its argument by 50; and, it has no name. The anonymous equivalent of @code{multiply-by-seven} is: @example (lambda (number) (* 7 number)) @end example @noindent (@xref{defun, , The @code{defun} Special Form}.) @need 1250 @noindent If we want to multiply 3 by 7, we can write: @c !!! Clear if machine is too small and cannot handle all 10 figures. @c lear print-postscript-figures @c set print-postscript-figures @c lambda example diagram #1 @ifinfo @example @group (multiply-by-seven 3) \_______________/ ^ | | function argument @end group @end example @end ifinfo @ifset print-postscript-figures @sp 1 @tex \input /usr/local/lib/tex/inputs/psfig.tex \centerline{\psfig{figure=/usr/local/lib/emacs/man/lambda-diagram1.eps}} \catcode`\@=0 % @end tex @sp 1 @end ifset @ifclear print-postscript-figures @iftex @example @group (multiply-by-seven 3) \_______________/ ^ | | function argument @end group @end example @end iftex @end ifclear @noindent This expression returns 21. @need 1250 @noindent Similarly, we can write: @c lambda example diagram #2 @ifinfo @example @group ((lambda (number) (* 7 number)) 3) \____________________________/ ^ | | anonymous function argument @end group @end example @end ifinfo @ifset print-postscript-figures @sp 1 @tex \input /usr/local/lib/tex/inputs/psfig.tex \centerline{\psfig{figure=/usr/local/lib/emacs/man/lambda-diagram2.eps}} \catcode`\@=0 % @end tex @sp 1 @end ifset @ifclear print-postscript-figures @iftex @example @group ((lambda (number) (* 7 number)) 3) \____________________________/ ^ | | anonymous function argument @end group @end example @end iftex @end ifclear @need 1250 @noindent If we want to divide 100 by 50, we can write: @c lambda example diagram #3 @ifinfo @example @group ((lambda (arg) (/ arg 50)) 100) \______________________/ \_/ | | anonymous function argument @end group @end example @end ifinfo @ifset print-postscript-figures @sp 1 @tex \input /usr/local/lib/tex/inputs/psfig.tex \centerline{\psfig{figure=/usr/local/lib/emacs/man/lambda-diagram3.eps}} \catcode`\@=0 % @end tex @sp 1 @end ifset @ifclear print-postscript-figures @iftex @example @group ((lambda (arg) (/ arg 50)) 100) \______________________/ \_/ | | anonymous function argument @end group @end example @end iftex @end ifclear @noindent This expression returns 2. The 100 is passed to the function, which divides that number by 50. @xref{Lambda Expressions, , Lambda Expressions, elisp, The GNU Emacs Lisp Reference Manual}, for more about @code{lambda}. Lisp and lambda expressions derive from the Lambda Calculus. @node mapcar, Another Bug, lambda, Graphing words in defuns @unnumberedsubsubsec The @code{mapcar} Function @findex mapcar @code{mapcar} is a function that calls its first argument with each element of its second argument, in turn. The second argument must be a sequence. @need 1250 @noindent For example, @example @group (mapcar '1+ '(2 4 6)) @result{} (3 5 7) @end group @end example @noindent The function @code{1+} which adds one to its argument, is executed on @emph{each} element of the list, and a new list is returned. Contrast this with @code{apply}, which applies its first argument to all the remaining. (@xref{Readying a Graph, , Readying a Graph}, for a explanation of @code{apply}.) @need 1250 In the definition of @code{one-fiftieth}, the first argument is the anonymous function: @example (lambda (arg) (/ arg 50)) @end example @noindent and the second argument is @code{full-range}, which will be bound to @code{list-for-graph}. @need 1250 The whole expression looks like this: @example (mapcar '(lambda (arg) (/ arg 50)) full-range)) @end example @xref{Mapping Functions, , Mapping Functions, elisp, The GNU Emacs Lisp Reference Manual}, for more about @code{mapcar}. Using the @code{one-fiftieth} function, we can generate a list in which each element is one-fiftieth the size of the corresponding element in @code{list-for-graph}. @example @group (setq fiftieth-list-for-graph (one-fiftieth list-for-graph)) @end group @end example @need 1250 The resulting list looks like this: @example @group (10 20 19 15 11 9 6 5 4 3 3 2 2 1 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 4) @end group @end example @noindent This we are almost ready to print! (We also notice the loss of information: many of the higher ranges are 0, meaning that fewer than 50 defuns had that many words or symbols---but not necessarily meaning that none had that many words or symbols.) @node Another Bug, , mapcar, Graphing words in defuns @unnumberedsubsubsec Another Bug @dots{} Most Insidious @cindex Bug, most insidious type @cindex Insidious type of bug I said `almost ready to print'! Of course, there is a bug in the @code{print-graph} function @dots{} It has a @code{vertical-step} option, but not a @code{horizontal-step} option. The @code{top-of-range} scale goes from 10 to 300 by tens. But the @code{print-graph} function will print only by ones. This is a classic example of what some consider the most insidious type of bug, the bug of omission. This is not the kind of bug you can find by studying the code, for it is not in the code; it is an omitted feature. Your best actions are to try your program early and often; and try to arrange, as much as you can, to write code that is easy to understand and easy to change. Try to be aware, whenever you can, that whatever you have written, @emph{will} be rewritten, if not soon, eventually. A hard maxim to follow. It is the @code{print-X-axis-numbered-line} function that needs the work; and then the @code{print-X-axis} and the @code{print-graph} functions need to be adapted. Not much needs to be done; there is one nicety: the numbers ought to line up under the tic marks. This takes a little thought. @need 1250 Here is the corrected @code{print-X-axis-numbered-line}: @example @group (defun print-X-axis-numbered-line (number-of-X-tics X-axis-leading-spaces &optional horizontal-step) "Print line of X-axis numbers" (let ((number X-axis-label-spacing) (horizontal-step (or horizontal-step 1))) @end group @group (insert X-axis-leading-spaces) ;; @r{Delete extra leading spaces.