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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
651f374c | 3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1995, 1998, 1999, 2002, 2003, |
ceb4c4d3 | 4 | @c 2004, 2005, 2006 Free Software Foundation, Inc. |
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5 | @c See the file elisp.texi for copying conditions. |
6 | @setfilename ../info/tips | |
e23a63a5 | 7 | @node Tips, GNU Emacs Internals, GPL, Top |
2323275b | 8 | @appendix Tips and Conventions |
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9 | @cindex tips |
10 | @cindex standards of coding style | |
11 | @cindex coding standards | |
12 | ||
2323275b RS |
13 | This chapter describes no additional features of Emacs Lisp. Instead |
14 | it gives advice on making effective use of the features described in the | |
15 | previous chapters, and describes conventions Emacs Lisp programmers | |
16 | should follow. | |
7015aca4 | 17 | |
8241495d RS |
18 | You can automatically check some of the conventions described below by |
19 | running the command @kbd{M-x checkdoc RET} when visiting a Lisp file. | |
20 | It cannot check all of the conventions, and not all the warnings it | |
21 | gives necessarily correspond to problems, but it is worth examining them | |
22 | all. | |
23 | ||
7015aca4 | 24 | @menu |
2323275b | 25 | * Coding Conventions:: Conventions for clean and robust programs. |
5e0fc18a RS |
26 | * Key Binding Conventions:: Which keys should be bound by which programs. |
27 | * Programming Tips:: Making Emacs code fit smoothly in Emacs. | |
7015aca4 | 28 | * Compilation Tips:: Making compiled code run fast. |
5e0fc18a | 29 | * Warning Tips:: Turning off compiler warnings. |
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30 | * Documentation Tips:: Writing readable documentation strings. |
31 | * Comment Tips:: Conventions for writing comments. | |
32 | * Library Headers:: Standard headers for library packages. | |
33 | @end menu | |
34 | ||
2323275b RS |
35 | @node Coding Conventions |
36 | @section Emacs Lisp Coding Conventions | |
7015aca4 | 37 | |
2323275b RS |
38 | Here are conventions that you should follow when writing Emacs Lisp |
39 | code intended for widespread use: | |
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40 | |
41 | @itemize @bullet | |
424402ec RS |
42 | @item |
43 | Simply loading the package should not change Emacs's editing behavior. | |
44 | Include a command or commands to enable and disable the feature, | |
45 | or to invoke it. | |
46 | ||
47 | This convention is mandatory for any file that includes custom | |
48 | definitions. If fixing such a file to follow this convention requires | |
49 | an incompatible change, go ahead and make the incompatible change; | |
50 | don't postpone it. | |
51 | ||
7015aca4 | 52 | @item |
92204c92 RS |
53 | Since all global variables share the same name space, and all |
54 | functions share another name space, you should choose a short word to | |
55 | distinguish your program from other Lisp programs.@footnote{The | |
56 | benefits of a Common Lisp-style package system are considered not to | |
57 | outweigh the costs.} Then take care to begin the names of all global | |
58 | variables, constants, and functions in your program with the chosen | |
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59 | prefix. This helps avoid name conflicts. (Occasionally, for a command |
60 | name intended for users to use, it is cleaner if some words come | |
61 | before the package name prefix.) | |
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62 | |
63 | This recommendation applies even to names for traditional Lisp | |
378d0f8e | 64 | primitives that are not primitives in Emacs Lisp---such as |
969fe9b5 RS |
65 | @code{copy-list}. Believe it or not, there is more than one plausible |
66 | way to define @code{copy-list}. Play it safe; append your name prefix | |
67 | to produce a name like @code{foo-copy-list} or @code{mylib-copy-list} | |
68 | instead. | |
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69 | |
