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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
f9f59935 | 3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1995, 1998 Free Software Foundation, Inc. |
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4 | @c See the file elisp.texi for copying conditions. |
5 | @setfilename ../info/tips | |
6 | @node Tips, GNU Emacs Internals, Calendar, Top | |
2323275b | 7 | @appendix Tips and Conventions |
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8 | @cindex tips |
9 | @cindex standards of coding style | |
10 | @cindex coding standards | |
11 | ||
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12 | This chapter describes no additional features of Emacs Lisp. Instead |
13 | it gives advice on making effective use of the features described in the | |
14 | previous chapters, and describes conventions Emacs Lisp programmers | |
15 | should follow. | |
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16 | |
17 | @menu | |
2323275b | 18 | * Coding Conventions:: Conventions for clean and robust programs. |
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19 | * Compilation Tips:: Making compiled code run fast. |
20 | * Documentation Tips:: Writing readable documentation strings. | |
21 | * Comment Tips:: Conventions for writing comments. | |
22 | * Library Headers:: Standard headers for library packages. | |
23 | @end menu | |
24 | ||
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25 | @node Coding Conventions |
26 | @section Emacs Lisp Coding Conventions | |
7015aca4 | 27 | |
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28 | Here are conventions that you should follow when writing Emacs Lisp |
29 | code intended for widespread use: | |
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30 | |
31 | @itemize @bullet | |
32 | @item | |
33 | Since all global variables share the same name space, and all functions | |
34 | share another name space, you should choose a short word to distinguish | |
35 | your program from other Lisp programs. Then take care to begin the | |
36 | names of all global variables, constants, and functions with the chosen | |
37 | prefix. This helps avoid name conflicts. | |
38 | ||
39 | This recommendation applies even to names for traditional Lisp | |
40 | primitives that are not primitives in Emacs Lisp---even to @code{cadr}. | |
41 | Believe it or not, there is more than one plausible way to define | |
42 | @code{cadr}. Play it safe; append your name prefix to produce a name | |
43 | like @code{foo-cadr} or @code{mylib-cadr} instead. | |
44 | ||
45 | If you write a function that you think ought to be added to Emacs under | |
46 | a certain name, such as @code{twiddle-files}, don't call it by that name | |
47 | in your program. Call it @code{mylib-twiddle-files} in your program, | |
48 | and send mail to @samp{bug-gnu-emacs@@prep.ai.mit.edu} suggesting we add | |
49 | it to Emacs. If and when we do, we can change the name easily enough. | |
50 | ||
51 | If one prefix is insufficient, your package may use two or three | |
52 | alternative common prefixes, so long as they make sense. | |
53 | ||
54 | Separate the prefix from the rest of the symbol name with a hyphen, | |
55 | @samp{-}. This will be consistent with Emacs itself and with most Emacs | |
56 | Lisp programs. | |
57 | ||
58 | @item | |
59 | It is often useful to put a call to @code{provide} in each separate | |
60 | library program, at least if there is more than one entry point to the | |
61 | program. | |
62 | ||
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63 | @item |
64 | If a file requires certain other library programs to be loaded | |
65 | beforehand, then the comments at the beginning of the file should say | |
66 | so. Also, use @code{require} to make sure they are loaded. | |
67 | ||
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68 | @item |
69 | If one file @var{foo} uses a macro defined in another file @var{bar}, | |
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70 | @var{foo} should contain this expression before the first use of the |
71 | macro: | |
72 | ||
73 | @example | |
74 | (eval-when-compile (require '@var{bar})) | |
75 | @end example | |
76 | ||
77 | @noindent | |
78 | (And @var{bar} should contain @code{(provide '@var{bar})}, to make the | |
79 | @code{require} work.) This will cause @var{bar} to be loaded when you | |
80 | byte-compile @var{foo}. Otherwise, you risk compiling @var{foo} without | |
81 | the necessary macro loaded, and that would produce compiled code that | |
82 | won't work right. @xref{Compiling Macros}. | |
83 | ||