} (delete-char (- (1- (length (int-to-string horizontal-step))))) (insert (concat (make-string @end group @group ;; @r{Insert white space.} (- (* symbol-width X-axis-label-spacing) (1- (length (int-to-string horizontal-step))) 2) ? ) (int-to-string (* number horizontal-step)))) @end group @group ;; @r{Insert remaining numbers.} (setq number (+ number X-axis-label-spacing)) (while (> number-of-X-tics 1) (insert (X-axis-element (* number horizontal-step))) (setq number (+ number X-axis-label-spacing)) (setq number-of-X-tics (1- number-of-X-tics))))) @end group @end example If you are reading this in Info, you can see the new versions of @code{print-X-axis} @code{print-graph} and evaluate them. If you are reading this in a printed book, you can see the changed lines here (the full text is too much to print). @iftex @example @group (defun print-X-axis (numbers-list horizontal-step) @dots{} (print-X-axis-numbered-line tic-number leading-spaces horizontal-step)) @end group @end example @example @group (defun print-graph (numbers-list &optional vertical-step horizontal-step) @dots{} (print-X-axis numbers-list horizontal-step)) @end group @end example @end iftex @ifinfo @example @group (defun print-X-axis (numbers-list horizontal-step) "Print X axis labels to length of NUMBERS-LIST. Optionally, HORIZONTAL-STEP, a positive integer, specifies how much an X axis label increments for each column." @end group @group ;; Value of symbol-width and full-Y-label-width ;; are passed by `print-graph'. (let* ((leading-spaces (make-string full-Y-label-width ? )) ;; symbol-width @r{is provided by} graph-body-print (tic-width (* symbol-width X-axis-label-spacing)) (X-length (length numbers-list)) @end group @group (X-tic (concat (make-string ;; @r{Make a string of blanks.} (- (* symbol-width X-axis-label-spacing) (length X-axis-tic-symbol)) ? ) @end group @group ;; @r{Concatenate blanks with tic symbol.} X-axis-tic-symbol)) (tic-number (if (zerop (% X-length tic-width)) (/ X-length tic-width) (1+ (/ X-length tic-width))))) @end group @group (print-X-axis-tic-line tic-number leading-spaces X-tic) (insert "\n") (print-X-axis-numbered-line tic-number leading-spaces horizontal-step))) @end group @end example @example @group (defun print-graph (numbers-list &optional vertical-step horizontal-step) "Print labelled bar graph of the NUMBERS-LIST. The numbers-list consists of the Y-axis values. @end group @group Optionally, VERTICAL-STEP, a positive integer, specifies how much a Y axis label increments for each line. For example, a step of 5 means that each row is five units. @end group @group Optionally, HORIZONTAL-STEP, a positive integer, specifies how much an X axis label increments for each column." (let* ((symbol-width (length graph-blank)) ;; @code{height} @r{is both the largest number} ;; @r{and the number with the most digits.} (height (apply 'max numbers-list)) @end group @group (height-of-top-line (if (zerop (% height Y-axis-label-spacing)) height ;; @r{else} (* (1+ (/ height Y-axis-label-spacing)) Y-axis-label-spacing))) @end group @group (vertical-step (or vertical-step 1)) (full-Y-label-width (length (concat (int-to-string (* height-of-top-line vertical-step)) Y-axis-tic)))) @end group @group (print-Y-axis height-of-top-line full-Y-label-width vertical-step) (graph-body-print numbers-list height-of-top-line symbol-width) (print-X-axis numbers-list horizontal-step))) @end group @end example @end ifinfo @ignore Graphing Definitions Re-listed @need 1250 Here are all the graphing definitions in their final form: @example @group (defvar top-of-ranges '(10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250) "List specifying ranges for `defuns-per-range'.") @end group @group (defvar graph-symbol "*" "String used as symbol in graph, usually an asterisk.") @end group @group (defvar graph-blank " " "String used as blank in graph, usually a blank space. graph-blank must be the same number of columns wide as graph-symbol.") @end group @group (defvar Y-axis-tic " - " "String that follows number in a Y axis label.") @end group @group (defvar Y-axis-label-spacing 5 "Number of lines from one Y axis label to next.") @end group @group (defvar X-axis-tic-symbol "|" "String to insert to point to a column in X axis.") @end group @group (defvar X-axis-label-spacing (if (boundp 'graph-blank) (* 5 (length graph-blank)) 5) "Number of units from one X axis label to next.") @end group @end example @example @group (defun count-words-in-defun () "Return the number of words and symbols in a defun." (beginning-of-defun) (let ((count 0) (end (save-excursion (end-of-defun) (point)))) @end group @group (while (and (< (point) end) (re-search-forward "\\(\\w\\|\\s_\\)+[^ \t\n]*[ \t\n]*" end t)) (setq count (1+ count))) count)) @end group @end example @example @group (defun lengths-list-file (filename) "Return list of definitions' lengths within FILE. The returned list is a list of numbers. Each number is the number of words or symbols in one function definition." @end group @group (message "Working on `%s' ... " filename) (save-excursion (let ((buffer (find-file-noselect filename)) (lengths-list)) (set-buffer buffer) (setq buffer-read-only t) (widen) (goto-char (point-min)) @end group @group (while (re-search-forward "^(defun" nil t) (setq lengths-list (cons (count-words-in-defun) lengths-list))) (kill-buffer buffer) lengths-list))) @end group @end example @example @group (defun lengths-list-many-files (list-of-files) "Return list of lengths of defuns in LIST-OF-FILES." (let (lengths-list) ;;; @r{true-or-false-test} (while list-of-files (setq lengths-list (append lengths-list @end group @group ;;; @r{Generate a lengths' list.} (lengths-list-file (expand-file-name (car list-of-files))))) ;;; @r{Make files' list shorter.} (setq list-of-files (cdr list-of-files))) ;;; @r{Return final value of lengths' list.} lengths-list)) @end group @end example @example @group (defun defuns-per-range (sorted-lengths top-of-ranges) "SORTED-LENGTHS defuns in each TOP-OF-RANGES range." (let ((top-of-range (car top-of-ranges)) (number-within-range 0) defuns-per-range-list) @end group @group ;; @r{Outer loop.} (while top-of-ranges ;; @r{Inner loop.