70 | If you write a function that you think ought to be added to Emacs under | |
71 | a certain name, such as @code{twiddle-files}, don't call it by that name | |
72 | in your program. Call it @code{mylib-twiddle-files} in your program, | |
a9f0a989 | 73 | and send mail to @samp{bug-gnu-emacs@@gnu.org} suggesting we add |
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74 | it to Emacs. If and when we do, we can change the name easily enough. |
75 | ||
5e0fc18a | 76 | If one prefix is insufficient, your package can use two or three |
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77 | alternative common prefixes, so long as they make sense. |
78 | ||
79 | Separate the prefix from the rest of the symbol name with a hyphen, | |
80 | @samp{-}. This will be consistent with Emacs itself and with most Emacs | |
81 | Lisp programs. | |
82 | ||
83 | @item | |
5e0fc18a | 84 | Put a call to @code{provide} at the end of each separate Lisp file. |
7015aca4 | 85 | |
bfe721d1 | 86 | @item |
5e0fc18a | 87 | If a file requires certain other Lisp programs to be loaded |
bfe721d1 KH |
88 | beforehand, then the comments at the beginning of the file should say |
89 | so. Also, use @code{require} to make sure they are loaded. | |
90 | ||
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91 | @item |
92 | If one file @var{foo} uses a macro defined in another file @var{bar}, | |
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93 | @var{foo} should contain this expression before the first use of the |
94 | macro: | |
95 | ||
96 | @example | |
97 | (eval-when-compile (require '@var{bar})) | |
98 | @end example | |
99 | ||
100 | @noindent | |
969fe9b5 RS |
101 | (And the library @var{bar} should contain @code{(provide '@var{bar})}, |
102 | to make the @code{require} work.) This will cause @var{bar} to be | |
103 | loaded when you byte-compile @var{foo}. Otherwise, you risk compiling | |
104 | @var{foo} without the necessary macro loaded, and that would produce | |
105 | compiled code that won't work right. @xref{Compiling Macros}. | |
bfe721d1 KH |
106 | |
107 | Using @code{eval-when-compile} avoids loading @var{bar} when | |
108 | the compiled version of @var{foo} is @emph{used}. | |
7015aca4 | 109 | |
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110 | @item |
111 | Please don't require the @code{cl} package of Common Lisp extensions at | |
112 | run time. Use of this package is optional, and it is not part of the | |
113 | standard Emacs namespace. If your package loads @code{cl} at run time, | |
114 | that could cause name clashes for users who don't use that package. | |
115 | ||
116 | However, there is no problem with using the @code{cl} package at compile | |
378d0f8e | 117 | time, with @code{(eval-when-compile (require 'cl))}. |
becd5943 | 118 | |
7015aca4 | 119 | @item |
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120 | When defining a major mode, please follow the major mode |
121 | conventions. @xref{Major Mode Conventions}. | |
122 | ||
123 | @item | |
124 | When defining a minor mode, please follow the minor mode | |
125 | conventions. @xref{Minor Mode Conventions}. | |
7015aca4 | 126 | |
6cbf476c RS |
127 | @item |
128 | If the purpose of a function is to tell you whether a certain condition | |
129 | is true or false, give the function a name that ends in @samp{p}. If | |
130 | the name is one word, add just @samp{p}; if the name is multiple words, | |
131 | add @samp{-p}. Examples are @code{framep} and @code{frame-live-p}. | |
132 | ||
133 | @item | |
134 | If a user option variable records a true-or-false condition, give it a | |
135 | name that ends in @samp{-flag}. | |
136 | ||
49247521 LK |
137 | @item |
138 | If the purpose of a variable is to store a single function, give it a | |
139 | name that ends in @samp{-function}. If the purpose of a variable is | |
140 | to store a list of functions (i.e., the variable is a hook), please | |
141 | follow the naming conventions for hooks. @xref{Hooks}. | |
142 | ||