84 | Using @code{eval-when-compile} avoids loading @var{bar} when | |
85 | the compiled version of @var{foo} is @emph{used}. | |
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86 | |
87 | @item | |
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88 | When defining a major mode, please follow the major mode |
89 | conventions. @xref{Major Mode Conventions}. | |
90 | ||
91 | @item | |
92 | When defining a minor mode, please follow the minor mode | |
93 | conventions. @xref{Minor Mode Conventions}. | |
7015aca4 | 94 | |
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95 | @item |
96 | If the purpose of a function is to tell you whether a certain condition | |
97 | is true or false, give the function a name that ends in @samp{p}. If | |
98 | the name is one word, add just @samp{p}; if the name is multiple words, | |
99 | add @samp{-p}. Examples are @code{framep} and @code{frame-live-p}. | |
100 | ||
101 | @item | |
102 | If a user option variable records a true-or-false condition, give it a | |
103 | name that ends in @samp{-flag}. | |
104 | ||
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105 | @item |
106 | Please do not define @kbd{C-c @var{letter}} as a key in your major | |
107 | modes. These sequences are reserved for users; they are the | |
f9f59935 | 108 | @strong{only} sequences reserved for users, so do not block them. |
7015aca4 | 109 | |
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110 | Instead, define sequences consisting of @kbd{C-c} followed by a control |
111 | character, a digit, or certain punctuation characters. These sequences | |
112 | are reserved for major modes. | |
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113 | |
114 | Changing all the major modes in Emacs 18 so they would follow this | |
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115 | convention was a lot of work. Abandoning this convention would make |
116 | that work go to waste, and inconvenience users. | |
117 | ||
118 | @item | |
119 | Sequences consisting of @kbd{C-c} followed by @kbd{@{}, @kbd{@}}, | |
120 | @kbd{<}, @kbd{>}, @kbd{:} or @kbd{;} are also reserved for major modes. | |
121 | ||
122 | @item | |
123 | Sequences consisting of @kbd{C-c} followed by any other punctuation | |
124 | character are allocated for minor modes. Using them in a major mode is | |
125 | not absolutely prohibited, but if you do that, the major mode binding | |
126 | may be shadowed from time to time by minor modes. | |
7015aca4 | 127 | |
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128 | @item |
129 | Function keys @key{F5} through @key{F9} without modifier keys are | |
130 | reserved for users to define. | |
131 | ||
7015aca4 | 132 | @item |
f9f59935 | 133 | Do not bind @kbd{C-h} following any prefix character (including |
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134 | @kbd{C-c}). If you don't bind @kbd{C-h}, it is automatically available |
135 | as a help character for listing the subcommands of the prefix character. | |
136 | ||
137 | @item | |
f9f59935 | 138 | Do not bind a key sequence ending in @key{ESC} except following |
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139 | another @key{ESC}. (That is, it is ok to bind a sequence ending in |
140 | @kbd{@key{ESC} @key{ESC}}.) | |
141 | ||
142 | The reason for this rule is that a non-prefix binding for @key{ESC} in | |
143 | any context prevents recognition of escape sequences as function keys in | |
144 | that context. | |
145 | ||
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146 | @item |
147 | Applications should not bind mouse events based on button 1 with the | |
148 | shift key held down. These events include @kbd{S-mouse-1}, | |
149 | @kbd{M-S-mouse-1}, @kbd{C-S-mouse-1}, and so on. They are reserved for | |
150 | users. | |
151 | ||
152 | @item | |
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153 | Special major modes used for read-only text should usually redefine |
154 | @kbd{mouse-2} and @key{RET} to trace some sort of reference in the text. | |
155 | Modes such as Dired, Info, Compilation, and Occur redefine it in this | |
156 | way. | |
4b6694ef | 157 | |
7015aca4 | 158 | @item |
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159 | When a package provides a modification of ordinary Emacs behavior, it is |
160 | good to include a command to enable and disable the feature, Provide a | |
161 | command named @code{@var{whatever}-mode} which turns the feature on or | |
162 | off, and make it autoload (@pxref{Autoload}). Design the package so | |
163 | that simply loading it has no visible effect---that should not enable | |
164 | the feature. Users will request the feature by invoking the command. | |