} (while (and ;; @r{Need number for numeric test.} (car sorted-lengths) (< (car sorted-lengths) top-of-range)) ;; @r{Count number of definitions within current range.} (setq number-within-range (1+ number-within-range)) (setq sorted-lengths (cdr sorted-lengths))) @end group @group ;; @r{Exit inner loop but remain within outer loop.} (setq defuns-per-range-list (cons number-within-range defuns-per-range-list)) (setq number-within-range 0) ; @r{Reset count to zero.} ;; @r{Move to next range.} (setq top-of-ranges (cdr top-of-ranges)) ;; @r{Specify next top of range value.} (setq top-of-range (car top-of-ranges))) @end group @group ;; @r{Exit outer loop and count the number of defuns larger than} ;; @r{ the largest top-of-range value.} (setq defuns-per-range-list (cons (length sorted-lengths) defuns-per-range-list)) ;; @r{Return a list of the number of definitions within each range,} ;; @r{ smallest to largest.} (nreverse defuns-per-range-list))) @end group @end example @example @group (defun column-of-graph (max-graph-height actual-height) "Return list of MAX-GRAPH-HEIGHT strings; ACTUAL-HEIGHT are graph-symbols. The graph-symbols are contiguous entries at the end of the list. The list will be inserted as one column of a graph. The strings are either graph-blank or graph-symbol." @end group @group (let ((insert-list nil) (number-of-top-blanks (- max-graph-height actual-height))) ;; @r{Fill in @code{graph-symbols}.} (while (> actual-height 0) (setq insert-list (cons graph-symbol insert-list)) (setq actual-height (1- actual-height))) @end group @group ;; @r{Fill in @code{graph-blanks}.} (while (> number-of-top-blanks 0) (setq insert-list (cons graph-blank insert-list)) (setq number-of-top-blanks (1- number-of-top-blanks))) ;; @r{Return whole list.} insert-list)) @end group @end example @example @group (defun Y-axis-element (number full-Y-label-width) "Construct a NUMBERed label element. A numbered element looks like this ` 5 - ', and is padded as needed so all line up with the element for the largest number." @end group @group (let* ((leading-spaces (- full-Y-label-width (length (concat (int-to-string number) Y-axis-tic))))) @end group @group (concat (make-string leading-spaces ? ) (int-to-string number) Y-axis-tic))) @end group @end example @example @group (defun print-Y-axis (height full-Y-label-width &optional vertical-step) "Insert Y axis by HEIGHT and FULL-Y-LABEL-WIDTH. Height must be the maximum height of the graph. Full width is the width of the highest label element. Optionally, print according to VERTICAL-STEP." @end group @group ;; Value of height and full-Y-label-width ;; are passed by `print-graph'. (let ((start (point))) (insert-rectangle (Y-axis-column height full-Y-label-width vertical-step)) @end group @group ;; @r{Place point ready for inserting graph.} (goto-char start) ;; @r{Move point forward by value of} full-Y-label-width (forward-char full-Y-label-width))) @end group @end example @example @group (defun print-X-axis-tic-line (number-of-X-tics X-axis-leading-spaces X-axis-tic-element) "Print tics for X axis." (insert X-axis-leading-spaces) (insert X-axis-tic-symbol) ; @r{Under first column.} @end group @group ;; @r{Insert second tic in the right spot.} (insert (concat (make-string (- (* symbol-width X-axis-label-spacing) ;; @r{Insert white space up to second tic symbol.} (* 2 (length X-axis-tic-symbol))) ? ) X-axis-tic-symbol)) @end group @group ;; @r{Insert remaining tics.} (while (> number-of-X-tics 1) (insert X-axis-tic-element) (setq number-of-X-tics (1- number-of-X-tics)))) @end group @end example @example @group (defun X-axis-element (number) "Construct a numbered X axis element." (let ((leading-spaces (- (* symbol-width X-axis-label-spacing) (length (int-to-string number))))) (concat (make-string leading-spaces ? ) (int-to-string number)))) @end group @end example @example @group (defun graph-body-print (numbers-list height symbol-width) "Print a bar graph of the NUMBERS-LIST. The numbers-list consists of the Y-axis values. HEIGHT is maximum height of graph. SYMBOL-WIDTH is number of each column." @end group @group (let (from-position) (while numbers-list (setq from-position (point)) (insert-rectangle (column-of-graph height (car numbers-list))) (goto-char from-position) (forward-char symbol-width) @end group @group ;; @r{Draw graph column by column.} (sit-for 0) (setq numbers-list (cdr numbers-list))) ;; @r{Place point for X axis labels.} (forward-line height) (insert "\n"))) @end group @end example @example @group (defun Y-axis-column (height width-of-label &optional vertical-step) "Construct list of labels for Y axis. HEIGHT is maximum height of graph. WIDTH-OF-LABEL is maximum width of label. @end group @group VERTICAL-STEP, an option, is a positive integer that specifies how much a Y axis label increments for each line. For example, a step of 5 means that each line is five units of the graph." (let (Y-axis (number-per-line (or vertical-step 1))) @end group @group (while (> height 1) (if (zerop (% height Y-axis-label-spacing)) ;; @r{Insert label.} (setq Y-axis (cons (Y-axis-element (* height number-per-line) width-of-label) Y-axis)) @end group @group ;; @r{Else, insert blanks.} (setq Y-axis (cons (make-string width-of-label ? ) Y-axis))) (setq height (1- height))) @end group @group ;; @r{Insert base line.} (setq Y-axis (cons (Y-axis-element (or vertical-step 1) width-of-label) Y-axis)) (nreverse Y-axis))) @end group @end example @example @group (defun print-X-axis-numbered-line (number-of-X-tics X-axis-leading-spaces &optional horizontal-step) "Print line of X-axis numbers" (let ((number X-axis-label-spacing) (horizontal-step (or horizontal-step 1))) @end group @group (insert X-axis-leading-spaces) ;; line up number (delete-char (- (1- (length (int-to-string horizontal-step))))) (insert (concat (make-string ;; @r{Insert white space up to next number.} (- (* symbol-width X-axis-label-spacing) (1- (length (int-to-string horizontal-step))) 2) ? ) (int-to-string (* number horizontal-step)))) @end group @group ;; @r{Insert remaining numbers.