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143 | @item |
144 | @cindex unloading packages | |
145 | If loading the file adds functions to hooks, define a function | |
146 | @code{@var{feature}-unload-hook}, where @var{feature} is the name of | |
147 | the feature the package provides, and make it undo any such changes. | |
148 | Using @code{unload-feature} to unload the file will run this function. | |
149 | @xref{Unloading}. | |
150 | ||
151 | @item | |
152 | It is a bad idea to define aliases for the Emacs primitives. Normally | |
153 | you should use the standard names instead. The case where an alias | |
154 | may be useful is where it facilitates backwards compatibility or | |
155 | portability. | |
156 | ||
157 | @item | |
158 | If a package needs to define an alias or a new function for | |
159 | compatibility with some other version of Emacs, name it with the package | |
160 | prefix, not with the raw name with which it occurs in the other version. | |
161 | Here is an example from Gnus, which provides many examples of such | |
162 | compatibility issues. | |
163 | ||
164 | @example | |
165 | (defalias 'gnus-point-at-bol | |
166 | (if (fboundp 'point-at-bol) | |
167 | 'point-at-bol | |
168 | 'line-beginning-position)) | |
169 | @end example | |
170 | ||
171 | @item | |
172 | Redefining (or advising) an Emacs primitive is discouraged. It may do | |
173 | the right thing for a particular program, but there is no telling what | |
174 | other programs might break as a result. | |
175 | ||
176 | @item | |
177 | If a file does replace any of the functions or library programs of | |
178 | standard Emacs, prominent comments at the beginning of the file should | |
179 | say which functions are replaced, and how the behavior of the | |
180 | replacements differs from that of the originals. | |
181 | ||
182 | @item | |
183 | Avoid using macros that define functions and variables with names that | |
184 | are constructed. It is best for maintenance when the name of the | |
185 | function or variable being defined is given explicitly in the source | |
186 | code, as the second element of the list---as it is when you use | |
187 | @code{defun}, @code{defalias}, @code{defvar} and @code{defcustom}. | |
188 | ||
189 | @item | |
190 | Please keep the names of your Emacs Lisp source files to 13 characters | |
191 | or less. This way, if the files are compiled, the compiled files' names | |
192 | will be 14 characters or less, which is short enough to fit on all kinds | |
193 | of Unix systems. | |
194 | ||
195 | @item | |
196 | In some other systems there is a convention of choosing variable names | |
197 | that begin and end with @samp{*}. We don't use that convention in Emacs | |
198 | Lisp, so please don't use it in your programs. (Emacs uses such names | |
199 | only for special-purpose buffers.) The users will find Emacs more | |
200 | coherent if all libraries use the same conventions. | |
201 | ||
202 | @item | |
203 | Indent each function with @kbd{C-M-q} (@code{indent-sexp}) using the | |
204 | default indentation parameters. | |
205 | ||
206 | @item | |
207 | Don't make a habit of putting close-parentheses on lines by themselves; | |
208 | Lisp programmers find this disconcerting. Once in a while, when there | |
209 | is a sequence of many consecutive close-parentheses, it may make sense | |
210 | to split the sequence in one or two significant places. | |
211 | ||
212 | @item | |
213 | Please put a copyright notice and copying permission notice on the | |
214 | file if you distribute copies. Use a notice like this one: | |
215 | ||
216 | @smallexample | |
217 | ;; Copyright (C) @var{year} @var{name} | |
218 | ||
219 | ;; This program is free software; you can redistribute it and/or | |
220 | ;; modify it under the terms of the GNU General Public License as | |
221 | ;; published by the Free Software Foundation; either version 2 of | |
222 | ;; the License, or (at your option) any later version. | |
223 | ||
224 | ;; This program is distributed in the hope that it will be | |
225 | ;; useful, but WITHOUT ANY WARRANTY; without even the implied | |