165 | ||
166 | @item | |
167 | It is a bad idea to define aliases for the Emacs primitives. Use the | |
168 | standard names instead. | |
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169 | |
170 | @item | |
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171 | Redefining (or advising) an Emacs primitive is discouraged. It may do |
172 | the right thing for a particular program, but there is no telling what | |
173 | other programs might break as a result. | |
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174 | |
175 | @item | |
176 | If a file does replace any of the functions or library programs of | |
177 | standard Emacs, prominent comments at the beginning of the file should | |
178 | say which functions are replaced, and how the behavior of the | |
179 | replacements differs from that of the originals. | |
180 | ||
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181 | @item |
182 | Please keep the names of your Emacs Lisp source files to 13 characters | |
183 | or less. This way, if the files are compiled, the compiled files' names | |
184 | will be 14 characters or less, which is short enough to fit on all kinds | |
185 | of Unix systems. | |
186 | ||
187 | @item | |
188 | Don't use @code{next-line} or @code{previous-line} in programs; nearly | |
189 | always, @code{forward-line} is more convenient as well as more | |
190 | predictable and robust. @xref{Text Lines}. | |
191 | ||
192 | @item | |
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193 | Don't call functions that set the mark, unless setting the mark is one |
194 | of the intended features of your program. The mark is a user-level | |
195 | feature, so it is incorrect to change the mark except to supply a value | |
196 | for the user's benefit. @xref{The Mark}. | |
7015aca4 | 197 | |
f9f59935 | 198 | In particular, don't use any of these functions: |
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199 | |
200 | @itemize @bullet | |
201 | @item | |
202 | @code{beginning-of-buffer}, @code{end-of-buffer} | |
203 | @item | |
204 | @code{replace-string}, @code{replace-regexp} | |
205 | @end itemize | |
206 | ||
207 | If you just want to move point, or replace a certain string, without any | |
208 | of the other features intended for interactive users, you can replace | |
209 | these functions with one or two lines of simple Lisp code. | |
210 | ||
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211 | @item |
212 | Use lists rather than vectors, except when there is a particular reason | |
213 | to use a vector. Lisp has more facilities for manipulating lists than | |
214 | for vectors, and working with lists is usually more convenient. | |
215 | ||
216 | Vectors are advantageous for tables that are substantial in size and are | |
217 | accessed in random order (not searched front to back), provided there is | |
218 | no need to insert or delete elements (only lists allow that). | |
219 | ||
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220 | @item |
221 | The recommended way to print a message in the echo area is with | |
222 | the @code{message} function, not @code{princ}. @xref{The Echo Area}. | |
223 | ||
224 | @item | |
225 | When you encounter an error condition, call the function @code{error} | |
226 | (or @code{signal}). The function @code{error} does not return. | |
227 | @xref{Signaling Errors}. | |
228 | ||
229 | Do not use @code{message}, @code{throw}, @code{sleep-for}, | |
230 | or @code{beep} to report errors. | |
231 | ||
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232 | @item |
233 | An error message should start with a capital letter but should not end | |
234 | with a period. | |
235 | ||
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236 | @item |
237 | Many commands that take a long time to execute display a message that | |
238 | says @samp{Operating...} when they start, and change it to | |
239 | @samp{Operating...done} when they finish. Please keep the style of | |
240 | these messages uniform: @emph{no} space around the ellipsis, and | |
241 | @emph{no} period at the end. | |
242 | ||
7015aca4 | 243 | @item |
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244 | Try to avoid using recursive edits. Instead, do what the Rmail @kbd{e} |
245 | command does: use a new local keymap that contains one command defined | |
246 | to switch back to the old local keymap. Or do what the | |
247 | @code{edit-options} command does: switch to another buffer and let the | |
248 | user switch back at will. @xref{Recursive Editing}. | |
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249 | |