} (setq number (+ number X-axis-label-spacing)) (while (> number-of-X-tics 1) (insert (X-axis-element (* number horizontal-step))) (setq number (+ number X-axis-label-spacing)) (setq number-of-X-tics (1- number-of-X-tics))))) @end group @end example @example @group (defun print-X-axis (numbers-list horizontal-step) "Print X axis labels to length of NUMBERS-LIST. Optionally, HORIZONTAL-STEP, a positive integer, specifies how much an X axis label increments for each column." @end group @group ;; Value of symbol-width and full-Y-label-width ;; are passed by `print-graph'. (let* ((leading-spaces (make-string full-Y-label-width ? )) ;; symbol-width @r{is provided by} graph-body-print (tic-width (* symbol-width X-axis-label-spacing)) (X-length (length numbers-list)) @end group @group (X-tic (concat (make-string ;; @r{Make a string of blanks.} (- (* symbol-width X-axis-label-spacing) (length X-axis-tic-symbol)) ? ) @end group @group ;; @r{Concatenate blanks with tic symbol.} X-axis-tic-symbol)) (tic-number (if (zerop (% X-length tic-width)) (/ X-length tic-width) (1+ (/ X-length tic-width))))) @end group @group (print-X-axis-tic-line tic-number leading-spaces X-tic) (insert "\n") (print-X-axis-numbered-line tic-number leading-spaces horizontal-step))) @end group @end example @example @group (defun one-fiftieth (full-range) "Return list, each number of which is 1/50th previous." (mapcar '(lambda (arg) (/ arg 50)) full-range)) @end group @end example @example @group (defun print-graph (numbers-list &optional vertical-step horizontal-step) "Print labelled bar graph of the NUMBERS-LIST. The numbers-list consists of the Y-axis values. @end group @group Optionally, VERTICAL-STEP, a positive integer, specifies how much a Y axis label increments for each line. For example, a step of 5 means that each row is five units. @end group @group Optionally, HORIZONTAL-STEP, a positive integer, specifies how much an X axis label increments for each column." (let* ((symbol-width (length graph-blank)) ;; @code{height} @r{is both the largest number} ;; @r{and the number with the most digits.} (height (apply 'max numbers-list)) @end group @group (height-of-top-line (if (zerop (% height Y-axis-label-spacing)) height ;; @r{else} (* (1+ (/ height Y-axis-label-spacing)) Y-axis-label-spacing))) @end group @group (vertical-step (or vertical-step 1)) (full-Y-label-width (length (concat (int-to-string (* height-of-top-line vertical-step)) Y-axis-tic)))) @end group @group (print-Y-axis height-of-top-line full-Y-label-width vertical-step) (graph-body-print numbers-list height-of-top-line symbol-width) (print-X-axis numbers-list horizontal-step))) @end group @end example @end ignore @page @node Final Printed Graph, , Graphing words in defuns, Print Whole Graph @appendixsubsec The Printed Graph When made and installed, you can call the @code{print-graph} command like this: @example @group (print-graph fiftieth-list-for-graph 50 10) @end group @end example Here is the graph: @sp 2 @example @group 1000 - * ** ** ** ** 750 - *** *** *** *** **** 500 - ***** ****** ****** ****** ******* 250 - ******** ********* * *********** * ************* * 50 - ***************** * * | | | | | | | | 10 50 100 150 200 250 300 350 @end group @end example @sp 2 The largest group of functions contain 10 -- 19 words and symbols each. @node Index, About the Author, Full Graph, Top @comment node-name, next, previous, up @unnumbered Index @ifinfo MENU ENTRY: NODE NAME. @end ifinfo @printindex cp @iftex @c Place biographical information on right-hand (verso) page @tex \ifodd\pageno \par\vfill\supereject \global\evenheadline={\hfil} \global\evenfootline={\hfil} \global\oddheadline={\hfil} \global\oddfootline={\hfil} \page\hbox{}\page \else \par\vfill\supereject \par\vfill\supereject \global\evenheadline={\hfil} \global\evenfootline={\hfil} \global\oddheadline={\hfil} \global\oddfootline={\hfil} \page\hbox{}\page \page\hbox{}\page \fi @end tex @page @w{ } @c ================ Biographical information ================ @w{ } @sp 8 @center About the Author @sp 1 @end iftex @ifinfo @node About the Author, , Index, Top @unnumbered About the Author @end ifinfo @quotation Robert J. Chassell has worked with GNU Emacs since 1985. He writes and edits, teaches Emacs and Emacs Lisp, and is a director and the Secretary/Treasurer of the @w{Free Software Foundation, Inc.} He has an abiding interest in social and economic history and flies his own airplane. @end quotation @page @w{ } @c Prevent page number on blank verso, so eject it first. @tex \par\vfill\supereject @end tex @iftex @headings off @evenheading @thispage @| @| @thistitle @oddheading @| @| @thispage @end iftex @c Keep T.O.C. short by tightening up. @ifset largebook @tex \global\parskip 2pt plus 1pt \global\advance\baselineskip by -1pt @end tex @end ifset @shortcontents @contents @bye emacs-lisp-intro-1.04/lambda-diagram1.eps100644 12062 13 24014 5763657270 16272 0ustar bobuser%! %%BoundingBox: 33 710 173 759 %%Title: lambda-diagram1 %%CreationDate: Wed Mar 8 14:31:53 1995 %%Creator: Tgif-2.16-p4 by William Chia-Wei Cheng (william@cs.UCLA.edu) % % Due to bugs in Transcript, the 'PS-Adobe-' stuff is omitted from line 1 % /tgifdict 132 dict def tgifdict begin % % Using a zero value radius for an ellipse or an arc would result % in a non-invertible CTM matrix which causes problem when this % when this PostScript is wrapped inside other routines, such as % the multi.ps package from % ftp.ucc.su.oz.au:/pub/ps_printing/multi. You can overcome such % error by uncommenting the sole line of the procedure below: % /tgif_min_radius { % dup 0.01 lt { pop 0.01 } if } bind def /tgifellipsedict 6 dict def tgifellipsedict /mtrx matrix put /tgifellipse { tgifellipsedict begin /yrad exch def /xrad exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate xrad yrad scale 0 0 1 0 360 arc savematrix setmatrix end } def /tgifarrowtipdict 8 dict def tgifarrowtipdict /mtrx matrix put /tgifarrowtip { tgifarrowtipdict begin /dy exch def /dx exch def /h exch def /w exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate dy dx atan rotate 0 0 moveto w neg h lineto w neg h neg lineto savematrix setmatrix end } def /tgifarcdict 8 dict def tgifarcdict /mtrx matrix put /tgifarcn { tgifarcdict begin /endangle exch def /startangle exch def /yrad exch def /xrad exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate xrad yrad scale 0 0 1 startangle endangle arc savematrix setmatrix end } def /tgifarc { tgifarcdict begin /endangle exch def /startangle exch def /yrad exch def /xrad exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate xrad yrad scale 0 0 1 startangle endangle arcn savematrix setmatrix end } def /tgifsetuserscreendict 22 dict def tgifsetuserscreendict begin /tempctm matrix def /temprot matrix def /tempscale matrix def /concatprocs { /proc2 exch cvlit def /proc1 exch cvlit def /newproc proc1 length proc2 length add array def newproc 0 proc1 putinterval newproc proc1 length proc2 putinterval newproc cvx } def /resmatrix matrix def /findresolution { 72 0 resmatrix defaultmatrix dtransform /yres exch def /xres exch def xres dup mul yres dup mul add sqrt } def end /tgifsetuserscreen { tgifsetuserscreendict begin /spotfunction exch def /screenangle exch def /cellsize exch def /m tempctm currentmatrix def /rm screenangle temprot rotate def /sm cellsize dup tempscale scale def sm rm m m concatmatrix m concatmatrix pop 1 0 m dtransform /y1 exch def /x1 exch def /veclength x1 dup mul y1 dup mul add sqrt def /frequency findresolution veclength div def /newscreenangle y1 x1 atan def m 2 get m 1 get mul m 0 get m 3 get mul sub 0 gt {{neg} /spotfunction load concatprocs /spotfunction exch def } if frequency newscreenangle /spotfunction load setscreen end } def /tgifsetpatterndict 18 dict def tgifsetpatterndict begin /bitison { /ybit exch def /xbit exch def /bytevalue bstring ybit bwidth mul xbit 8 idiv add get def /mask 1 7 xbit 8 mod sub bitshift def bytevalue mask and 0 ne } def end /tgifbitpatternspotfunction { tgifsetpatterndict begin /y exch def /x exch def /xindex x 1 add 2 div bpside mul cvi def /yindex y 1 add 2 div bpside mul cvi def xindex yindex bitison { /onbits onbits 1 add def 1 } { /offbits offbits 1 add def 0 } ifelse end } def /tgifsetpattern { tgifsetpatterndict begin /cellsz exch def /angle exch def /bwidth exch def /bpside exch def /bstring exch def /onbits 0 def /offbits 0 def cellsz angle /tgifbitpatternspotfunction load tgifsetuserscreen {} settransfer offbits offbits onbits add div setgray end } def /tgifxpmdict 4 dict def /tgifbwpicstr 1 string def /tgifcolorpicstr 3 string def /tgifsetpixels { tgifxpmdict begin /pixels exch def end } def /tgifsetpix { tgifxpmdict begin pixels 3 1 roll putinterval end } def /tgifbwspot { tgifxpmdict begin /index exch def tgifbwpicstr 0 pixels index 3 mul 3 getinterval aload pop 255 mul .114 mul exch 255 mul .587 mul add exch 255 mul .299 mul add cvi put tgifbwpicstr end } def /tgifcolorspot { tgifxpmdict begin /index exch def pixels index 3 mul 3 getinterval aload pop 255 mul cvi tgifcolorpicstr 2 3 -1 roll put 255 mul cvi tgifcolorpicstr 1 3 -1 roll put 255 mul cvi tgifcolorpicstr 0 3 -1 roll put tgifcolorpicstr end } def /tgifnewcolorspot { tgifxpmdict begin /index exch def pixels index 3 mul 3 getinterval aload pop setrgbcolor end } def /tgifcolordict 4 dict def /colorimage where { pop } { /colorimage { tgifcolordict begin pop pop pop pop pop /ih exch def /iw exch def /x 0 def /y 0 def 1 1 ih { pop 1 1 iw { pop currentfile tgifbwpicstr readhexstring pop 0 get tgifnewcolorspot x y moveto 1 0 rlineto 0 1 rlineto -1 0 rlineto closepath fill /x x 1 add def } for /y y 1 add def /x 0 def } for end } def } ifelse /tgifpatdict 10 dict def /tgifpatbyte { currentdict /retstr get exch pat i cellsz mod get put } def /tgifpatproc { 0 1 widthlim {tgifpatbyte} for retstr /i i 1 add def } def /tgifpatfill { tgifpatdict begin /h exch def /w exch def /lty exch def /ltx exch def /cellsz exch def /pat exch def /widthlim w cellsz div cvi 1 sub def /retstr widthlim 1 add string def /i 0 def ltx lty translate w h true [1 0 0 1 0 0] {tgifpatproc} imagemask ltx neg lty neg translate end } def /pat1 def /pat2 <0000000000000000> def /pat3 <8000000008000000> def /pat4 <8800000022000000> def /pat5 <8800220088002200> def /pat6 <8822882288228822> def /pat7 def /pat8 <77dd77dd77dd77dd> def /pat9 <77ffddff77ffddff> def /pat10 <77ffffff77ffffff> def /pat11 <7fffffff7fffffff> def /pat12 <8040200002040800> def /pat13 <40a00000040a0000> def /pat14 def /pat15 def /pat16 def /pat17 <038448300c020101> def /pat18 <081c22c180010204> def /pat19 <8080413e080814e3> def /pat20 <8040201008040201> def /pat21 <8844221188442211> def /pat22 <77bbddee77bbddee> def /pat23 def /pat24 <7fbfdfeff7fbfdfe> def /pat25 <3e1f8fc7e3f1f87c> def /pat26 <0102040810204080> def /pat27 <1122448811224488> def /pat28 def /pat29 <83070e1c3870e0c1> def /pat30 def /pat31 <7cf8f1e3c78f1f3e> def /tgifcentertext { dup stringwidth pop 2 div neg 0 rmoveto } def /tgifrighttext { dup stringwidth pop neg 0 rmoveto } def /tgifreencsmalldict 12 dict def /tgifReEncodeSmall { tgifreencsmalldict begin /newcodesandnames exch def /newfontname exch def /basefontname exch def /basefontdict basefontname findfont def /newfont basefontdict maxlength dict def basefontdict { exch dup /FID ne { dup /Encoding eq { exch dup length array copy newfont 3 1 roll put } { exch newfont 3 1 roll put } ifelse } { pop pop } ifelse } forall newfont /FontName newfontname put newcodesandnames aload pop newcodesandnames length 2 idiv { newfont /Encoding get 3 1 roll put} repeat newfontname newfont definefont pop end } def /tgifgray { 8 1 0 72 300 32 div div tgifsetpattern } bind def /tgifboxdict 6 dict def /tgifboxstroke { tgifboxdict begin /pat def /w def /y2 exch def /x2 exch def /y1 exch def /x1 exch def 1.415 setmiterlimit w 1 eq { w setlinewidth } if pat pat1 ne pat pat2 ne and { gsave pat tgifgray } if newpath x1 y1 moveto x2 y1 lineto x2 y2 lineto x1 y2 lineto closepath pat pat2 eq { 1 setgray stroke 0 setgray } { stroke } ifelse pat pat1 ne pat pat2 ne and { grestore } if w 1 eq { 1 setlinewidth } if 1 setmiterlimit end } def /tgifboxfill { tgifboxdict begin /pat def /y2 exch def /x2 exch def /y1 exch def /x1 exch def pat pat1 ne pat pat2 ne and { gsave pat tgifgray } if newpath