226 | ;; warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR | |
227 | ;; PURPOSE. See the GNU General Public License for more details. | |
228 | ||
229 | ;; You should have received a copy of the GNU General Public | |
230 | ;; License along with this program; if not, write to the Free | |
231 | ;; Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, | |
232 | ;; MA 02110-1301 USA | |
233 | @end smallexample | |
234 | ||
235 | If you have signed papers to assign the copyright to the Foundation, | |
236 | then use @samp{Free Software Foundation, Inc.} as @var{name}. | |
237 | Otherwise, use your name. See also @xref{Library Headers}. | |
238 | @end itemize | |
239 | ||
240 | @node Key Binding Conventions | |
241 | @section Key Binding Conventions | |
242 | ||
243 | @itemize @bullet | |
244 | @item | |
245 | @cindex mouse-2 | |
246 | @cindex references, following | |
247 | Special major modes used for read-only text should usually redefine | |
248 | @kbd{mouse-2} and @key{RET} to trace some sort of reference in the text. | |
249 | Modes such as Dired, Info, Compilation, and Occur redefine it in this | |
250 | way. | |
251 | ||
252 | In addition, they should mark the text as a kind of ``link'' so that | |
253 | @kbd{mouse-1} will follow it also. @xref{Links and Mouse-1}. | |
254 | ||
7015aca4 | 255 | @item |
a9f0a989 RS |
256 | @cindex reserved keys |
257 | @cindex keys, reserved | |
378d0f8e RS |
258 | Please do not define @kbd{C-c @var{letter}} as a key in Lisp programs. |
259 | Sequences consisting of @kbd{C-c} and a letter (either upper or lower | |
260 | case) are reserved for users; they are the @strong{only} sequences | |
261 | reserved for users, so do not block them. | |
7015aca4 | 262 | |
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263 | Changing all the Emacs major modes to respect this convention was a |
264 | lot of work; abandoning this convention would make that work go to | |
265 | waste, and inconvenience users. Please comply with it. | |
7015aca4 | 266 | |
378d0f8e RS |
267 | @item |
268 | Function keys @key{F5} through @key{F9} without modifier keys are | |
269 | also reserved for users to define. | |
270 | ||
271 | @item | |
272 | Applications should not bind mouse events based on button 1 with the | |
273 | shift key held down. These events include @kbd{S-mouse-1}, | |
274 | @kbd{M-S-mouse-1}, @kbd{C-S-mouse-1}, and so on. They are reserved for | |
275 | users. | |
276 | ||
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277 | @item |
278 | Sequences consisting of @kbd{C-c} followed by a control character or a | |
279 | digit are reserved for major modes. | |
00d96ada RS |
280 | |
281 | @item | |
282 | Sequences consisting of @kbd{C-c} followed by @kbd{@{}, @kbd{@}}, | |
283 | @kbd{<}, @kbd{>}, @kbd{:} or @kbd{;} are also reserved for major modes. | |
284 | ||
285 | @item | |
286 | Sequences consisting of @kbd{C-c} followed by any other punctuation | |
287 | character are allocated for minor modes. Using them in a major mode is | |
288 | not absolutely prohibited, but if you do that, the major mode binding | |
289 | may be shadowed from time to time by minor modes. | |
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290 | |
291 | @item | |
f9f59935 | 292 | Do not bind @kbd{C-h} following any prefix character (including |
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293 | @kbd{C-c}). If you don't bind @kbd{C-h}, it is automatically available |
294 | as a help character for listing the subcommands of the prefix character. | |
295 | ||
296 | @item | |
f9f59935 | 297 | Do not bind a key sequence ending in @key{ESC} except following |
969fe9b5 | 298 | another @key{ESC}. (That is, it is OK to bind a sequence ending in |
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299 | @kbd{@key{ESC} @key{ESC}}.) |
300 | ||
301 | The reason for this rule is that a non-prefix binding for @key{ESC} in | |
302 | any context prevents recognition of escape sequences as function keys in | |
303 | that context. | |
304 | ||