250 | @item | |
251 | In some other systems there is a convention of choosing variable names | |
252 | that begin and end with @samp{*}. We don't use that convention in Emacs | |
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253 | Lisp, so please don't use it in your programs. (Emacs uses such names |
254 | only for program-generated buffers.) The users will find Emacs more | |
255 | coherent if all libraries use the same conventions. | |
7015aca4 | 256 | |
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257 | @item |
258 | Try to avoid compiler warnings about undefined free variables, by adding | |
378f6042 | 259 | @code{defvar} definitions for these variables. |
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260 | |
261 | If you bind a variable in one function, and use it or set it in another | |
262 | function, the compiler warns about the latter function unless the | |
263 | variable has a definition. But often these variables have short names, | |
264 | and it is not clean for Lisp packages to define such variables names. | |
265 | Therefore, you should rename the variable to start with the name prefix | |
266 | used for the other functions and variables in your package. | |
267 | ||
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268 | @item |
269 | Indent each function with @kbd{C-M-q} (@code{indent-sexp}) using the | |
270 | default indentation parameters. | |
271 | ||
272 | @item | |
273 | Don't make a habit of putting close-parentheses on lines by themselves; | |
274 | Lisp programmers find this disconcerting. Once in a while, when there | |
275 | is a sequence of many consecutive close-parentheses, it may make sense | |
276 | to split them in one or two significant places. | |
277 | ||
278 | @item | |
279 | Please put a copyright notice on the file if you give copies to anyone. | |
f9f59935 RS |
280 | Use a message like this one: |
281 | ||
282 | @smallexample | |
283 | ;; Copyright (C) @var{year} @var{name} | |
284 | ||
285 | ;; This program is free software; you can redistribute it and/or | |
286 | ;; modify it under the terms of the GNU General Public License as | |
287 | ;; published by the Free Software Foundation; either version 2 of | |
288 | ;; the License, or (at your option) any later version. | |
289 | ||
290 | ;; This program is distributed in the hope that it will be | |
291 | ;; useful, but WITHOUT ANY WARRANTY; without even the implied | |
292 | ;; warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR | |
293 | ;; PURPOSE. See the GNU General Public License for more details. | |
294 | ||
295 | ;; You should have received a copy of the GNU General Public | |
296 | ;; License along with this program; if not, write to the Free | |
297 | ;; Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, | |
298 | ;; MA 02111-1307 USA | |
299 | @end smallexample | |
300 | ||
301 | If you have signed papers to assign the copyright to the Foundation, | |
302 | then use @samp{Free Software Foundation, Inc.} as @var{name}. | |
303 | Otherwise, use your name. | |
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304 | @end itemize |
305 | ||
306 | @node Compilation Tips | |
307 | @section Tips for Making Compiled Code Fast | |
308 | @cindex execution speed | |
309 | @cindex speedups | |
310 | ||
311 | Here are ways of improving the execution speed of byte-compiled | |
4b6694ef | 312 | Lisp programs. |
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313 | |
314 | @itemize @bullet | |
315 | @item | |
316 | @cindex profiling | |
317 | @cindex timing programs | |
318 | @cindex @file{profile.el} | |
319 | Use the @file{profile} library to profile your program. See the file | |
320 | @file{profile.el} for instructions. | |
321 | ||
322 | @item | |
323 | Use iteration rather than recursion whenever possible. | |
324 | Function calls are slow in Emacs Lisp even when a compiled function | |
325 | is calling another compiled function. | |
326 | ||
327 | @item | |
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328 | Using the primitive list-searching functions @code{memq}, @code{member}, |
329 | @code{assq}, or @code{assoc} is even faster than explicit iteration. It | |
f9f59935 | 330 | can be worth rearranging a data structure so that one of these primitive |
bfe721d1 | 331 | search functions can be used. |
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332 | |
333 | @item | |
4b6694ef | 334 | Certain built-in functions are handled specially in byte-compiled code, |
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335 | avoiding the need for an ordinary function call. It is a good idea to |