x1 y1 moveto x2 y1 lineto x2 y2 lineto x1 y2 lineto closepath pat pat2 eq { 1 setgray fill 0 setgray } { fill } ifelse pat pat1 ne pat pat2 ne and { grestore } if end } def end %%PageBoundingBox: 33 710 173 759 tgifdict begin /tgifsavedpage save def 1 setmiterlimit 1 setlinewidth 0 setgray 72 0 mul 72 11.00 mul translate 72 128 div 100 mul 100 div dup neg scale gsave % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 63 75 moveto (\(multiply-by-seven 3\)) show grestore % POLY/OPEN-SPLINE gsave newpath 80 80 moveto 96 96 lineto 224 96 lineto 240 80 lineto stroke grestore % POLY/OPEN-SPLINE gsave newpath 258 119 moveto -22 0 atan dup cos 8 mul 258 exch sub exch sin 8 mul 97 exch sub lineto stroke grestore gsave newpath 258 97 8 3 0 -22 tgifarrowtip closepath fill grestore % POLY/OPEN-SPLINE gsave newpath 160 103 moveto 160 119 lineto stroke grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 112 139 moveto (function) show grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 224 139 moveto (argument) show grestore grestore tgifsavedpage restore end %MatchingCreationDate: Wed Mar 8 14:31:53 1995 emacs-lisp-intro-1.04/lambda-diagram2.eps100644 12062 13 24046 5763657270 16300 0ustar bobuser%! %%BoundingBox: 33 730 240 777 %%Title: lambda-diagram2 %%CreationDate: Wed Mar 8 14:33:09 1995 %%Creator: Tgif-2.16-p4 by William Chia-Wei Cheng (william@cs.UCLA.edu) % % Due to bugs in Transcript, the 'PS-Adobe-' stuff is omitted from line 1 % /tgifdict 132 dict def tgifdict begin % % Using a zero value radius for an ellipse or an arc would result % in a non-invertible CTM matrix which causes problem when this % when this PostScript is wrapped inside other routines, such as % the multi.ps package from % ftp.ucc.su.oz.au:/pub/ps_printing/multi. You can overcome such % error by uncommenting the sole line of the procedure below: % /tgif_min_radius { % dup 0.01 lt { pop 0.01 } if } bind def /tgifellipsedict 6 dict def tgifellipsedict /mtrx matrix put /tgifellipse { tgifellipsedict begin /yrad exch def /xrad exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate xrad yrad scale 0 0 1 0 360 arc savematrix setmatrix end } def /tgifarrowtipdict 8 dict def tgifarrowtipdict /mtrx matrix put /tgifarrowtip { tgifarrowtipdict begin /dy exch def /dx exch def /h exch def /w exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate dy dx atan rotate 0 0 moveto w neg h lineto w neg h neg lineto savematrix setmatrix end } def /tgifarcdict 8 dict def tgifarcdict /mtrx matrix put /tgifarcn { tgifarcdict begin /endangle exch def /startangle exch def /yrad exch def /xrad exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate xrad yrad scale 0 0 1 startangle endangle arc savematrix setmatrix end } def /tgifarc { tgifarcdict begin /endangle exch def /startangle exch def /yrad exch def /xrad exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate xrad yrad scale 0 0 1 startangle endangle arcn savematrix setmatrix end } def /tgifsetuserscreendict 22 dict def tgifsetuserscreendict begin /tempctm matrix def /temprot matrix def /tempscale matrix def /concatprocs { /proc2 exch cvlit def /proc1 exch cvlit def /newproc proc1 length proc2 length add array def newproc 0 proc1 putinterval newproc proc1 length proc2 putinterval newproc cvx } def /resmatrix matrix def /findresolution { 72 0 resmatrix defaultmatrix dtransform /yres exch def /xres exch def xres dup mul yres dup mul add sqrt } def end /tgifsetuserscreen { tgifsetuserscreendict begin /spotfunction exch def /screenangle exch def /cellsize exch def /m tempctm currentmatrix def /rm screenangle temprot rotate def /sm cellsize dup tempscale scale def sm rm m m concatmatrix m concatmatrix pop 1 0 m dtransform /y1 exch def /x1 exch def /veclength x1 dup mul y1 dup mul add sqrt def /frequency findresolution veclength div def /newscreenangle y1 x1 atan def m 2 get m 1 get mul m 0 get m 3 get mul sub 0 gt {{neg} /spotfunction load concatprocs /spotfunction exch def } if frequency newscreenangle /spotfunction load setscreen end } def /tgifsetpatterndict 18 dict def tgifsetpatterndict begin /bitison { /ybit exch def /xbit exch def /bytevalue bstring ybit bwidth mul xbit 8 idiv add get def /mask 1 7 xbit 8 mod sub bitshift def bytevalue mask and 0 ne } def end /tgifbitpatternspotfunction { tgifsetpatterndict begin /y exch def /x exch def /xindex x 1 add 2 div bpside mul cvi def /yindex y 1 add 2 div bpside mul cvi def xindex yindex bitison { /onbits onbits 1 add def 1 } { /offbits offbits 1 add def 0 } ifelse end } def /tgifsetpattern { tgifsetpatterndict begin /cellsz exch def /angle exch def /bwidth exch def /bpside exch def /bstring exch def /onbits 0 def /offbits 0 def cellsz angle /tgifbitpatternspotfunction load tgifsetuserscreen {} settransfer offbits offbits onbits add div setgray end } def /tgifxpmdict 4 dict def /tgifbwpicstr 1 string def /tgifcolorpicstr 3 string def /tgifsetpixels { tgifxpmdict begin /pixels exch def end } def /tgifsetpix { tgifxpmdict begin pixels 3 1 roll putinterval end } def /tgifbwspot { tgifxpmdict begin /index exch def tgifbwpicstr 0 pixels index 3 mul 3 getinterval aload pop 255 mul .114 mul exch 255 mul .587 mul add exch 255 mul .299 mul add cvi put tgifbwpicstr end } def /tgifcolorspot { tgifxpmdict begin /index exch def pixels index 3 mul 3 getinterval aload pop 255 mul cvi tgifcolorpicstr 2 3 -1 roll put 255 mul cvi tgifcolorpicstr 1 3 -1 roll put 255 mul cvi tgifcolorpicstr 0 3 -1 roll put tgifcolorpicstr end } def /tgifnewcolorspot { tgifxpmdict begin /index exch def pixels index 3 mul 3 getinterval aload pop setrgbcolor end } def /tgifcolordict 4 dict def /colorimage where { pop } { /colorimage { tgifcolordict begin pop pop pop pop pop /ih exch def /iw exch def /x 0 def /y 0 def 1 1 ih { pop 1 1 iw { pop currentfile tgifbwpicstr readhexstring pop 0 get tgifnewcolorspot x y moveto 1 0 rlineto 0 1 rlineto -1 0 rlineto closepath fill /x x 1 add def } for /y y 1 add def /x 0 def } for end } def } ifelse /tgifpatdict 10 dict def /tgifpatbyte { currentdict /retstr get exch pat i cellsz mod get put } def /tgifpatproc { 0 1 widthlim {tgifpatbyte} for retstr /i i 1 