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305 | @item |
306 | Anything which acts like a temporary mode or state which the user can | |
b6ae404e | 307 | enter and leave should define @kbd{@key{ESC} @key{ESC}} or |
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308 | @kbd{@key{ESC} @key{ESC} @key{ESC}} as a way to escape. |
309 | ||
310 | For a state which accepts ordinary Emacs commands, or more generally any | |
311 | kind of state in which @key{ESC} followed by a function key or arrow key | |
312 | is potentially meaningful, then you must not define @kbd{@key{ESC} | |
313 | @key{ESC}}, since that would preclude recognizing an escape sequence | |
314 | after @key{ESC}. In these states, you should define @kbd{@key{ESC} | |
315 | @key{ESC} @key{ESC}} as the way to escape. Otherwise, define | |
316 | @kbd{@key{ESC} @key{ESC}} instead. | |
5e0fc18a | 317 | @end itemize |
52c90d84 | 318 | |
5e0fc18a RS |
319 | @node Programming Tips |
320 | @section Emacs Programming Tips | |
3ff91798 | 321 | |
5e0fc18a RS |
322 | Following these conventions will make your program fit better |
323 | into Emacs when it runs. | |
7015aca4 | 324 | |
5e0fc18a | 325 | @itemize @bullet |
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326 | @item |
327 | Don't use @code{next-line} or @code{previous-line} in programs; nearly | |
328 | always, @code{forward-line} is more convenient as well as more | |
329 | predictable and robust. @xref{Text Lines}. | |
330 | ||
331 | @item | |
574efc83 RS |
332 | Don't call functions that set the mark, unless setting the mark is one |
333 | of the intended features of your program. The mark is a user-level | |
334 | feature, so it is incorrect to change the mark except to supply a value | |
335 | for the user's benefit. @xref{The Mark}. | |
7015aca4 | 336 | |
f9f59935 | 337 | In particular, don't use any of these functions: |
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338 | |
339 | @itemize @bullet | |
340 | @item | |
341 | @code{beginning-of-buffer}, @code{end-of-buffer} | |
342 | @item | |
343 | @code{replace-string}, @code{replace-regexp} | |
5e0fc18a RS |
344 | @item |
345 | @code{insert-file}, @code{insert-buffer} | |
7015aca4 RS |
346 | @end itemize |
347 | ||
5e0fc18a RS |
348 | If you just want to move point, or replace a certain string, or insert |
349 | a file or buffer's contents, without any of the other features | |
350 | intended for interactive users, you can replace these functions with | |
351 | one or two lines of simple Lisp code. | |
7015aca4 | 352 | |
1c2b5877 RS |
353 | @item |
354 | Use lists rather than vectors, except when there is a particular reason | |
355 | to use a vector. Lisp has more facilities for manipulating lists than | |
356 | for vectors, and working with lists is usually more convenient. | |
357 | ||
358 | Vectors are advantageous for tables that are substantial in size and are | |
359 | accessed in random order (not searched front to back), provided there is | |
360 | no need to insert or delete elements (only lists allow that). | |
361 | ||
7015aca4 | 362 | @item |
fb5a74cd | 363 | The recommended way to show a message in the echo area is with |
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364 | the @code{message} function, not @code{princ}. @xref{The Echo Area}. |
365 | ||
366 | @item | |
367 | When you encounter an error condition, call the function @code{error} | |
368 | (or @code{signal}). The function @code{error} does not return. | |
369 | @xref{Signaling Errors}. | |
370 | ||
371 | Do not use @code{message}, @code{throw}, @code{sleep-for}, | |
372 | or @code{beep} to report errors. | |
373 | ||
bfe721d1 KH |
374 | @item |
375 | An error message should start with a capital letter but should not end | |
376 | with a period. | |
377 | ||
f37e0163 RS |
378 | @item |
379 | A question asked in the minibuffer with @code{y-or-n-p} or | |
380 | @code{yes-or-no-p} should start with a capital letter and end with | |
381 | @samp{? }. | |
382 | ||
383 | @item | |
384 | When you mention a default value in a minibuffer prompt, | |