336 | use these functions rather than alternatives. To see whether a function | |
337 | is handled specially by the compiler, examine its @code{byte-compile} | |
338 | property. If the property is non-@code{nil}, then the function is | |
339 | handled specially. | |
340 | ||
341 | For example, the following input will show you that @code{aref} is | |
342 | compiled specially (@pxref{Array Functions}) while @code{elt} is not | |
343 | (@pxref{Sequence Functions}): | |
344 | ||
4b6694ef | 345 | @example |
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346 | @group |
347 | (get 'aref 'byte-compile) | |
348 | @result{} byte-compile-two-args | |
349 | @end group | |
350 | ||
351 | @group | |
352 | (get 'elt 'byte-compile) | |
353 | @result{} nil | |
354 | @end group | |
4b6694ef | 355 | @end example |
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356 | |
357 | @item | |
358 | If calling a small function accounts for a substantial part of your | |
359 | program's running time, make the function inline. This eliminates | |
360 | the function call overhead. Since making a function inline reduces | |
361 | the flexibility of changing the program, don't do it unless it gives | |
4b6694ef | 362 | a noticeable speedup in something slow enough that users care about |
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363 | the speed. @xref{Inline Functions}. |
364 | @end itemize | |
365 | ||
366 | @node Documentation Tips | |
367 | @section Tips for Documentation Strings | |
368 | ||
369 | Here are some tips for the writing of documentation strings. | |
370 | ||
371 | @itemize @bullet | |
372 | @item | |
574efc83 | 373 | Every command, function, or variable intended for users to know about |
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374 | should have a documentation string. |
375 | ||
376 | @item | |
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377 | An internal variable or subroutine of a Lisp program might as well have |
378 | a documentation string. In earlier Emacs versions, you could save space | |
379 | by using a comment instead of a documentation string, but that is no | |
380 | longer the case. | |
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381 | |
382 | @item | |
383 | The first line of the documentation string should consist of one or two | |
574efc83 | 384 | complete sentences that stand on their own as a summary. @kbd{M-x |
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385 | apropos} displays just the first line, and if it doesn't stand on its |
386 | own, the result looks bad. In particular, start the first line with a | |
387 | capital letter and end with a period. | |
7015aca4 | 388 | |
574efc83 | 389 | The documentation string can have additional lines that expand on the |
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390 | details of how to use the function or variable. The additional lines |
391 | should be made up of complete sentences also, but they may be filled if | |
392 | that looks good. | |
393 | ||
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394 | @item |
395 | For consistency, phrase the verb in the first sentence of a | |
396 | documentation string as an infinitive with ``to'' omitted. For | |
397 | instance, use ``Return the cons of A and B.'' in preference to ``Returns | |
398 | the cons of A and B@.'' Usually it looks good to do likewise for the | |
399 | rest of the first paragraph. Subsequent paragraphs usually look better | |
400 | if they have proper subjects. | |
401 | ||
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402 | @item |
403 | Write documentation strings in the active voice, not the passive, and in | |
404 | the present tense, not the future. For instance, use ``Return a list | |
405 | containing A and B.'' instead of ``A list containing A and B will be | |
406 | returned.'' | |
407 | ||
408 | @item | |
409 | Avoid using the word ``cause'' (or its equivalents) unnecessarily. | |
410 | Instead of, ``Cause Emacs to display text in boldface,'' write just | |
411 | ``Display text in boldface.'' | |
412 | ||
413 | @item | |
414 | Do not start or end a documentation string with whitespace. | |
415 | ||
416 | @item | |
417 | Format the documentation string so that it fits in an Emacs window on an | |
574efc83 | 418 | 80-column screen. It is a good idea for most lines to be no wider than |
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419 | 60 characters. The first line can be wider if necessary to fit the |
420 | information that ought to be there. | |
421 | ||
422 | However, rather than simply filling the entire documentation string, you | |
423 | can make it much more readable by choosing line breaks with care. | |