add def } def /tgifpatfill { tgifpatdict begin /h exch def /w exch def /lty exch def /ltx exch def /cellsz exch def /pat exch def /widthlim w cellsz div cvi 1 sub def /retstr widthlim 1 add string def /i 0 def ltx lty translate w h true [1 0 0 1 0 0] {tgifpatproc} imagemask ltx neg lty neg translate end } def /pat1 def /pat2 <0000000000000000> def /pat3 <8000000008000000> def /pat4 <8800000022000000> def /pat5 <8800220088002200> def /pat6 <8822882288228822> def /pat7 def /pat8 <77dd77dd77dd77dd> def /pat9 <77ffddff77ffddff> def /pat10 <77ffffff77ffffff> def /pat11 <7fffffff7fffffff> def /pat12 <8040200002040800> def /pat13 <40a00000040a0000> def /pat14 def /pat15 def /pat16 def /pat17 <038448300c020101> def /pat18 <081c22c180010204> def /pat19 <8080413e080814e3> def /pat20 <8040201008040201> def /pat21 <8844221188442211> def /pat22 <77bbddee77bbddee> def /pat23 def /pat24 <7fbfdfeff7fbfdfe> def /pat25 <3e1f8fc7e3f1f87c> def /pat26 <0102040810204080> def /pat27 <1122448811224488> def /pat28 def /pat29 <83070e1c3870e0c1> def /pat30 def /pat31 <7cf8f1e3c78f1f3e> def /tgifcentertext { dup stringwidth pop 2 div neg 0 rmoveto } def /tgifrighttext { dup stringwidth pop neg 0 rmoveto } def /tgifreencsmalldict 12 dict def /tgifReEncodeSmall { tgifreencsmalldict begin /newcodesandnames exch def /newfontname exch def /basefontname exch def /basefontdict basefontname findfont def /newfont basefontdict maxlength dict def basefontdict { exch dup /FID ne { dup /Encoding eq { exch dup length array copy newfont 3 1 roll put } { exch newfont 3 1 roll put } ifelse } { pop pop } ifelse } forall newfont /FontName newfontname put newcodesandnames aload pop newcodesandnames length 2 idiv { newfont /Encoding get 3 1 roll put} repeat newfontname newfont definefont pop end } def /tgifgray { 8 1 0 72 300 32 div div tgifsetpattern } bind def /tgifboxdict 6 dict def /tgifboxstroke { tgifboxdict begin /pat def /w def /y2 exch def /x2 exch def /y1 exch def /x1 exch def 1.415 setmiterlimit w 1 eq { w setlinewidth } if pat pat1 ne pat pat2 ne and { gsave pat tgifgray } if newpath x1 y1 moveto x2 y1 lineto x2 y2 lineto x1 y2 lineto closepath pat pat2 eq { 1 setgray stroke 0 setgray } { stroke } ifelse pat pat1 ne pat pat2 ne and { grestore } if w 1 eq { 1 setlinewidth } if 1 setmiterlimit end } def /tgifboxfill { tgifboxdict begin /pat def /y2 exch def /x2 exch def /y1 exch def /x1 exch def pat pat1 ne pat pat2 ne and { gsave pat tgifgray } if newpath x1 y1 moveto x2 y1 lineto x2 y2 lineto x1 y2 lineto closepath pat pat2 eq { 1 setgray fill 0 setgray } { fill } ifelse pat pat1 ne pat pat2 ne and { grestore } if end } def end %%PageBoundingBox: 33 730 240 777 tgifdict begin /tgifsavedpage save def 1 setmiterlimit 1 setlinewidth 0 setgray 72 0 mul 72 11.00 mul translate 72 128 div 100 mul 100 div dup neg scale gsave % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 63 43 moveto (\(\(lambda \(number\) \(* 7 number\)\) 3\)) show grestore % POLY/OPEN-SPLINE gsave newpath 80 48 moveto 96 64 lineto 336 64 lineto 353 49 lineto stroke grestore % POLY/OPEN-SPLINE gsave newpath 379 85 moveto -21 0 atan dup cos 8 mul 379 exch sub exch sin 8 mul 64 exch sub lineto stroke grestore gsave newpath 379 64 8 3 0 -21 tgifarrowtip closepath fill grestore % POLY/OPEN-SPLINE gsave newpath 208 69 moveto 208 85 lineto stroke grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 112 102 moveto (anonymous function) show grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 344 102 moveto (argument) show grestore grestore tgifsavedpage restore end %MatchingCreationDate: Wed Mar 8 14:33:09 1995 emacs-lisp-intro-1.04/lambda-diagram3.eps100644 12062 13 24043 5763657270 16276 0ustar bobuser%! %%BoundingBox: 33 728 211 777 %%Title: lambda-diagram3 %%CreationDate: Wed Mar 8 14:33:49 1995 %%Creator: Tgif-2.16-p4 by William Chia-Wei Cheng (william@cs.UCLA.edu) % % Due to bugs in Transcript, the 'PS-Adobe-' stuff is omitted from line 1 % /tgifdict 132 dict def tgifdict begin % % Using a zero value radius for an ellipse or an arc would result % in a non-invertible CTM matrix which causes problem when this % when this PostScript is wrapped inside other routines, such as % the multi.ps package from % ftp.ucc.su.oz.au:/pub/ps_printing/multi. You can overcome such % error by uncommenting the sole line of the procedure below: % /tgif_min_radius { % dup 0.01 lt { pop 0.01 } if } bind def /tgifellipsedict 6 dict def tgifellipsedict /mtrx matrix put /tgifellipse { tgifellipsedict begin /yrad exch def /xrad exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate xrad yrad scale 0 0 1 0 360 arc savematrix setmatrix end } def /tgifarrowtipdict 8 dict def tgifarrowtipdict /mtrx matrix put /tgifarrowtip { tgifarrowtipdict begin /dy exch def /dx exch def /h exch def /w exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate dy dx atan rotate 0 0 moveto w neg h lineto w neg h neg lineto savematrix setmatrix end } def /tgifarcdict 8 dict def tgifarcdict /mtrx matrix put /tgifarcn { tgifarcdict begin /endangle exch def /startangle exch def /yrad exch def /xrad exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate xrad yrad scale 0 0 1 startangle endangle arc savematrix setmatrix end } def /tgifarc { tgifarcdict begin /endangle exch def /startangle exch def /yrad exch def /xrad exch def /y exch def /x exch def /savematrix mtrx currentmatrix def x y translate xrad yrad scale 0 0 1 startangle endangle arcn savematrix setmatrix end } def /tgifsetuserscreendict 22 dict def tgifsetuserscreendict begin /tempctm matrix def /temprot matrix def /tempscale matrix def /concatprocs { /proc2 exch cvlit def /proc1 exch cvlit def /newproc proc1 length proc2 length add array def newproc 0 proc1 putinterval newproc proc1 length proc2 putinterval newproc cvx } def /resmatrix matrix def /findresolution { 72 0 resmatrix defaultmatrix dtransform /yres exch def /xres exch def xres dup mul yres dup mul add sqrt } def end /tgifsetuserscreen { tgifsetuserscreendict begin /spotfunction exch def /screenangle exch def /cellsize exch def /m tempctm currentmatrix def /rm screenangle temprot rotate def /sm cellsize dup