385 | put it and the word @samp{default} inside parentheses. | |
386 | It should look like this: | |
387 | ||
388 | @example | |
090be3b6 | 389 | Enter the answer (default 42): |
f37e0163 RS |
390 | @end example |
391 | ||
01e3636e RS |
392 | @item |
393 | In @code{interactive}, if you use a Lisp expression to produce a list | |
394 | of arguments, don't try to provide the ``correct'' default values for | |
395 | region or position arguments. Instead, provide @code{nil} for those | |
396 | arguments if they were not specified, and have the function body | |
397 | compute the default value when the argument is @code{nil}. For | |
398 | instance, write this: | |
399 | ||
400 | @example | |
401 | (defun foo (pos) | |
402 | (interactive | |
403 | (list (if @var{specified} @var{specified-pos}))) | |
404 | (unless pos (setq pos @var{default-pos})) | |
405 | ...) | |
406 | @end example | |
407 | ||
408 | @noindent | |
409 | rather than this: | |
410 | ||
411 | @example | |
412 | (defun foo (pos) | |
413 | (interactive | |
414 | (list (if @var{specified} @var{specified-pos} | |
415 | @var{default-pos}))) | |
416 | ...) | |
417 | @end example | |
418 | ||
419 | @noindent | |
420 | This is so that repetition of the command will recompute | |
421 | these defaults based on the current circumstances. | |
422 | ||
423 | You do not need to take such precautions when you use interactive | |
424 | specs @samp{d}, @samp{m} and @samp{r}, because they make special | |
425 | arrangements to recompute the argument values on repetition of the | |
426 | command. | |
427 | ||
2089b41a RS |
428 | @item |
429 | Many commands that take a long time to execute display a message that | |
01e3636e | 430 | says something like @samp{Operating...} when they start, and change it to |
2089b41a RS |
431 | @samp{Operating...done} when they finish. Please keep the style of |
432 | these messages uniform: @emph{no} space around the ellipsis, and | |
01e3636e | 433 | @emph{no} period after @samp{done}. |
2089b41a | 434 | |
7015aca4 | 435 | @item |
4b6694ef RS |
436 | Try to avoid using recursive edits. Instead, do what the Rmail @kbd{e} |
437 | command does: use a new local keymap that contains one command defined | |
438 | to switch back to the old local keymap. Or do what the | |
439 | @code{edit-options} command does: switch to another buffer and let the | |
440 | user switch back at will. @xref{Recursive Editing}. | |
7015aca4 RS |
441 | @end itemize |
442 | ||
443 | @node Compilation Tips | |
444 | @section Tips for Making Compiled Code Fast | |
445 | @cindex execution speed | |
446 | @cindex speedups | |
447 | ||
448 | Here are ways of improving the execution speed of byte-compiled | |
4b6694ef | 449 | Lisp programs. |
7015aca4 RS |
450 | |
451 | @itemize @bullet | |
452 | @item | |
453 | @cindex profiling | |
454 | @cindex timing programs | |
a9f0a989 | 455 | @cindex @file{elp.el} |
5f7eb05d EZ |
456 | Profile your program with the @file{elp} library. See the file |
457 | @file{elp.el} for instructions. | |
7015aca4 | 458 | |
6b7abae0 RS |
459 | @item |
460 | @cindex @file{benchmark.el} | |
461 | @cindex benchmarking | |
462 | Check the speed of individual Emacs Lisp forms using the | |
463 | @file{benchmark} library. See the functions @code{benchmark-run} and | |
464 | @code{benchmark-run-compiled} in @file{benchmark.el}. | |
465 | ||
7015aca4 RS |
466 | @item |
467 | Use iteration rather than recursion whenever possible. | |
468 | Function calls are slow in Emacs Lisp even when a compiled function | |
469 | is calling another compiled function. | |
470 | ||
471 | @item | |
bfe721d1 KH |
472 | Using the primitive list-searching functions @code{memq}, @code{member}, |
473 | @code{assq}, or @code{assoc} is even faster than explicit iteration. It | |
f9f59935 | 474 | can be worth rearranging a data structure so that one of these primitive |
bfe721d1 | 475 | search functions can be used. |
7015aca4 RS |
476 | |
477 | @item | |
177c0ea7 | 478 | Certain built-in functions are handled specially in byte-compiled code, |