424 | Use blank lines between topics if the documentation string is long. | |
425 | ||
426 | @item | |
427 | @strong{Do not} indent subsequent lines of a documentation string so | |
428 | that the text is lined up in the source code with the text of the first | |
429 | line. This looks nice in the source code, but looks bizarre when users | |
430 | view the documentation. Remember that the indentation before the | |
431 | starting double-quote is not part of the string! | |
432 | ||
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433 | @item |
434 | When the user tries to use a disabled command, Emacs displays just the | |
435 | first paragraph of its documentation string---everything through the | |
436 | first blank line. If you wish, you can choose which information to | |
437 | include before the first blank line so as to make this display useful. | |
438 | ||
7015aca4 RS |
439 | @item |
440 | A variable's documentation string should start with @samp{*} if the | |
4b6694ef | 441 | variable is one that users would often want to set interactively. If |
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442 | the value is a long list, or a function, or if the variable would be set |
443 | only in init files, then don't start the documentation string with | |
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444 | @samp{*}. @xref{Defining Variables}. |
445 | ||
446 | @item | |
447 | The documentation string for a variable that is a yes-or-no flag should | |
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448 | start with words such as ``Non-nil means@dots{}'', to make it clear that |
449 | all non-@code{nil} values are equivalent and indicate explicitly what | |
450 | @code{nil} and non-@code{nil} mean. | |
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451 | |
452 | @item | |
453 | When a function's documentation string mentions the value of an argument | |
454 | of the function, use the argument name in capital letters as if it were | |
455 | a name for that value. Thus, the documentation string of the function | |
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456 | @code{/} refers to its second argument as @samp{DIVISOR}, because the |
457 | actual argument name is @code{divisor}. | |
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458 | |
459 | Also use all caps for meta-syntactic variables, such as when you show | |
460 | the decomposition of a list or vector into subunits, some of which may | |
461 | vary. | |
462 | ||
463 | @item | |
464 | @iftex | |
465 | When a documentation string refers to a Lisp symbol, write it as it | |
466 | would be printed (which usually means in lower case), with single-quotes | |
467 | around it. For example: @samp{`lambda'}. There are two exceptions: | |
468 | write @code{t} and @code{nil} without single-quotes. | |
469 | @end iftex | |
470 | @ifinfo | |
471 | When a documentation string refers to a Lisp symbol, write it as it | |
472 | would be printed (which usually means in lower case), with single-quotes | |
473 | around it. For example: @samp{lambda}. There are two exceptions: write | |
474 | t and nil without single-quotes. (In this manual, we normally do use | |
475 | single-quotes for those symbols.) | |
476 | @end ifinfo | |
477 | ||
478 | @item | |
479 | Don't write key sequences directly in documentation strings. Instead, | |
480 | use the @samp{\\[@dots{}]} construct to stand for them. For example, | |
9e2b495b RS |
481 | instead of writing @samp{C-f}, write the construct |
482 | @samp{\\[forward-char]}. When Emacs displays the documentation string, | |
483 | it substitutes whatever key is currently bound to @code{forward-char}. | |
484 | (This is normally @samp{C-f}, but it may be some other character if the | |
485 | user has moved key bindings.) @xref{Keys in Documentation}. | |
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486 | |
487 | @item | |
488 | In documentation strings for a major mode, you will want to refer to the | |
489 | key bindings of that mode's local map, rather than global ones. | |
490 | Therefore, use the construct @samp{\\<@dots{}>} once in the | |
491 | documentation string to specify which key map to use. Do this before | |
492 | the first use of @samp{\\[@dots{}]}. The text inside the | |
493 | @samp{\\<@dots{}>} should be the name of the variable containing the | |
494 | local keymap for the major mode. | |
495 | ||
496 | It is not practical to use @samp{\\[@dots{}]} very many times, because | |
497 | display of the documentation string will become slow. So use this to | |
498 | describe the most important commands in your major mode, and then use | |