tempscale scale def sm rm m m concatmatrix m concatmatrix pop 1 0 m dtransform /y1 exch def /x1 exch def /veclength x1 dup mul y1 dup mul add sqrt def /frequency findresolution veclength div def /newscreenangle y1 x1 atan def m 2 get m 1 get mul m 0 get m 3 get mul sub 0 gt {{neg} /spotfunction load concatprocs /spotfunction exch def } if frequency newscreenangle /spotfunction load setscreen end } def /tgifsetpatterndict 18 dict def tgifsetpatterndict begin /bitison { /ybit exch def /xbit exch def /bytevalue bstring ybit bwidth mul xbit 8 idiv add get def /mask 1 7 xbit 8 mod sub bitshift def bytevalue mask and 0 ne } def end /tgifbitpatternspotfunction { tgifsetpatterndict begin /y exch def /x exch def /xindex x 1 add 2 div bpside mul cvi def /yindex y 1 add 2 div bpside mul cvi def xindex yindex bitison { /onbits onbits 1 add def 1 } { /offbits offbits 1 add def 0 } ifelse end } def /tgifsetpattern { tgifsetpatterndict begin /cellsz exch def /angle exch def /bwidth exch def /bpside exch def /bstring exch def /onbits 0 def /offbits 0 def cellsz angle /tgifbitpatternspotfunction load tgifsetuserscreen {} settransfer offbits offbits onbits add div setgray end } def /tgifxpmdict 4 dict def /tgifbwpicstr 1 string def /tgifcolorpicstr 3 string def /tgifsetpixels { tgifxpmdict begin /pixels exch def end } def /tgifsetpix { tgifxpmdict begin pixels 3 1 roll putinterval end } def /tgifbwspot { tgifxpmdict begin /index exch def tgifbwpicstr 0 pixels index 3 mul 3 getinterval aload pop 255 mul .114 mul exch 255 mul .587 mul add exch 255 mul .299 mul add cvi put tgifbwpicstr end } def /tgifcolorspot { tgifxpmdict begin /index exch def pixels index 3 mul 3 getinterval aload pop 255 mul cvi tgifcolorpicstr 2 3 -1 roll put 255 mul cvi tgifcolorpicstr 1 3 -1 roll put 255 mul cvi tgifcolorpicstr 0 3 -1 roll put tgifcolorpicstr end } def /tgifnewcolorspot { tgifxpmdict begin /index exch def pixels index 3 mul 3 getinterval aload pop setrgbcolor end } def /tgifcolordict 4 dict def /colorimage where { pop } { /colorimage { tgifcolordict begin pop pop pop pop pop /ih exch def /iw exch def /x 0 def /y 0 def 1 1 ih { pop 1 1 iw { pop currentfile tgifbwpicstr readhexstring pop 0 get tgifnewcolorspot x y moveto 1 0 rlineto 0 1 rlineto -1 0 rlineto closepath fill /x x 1 add def } for /y y 1 add def /x 0 def } for end } def } ifelse /tgifpatdict 10 dict def /tgifpatbyte { currentdict /retstr get exch pat i cellsz mod get put } def /tgifpatproc { 0 1 widthlim {tgifpatbyte} for retstr /i i 1 add def } def /tgifpatfill { tgifpatdict begin /h exch def /w exch def /lty exch def /ltx exch def /cellsz exch def /pat exch def /widthlim w cellsz div cvi 1 sub def /retstr widthlim 1 add string def /i 0 def ltx lty translate w h true [1 0 0 1 0 0] {tgifpatproc} imagemask ltx neg lty neg translate end } def /pat1 def /pat2 <0000000000000000> def /pat3 <8000000008000000> def /pat4 <8800000022000000> def /pat5 <8800220088002200> def /pat6 <8822882288228822> def /pat7 def /pat8 <77dd77dd77dd77dd> def /pat9 <77ffddff77ffddff> def /pat10 <77ffffff77ffffff> def /pat11 <7fffffff7fffffff> def /pat12 <8040200002040800> def /pat13 <40a00000040a0000> def /pat14 def /pat15 def /pat16 def /pat17 <038448300c020101> def /pat18 <081c22c180010204> def /pat19 <8080413e080814e3> def /pat20 <8040201008040201> def /pat21 <8844221188442211> def /pat22 <77bbddee77bbddee> def /pat23 def /pat24 <7fbfdfeff7fbfdfe> def /pat25 <3e1f8fc7e3f1f87c> def /pat26 <0102040810204080> def /pat27 <1122448811224488> def /pat28 def /pat29 <83070e1c3870e0c1> def /pat30 def /pat31 <7cf8f1e3c78f1f3e> def /tgifcentertext { dup stringwidth pop 2 div neg 0 rmoveto } def /tgifrighttext { dup stringwidth pop neg 0 rmoveto } def /tgifreencsmalldict 12 dict def /tgifReEncodeSmall { tgifreencsmalldict begin /newcodesandnames exch def /newfontname exch def /basefontname exch def /basefontdict basefontname findfont def /newfont basefontdict maxlength dict def basefontdict { exch dup /FID ne { dup /Encoding eq { exch dup length array copy newfont 3 1 roll put } { exch newfont 3 1 roll put } ifelse } { pop pop } ifelse } forall newfont /FontName newfontname put newcodesandnames aload pop newcodesandnames length 2 idiv { newfont /Encoding get 3 1 roll put} repeat newfontname newfont definefont pop end } def /tgifgray { 8 1 0 72 300 32 div div tgifsetpattern } bind def /tgifboxdict 6 dict def /tgifboxstroke { tgifboxdict begin /pat def /w def /y2 exch def /x2 exch def /y1 exch def /x1 exch def 1.415 setmiterlimit w 1 eq { w setlinewidth } if pat pat1 ne pat pat2 ne and { gsave pat tgifgray } if newpath x1 y1 moveto x2 y1 lineto x2 y2 lineto x1 y2 lineto closepath pat pat2 eq { 1 setgray stroke 0 setgray } { stroke } ifelse pat pat1 ne pat pat2 ne and { grestore } if w 1 eq { 1 setlinewidth } if 1 setmiterlimit end } def /tgifboxfill { tgifboxdict begin /pat def /y2 exch def /x2 exch def /y1 exch def /x1 exch def pat pat1 ne pat pat2 ne and { gsave pat tgifgray } if newpath x1 y1 moveto x2 y1 lineto x2 y2 lineto x1 y2 lineto closepath pat pat2 eq { 1 setgray fill 0 setgray } { fill } ifelse pat pat1 ne pat pat2 ne and { grestore } if end } def end %%PageBoundingBox: 33 728 211 777 tgifdict begin /tgifsavedpage save def 1 setmiterlimit 1 setlinewidth 0 setgray 72 0 mul 72 11.00 mul translate 72 128 div 100 mul 100 div dup neg scale gsave % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 63 43 moveto (\(\(lambda \(arg\) \(/ arg 50\)\) 100\)) show grestore % POLY/OPEN-SPLINE gsave newpath 80 48 moveto 96 64 lineto 284 64 lineto 299 48 lineto stroke grestore % POLY/OPEN-SPLINE gsave newpath 332 86 moveto -25 0 atan dup cos 8 mul 332 exch sub exch sin 8 mul 61 exch sub lineto stroke grestore gsave newpath 332 61 8 3 0 -25 tgifarrowtip closepath fill grestore % POLY/OPEN-SPLINE gsave newpath 199 70 moveto 199 86 lineto stroke grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 101 106 moveto (anonymous function) show grestore % TEXT 0 setgray /Courier findfont [17 0 0 -17 0 0] makefont setfont gsave 293 106 moveto (argument) show grestore grestore tgifsavedpage restore end %MatchingCreationDate: Wed Mar 8 14:33:49 1995