7015aca4 RS |
479 | avoiding the need for an ordinary function call. It is a good idea to |
480 | use these functions rather than alternatives. To see whether a function | |
481 | is handled specially by the compiler, examine its @code{byte-compile} | |
482 | property. If the property is non-@code{nil}, then the function is | |
483 | handled specially. | |
484 | ||
485 | For example, the following input will show you that @code{aref} is | |
a9f0a989 | 486 | compiled specially (@pxref{Array Functions}): |
7015aca4 | 487 | |
4b6694ef | 488 | @example |
7015aca4 RS |
489 | @group |
490 | (get 'aref 'byte-compile) | |
491 | @result{} byte-compile-two-args | |
492 | @end group | |
4b6694ef | 493 | @end example |
7015aca4 RS |
494 | |
495 | @item | |
1911e6e5 | 496 | If calling a small function accounts for a substantial part of your |
7015aca4 RS |
497 | program's running time, make the function inline. This eliminates |
498 | the function call overhead. Since making a function inline reduces | |
499 | the flexibility of changing the program, don't do it unless it gives | |
4b6694ef | 500 | a noticeable speedup in something slow enough that users care about |
7015aca4 RS |
501 | the speed. @xref{Inline Functions}. |
502 | @end itemize | |
503 | ||
5e0fc18a RS |
504 | @node Warning Tips |
505 | @section Tips for Avoiding Compiler Warnings | |
506 | ||
507 | @itemize @bullet | |
508 | @item | |
509 | Try to avoid compiler warnings about undefined free variables, by adding | |
510 | dummy @code{defvar} definitions for these variables, like this: | |
511 | ||
512 | @example | |
513 | (defvar foo) | |
514 | @end example | |
515 | ||
516 | Such a definition has no effect except to tell the compiler | |
517 | not to warn about uses of the variable @code{foo} in this file. | |
518 | ||
519 | @item | |
520 | If you use many functions and variables from a certain file, you can | |
521 | add a @code{require} for that package to avoid compilation warnings | |
522 | for them. For instance, | |
523 | ||
524 | @example | |
525 | (eval-when-compile | |
526 | (require 'foo)) | |
527 | @end example | |
528 | ||
529 | @item | |
530 | If you bind a variable in one function, and use it or set it in | |
531 | another function, the compiler warns about the latter function unless | |
532 | the variable has a definition. But adding a definition would be | |
533 | unclean if the variable has a short name, since Lisp packages should | |
534 | not define short variable names. The right thing to do is to rename | |
535 | this variable to start with the name prefix used for the other | |
536 | functions and variables in your package. | |
537 | ||
538 | @item | |
539 | The last resort for avoiding a warning, when you want to do something | |
540 | that usually is a mistake but it's not a mistake in this one case, | |
541 | is to put a call to @code{with-no-warnings} around it. | |
542 | @end itemize | |
543 | ||
7015aca4 RS |
544 | @node Documentation Tips |
545 | @section Tips for Documentation Strings | |
546 | ||
969fe9b5 RS |
547 | @findex checkdoc-minor-mode |
548 | Here are some tips and conventions for the writing of documentation | |
549 | strings. You can check many of these conventions by running the command | |
550 | @kbd{M-x checkdoc-minor-mode}. | |
7015aca4 RS |
551 | |
552 | @itemize @bullet | |
553 | @item | |
574efc83 | 554 | Every command, function, or variable intended for users to know about |
7015aca4 RS |
555 | should have a documentation string. |
556 | ||
557 | @item | |
e0d32668 RS |
558 | An internal variable or subroutine of a Lisp program might as well have |
559 | a documentation string. In earlier Emacs versions, you could save space | |
560 | by using a comment instead of a documentation string, but that is no | |
2468d0c0 DL |
561 | longer the case---documentation strings now take up very little space in |
562 | a running Emacs. | |
7015aca4 | 563 | |
b090d792 RS |
564 | @item |
565 | Format the documentation string so that it fits in an Emacs window on an | |
566 | 80-column screen. It is a good idea for most lines to be no wider than | |