499 | @samp{\\@{@dots{}@}} to display the rest of the mode's keymap. | |
7015aca4 RS |
500 | @end itemize |
501 | ||
502 | @node Comment Tips | |
503 | @section Tips on Writing Comments | |
504 | ||
505 | We recommend these conventions for where to put comments and how to | |
506 | indent them: | |
507 | ||
508 | @table @samp | |
509 | @item ; | |
510 | Comments that start with a single semicolon, @samp{;}, should all be | |
511 | aligned to the same column on the right of the source code. Such | |
512 | comments usually explain how the code on the same line does its job. In | |
513 | Lisp mode and related modes, the @kbd{M-;} (@code{indent-for-comment}) | |
514 | command automatically inserts such a @samp{;} in the right place, or | |
4b6694ef | 515 | aligns such a comment if it is already present. |
7015aca4 | 516 | |
574efc83 | 517 | This and following examples are taken from the Emacs sources. |
7015aca4 RS |
518 | |
519 | @smallexample | |
520 | @group | |
521 | (setq base-version-list ; there was a base | |
522 | (assoc (substring fn 0 start-vn) ; version to which | |
523 | file-version-assoc-list)) ; this looks like | |
524 | ; a subversion | |
525 | @end group | |
526 | @end smallexample | |
527 | ||
528 | @item ;; | |
529 | Comments that start with two semicolons, @samp{;;}, should be aligned to | |
4b6694ef | 530 | the same level of indentation as the code. Such comments usually |
7015aca4 RS |
531 | describe the purpose of the following lines or the state of the program |
532 | at that point. For example: | |
533 | ||
534 | @smallexample | |
535 | @group | |
536 | (prog1 (setq auto-fill-function | |
537 | @dots{} | |
538 | @dots{} | |
4b6694ef | 539 | ;; update mode line |
7015aca4 RS |
540 | (force-mode-line-update))) |
541 | @end group | |
542 | @end smallexample | |
543 | ||
4b6694ef RS |
544 | Every function that has no documentation string (because it is use only |
545 | internally within the package it belongs to), should have instead a | |
546 | two-semicolon comment right before the function, explaining what the | |
547 | function does and how to call it properly. Explain precisely what each | |
574efc83 | 548 | argument means and how the function interprets its possible values. |
7015aca4 RS |
549 | |
550 | @item ;;; | |
551 | Comments that start with three semicolons, @samp{;;;}, should start at | |
4b6694ef RS |
552 | the left margin. Such comments are used outside function definitions to |
553 | make general statements explaining the design principles of the program. | |
554 | For example: | |
7015aca4 RS |
555 | |
556 | @smallexample | |
557 | @group | |
558 | ;;; This Lisp code is run in Emacs | |
559 | ;;; when it is to operate as a server | |
560 | ;;; for other processes. | |
561 | @end group | |
562 | @end smallexample | |
563 | ||
574efc83 | 564 | Another use for triple-semicolon comments is for commenting out lines |
4b6694ef RS |
565 | within a function. We use triple-semicolons for this precisely so that |
566 | they remain at the left margin. | |
567 | ||
568 | @smallexample | |
569 | (defun foo (a) | |
570 | ;;; This is no longer necessary. | |
571 | ;;; (force-mode-line-update) | |
572 | (message "Finished with %s" a)) | |
573 | @end smallexample | |
574 | ||
7015aca4 RS |
575 | @item ;;;; |
576 | Comments that start with four semicolons, @samp{;;;;}, should be aligned | |
577 | to the left margin and are used for headings of major sections of a | |
578 | program. For example: | |
579 | ||
580 | @smallexample | |
581 | ;;;; The kill ring | |
582 | @end smallexample | |
583 | @end table | |
584 | ||
585 | @noindent | |
586 | The indentation commands of the Lisp modes in Emacs, such as @kbd{M-;} | |
587 | (@code{indent-for-comment}) and @key{TAB} (@code{lisp-indent-line}) | |
588 | automatically indent comments according to these conventions, | |
574efc83 | 589 | depending on the number of semicolons. @xref{Comments,, |
7015aca4 RS |
590 | Manipulating Comments, emacs, The GNU Emacs Manual}. |
591 | ||
7015aca4 RS |
592 | @node Library Headers |
593 | @section Conventional Headers for Emacs Libraries | |
594 | @cindex header comments | |
595 | @cindex library header comments | |
596 | ||
f9f59935 | 597 | Emacs has conventions for using special comments in Lisp libraries |
7015aca4 RS |
598 | to divide them into sections and give information such as who wrote |
599 | them. This section explains these conventions. First, an example: | |
600 | ||
601 | @smallexample | |
602 | @group | |
603 | ;;; lisp-mnt.el --- minor mode for Emacs Lisp maintainers | |
604 | ||
605 | ;; Copyright (C) 1992 Free Software Foundation, Inc. | |
606 | @end group | |
607 | ||
608 | ;; Author: Eric S. Raymond <esr@@snark.thyrsus.com> | |
609 | ;; Maintainer: Eric S. Raymond <esr@@snark.thyrsus.com> | |
610 | ;; Created: 14 Jul 1992 | |
611 | ;; Version: 1.2 | |
612 | @group | |
613 | ;; Keywords: docs | |
614 | ||
615 | ;; This file is part of GNU Emacs. | |
574efc83 | 616 | @var{copying permissions}@dots{} |
7015aca4 RS |
617 | @end group |
618 | @end smallexample | |
619 | ||
620 | The very first line should have this format: | |
621 | ||
622 | @example | |
623 | ;;; @var{filename} --- @var{description} | |
624 | @end example | |
625 | ||
626 | @noindent | |
627 | The description should be complete in one line. | |
628 | ||
629 | After the copyright notice come several @dfn{header comment} lines, | |
4b6694ef | 630 | each beginning with @samp{;; @var{header-name}:}. Here is a table of |
7015aca4 RS |
631 | the conventional possibilities for @var{header-name}: |
632 | ||
633 | @table @samp | |
634 | @item Author | |
635 | This line states the name and net address of at least the principal | |
636 | author of the library. | |
637 | ||
638 | If there are multiple authors, you can list them on continuation lines | |
4b6694ef | 639 | led by @code{;;} and a tab character, like this: |
7015aca4 RS |
640 | |
641 | @smallexample | |
642 | @group | |
643 | ;; Author: Ashwin Ram <Ram-Ashwin@@cs.yale.edu> | |
4b6694ef RS |
644 | ;; Dave Sill <de5@@ornl.gov> |
645 | ;; Dave Brennan <brennan@@hal.com> | |
646 | ;; Eric Raymond <esr@@snark.thyrsus.com> | |
7015aca4 RS |
647 | @end group |
648 | @end smallexample | |
649 | ||
650 | @item Maintainer | |
651 | This line should contain a single name/address as in the Author line, or | |
4b6694ef RS |
652 | an address only, or the string @samp{FSF}. If there is no maintainer |
653 | line, the person(s) in the Author field are presumed to be the | |
654 | maintainers. The example above is mildly bogus because the maintainer | |
655 | line is redundant. | |
7015aca4 RS |
656 | |
657 | The idea behind the @samp{Author} and @samp{Maintainer} lines is to make | |
658 | possible a Lisp function to ``send mail to the maintainer'' without | |
659 | having to mine the name out by hand. | |
660 | ||
661 | Be sure to surround the network address with @samp{<@dots{}>} if | |
662 | you include the person's full name as well as the network address. | |
663 | ||
664 | @item Created | |
665 | This optional line gives the original creation date of the | |
666 | file. For historical interest only. | |
667 | ||
668 | @item Version | |
669 | If you wish to record version numbers for the individual Lisp program, put | |
670 | them in this line. | |
671 | ||
672 | @item Adapted-By | |
673 | In this header line, place the name of the person who adapted the | |
674 | library for installation (to make it fit the style conventions, for | |
675 | example). | |
676 | ||
677 | @item Keywords | |
678 | This line lists keywords for the @code{finder-by-keyword} help command. | |
679 | This field is important; it's how people will find your package when | |
2c62739d RS |
680 | they're looking for things by topic area. To separate the keywords, you |
681 | can use spaces, commas, or both. | |
7015aca4 RS |
682 | @end table |
683 | ||
684 | Just about every Lisp library ought to have the @samp{Author} and | |
685 | @samp{Keywords} header comment lines. Use the others if they are | |
686 | appropriate. You can also put in header lines with other header | |
687 | names---they have no standard meanings, so they can't do any harm. | |
688 | ||
689 | We use additional stylized comments to subdivide the contents of the | |
690 | library file. Here is a table of them: | |
691 | ||
692 | @table @samp | |
693 | @item ;;; Commentary: | |
694 | This begins introductory comments that explain how the library works. | |
695 | It should come right after the copying permissions. | |
696 | ||
697 | @item ;;; Change log: | |
698 | This begins change log information stored in the library file (if you | |
699 | store the change history there). For most of the Lisp | |
700 | files distributed with Emacs, the change history is kept in the file | |
701 | @file{ChangeLog} and not in the source file at all; these files do | |
702 | not have a @samp{;;; Change log:} line. | |
703 | ||
704 | @item ;;; Code: | |
705 | This begins the actual code of the program. | |
706 | ||
707 | @item ;;; @var{filename} ends here | |
708 | This is the @dfn{footer line}; it appears at the very end of the file. | |
709 | Its purpose is to enable people to detect truncated versions of the file | |
710 | from the lack of a footer line. | |
711 | @end table |