567 | 60 characters. The first line should not be wider than 67 characters | |
568 | or it will look bad in the output of @code{apropos}. | |
569 | ||
570 | You can fill the text if that looks good. However, rather than blindly | |
571 | filling the entire documentation string, you can often make it much more | |
572 | readable by choosing certain line breaks with care. Use blank lines | |
573 | between topics if the documentation string is long. | |
574 | ||
7015aca4 RS |
575 | @item |
576 | The first line of the documentation string should consist of one or two | |
574efc83 | 577 | complete sentences that stand on their own as a summary. @kbd{M-x |
2468d0c0 DL |
578 | apropos} displays just the first line, and if that line's contents don't |
579 | stand on their own, the result looks bad. In particular, start the | |
580 | first line with a capital letter and end with a period. | |
7015aca4 | 581 | |
aa5dbf7b RS |
582 | For a function, the first line should briefly answer the question, |
583 | ``What does this function do?'' For a variable, the first line should | |
584 | briefly answer the question, ``What does this value mean?'' | |
585 | ||
586 | Don't limit the documentation string to one line; use as many lines as | |
587 | you need to explain the details of how to use the function or | |
588 | variable. Please use complete sentences for the rest of the text too. | |
7015aca4 | 589 | |
7878d6b6 RS |
590 | @item |
591 | The first line should mention all the important arguments of the | |
592 | function, and should mention them in the order that they are written | |
593 | in a function call. If the function has many arguments, then it is | |
594 | not feasible to mention them all in the first line; in that case, the | |
595 | first line should mention the first few arguments, including the most | |
596 | important arguments. | |
597 | ||
4b6694ef | 598 | @item |
8241495d | 599 | For consistency, phrase the verb in the first sentence of a function's |
321a3725 | 600 | documentation string as an imperative---for instance, use ``Return the |
8241495d RS |
601 | cons of A and B.'' in preference to ``Returns the cons of A and B@.'' |
602 | Usually it looks good to do likewise for the rest of the first | |
603 | paragraph. Subsequent paragraphs usually look better if each sentence | |
b090d792 | 604 | is indicative and has a proper subject. |
4b6694ef | 605 | |
7015aca4 RS |
606 | @item |
607 | Write documentation strings in the active voice, not the passive, and in | |
608 | the present tense, not the future. For instance, use ``Return a list | |
609 | containing A and B.'' instead of ``A list containing A and B will be | |
610 | returned.'' | |
611 | ||
612 | @item | |
613 | Avoid using the word ``cause'' (or its equivalents) unnecessarily. | |
614 | Instead of, ``Cause Emacs to display text in boldface,'' write just | |
615 | ``Display text in boldface.'' | |
616 | ||
2468d0c0 DL |
617 | @item |
618 | When a command is meaningful only in a certain mode or situation, | |
619 | do mention that in the documentation string. For example, | |
620 | the documentation of @code{dired-find-file} is: | |
621 | ||
622 | @example | |
623 | In Dired, visit the file or directory named on this line. | |
624 | @end example | |
625 | ||
7015aca4 RS |
626 | @item |
627 | Do not start or end a documentation string with whitespace. | |
177c0ea7 | 628 | |
7015aca4 RS |
629 | @item |
630 | @strong{Do not} indent subsequent lines of a documentation string so | |
631 | that the text is lined up in the source code with the text of the first | |
632 | line. This looks nice in the source code, but looks bizarre when users | |
633 | view the documentation. Remember that the indentation before the | |
634 | starting double-quote is not part of the string! | |
635 | ||
75d97f47 RS |
636 | @item |
637 | When the user tries to use a disabled command, Emacs displays just the | |
638 | first paragraph of its documentation string---everything through the | |
639 | first blank line. If you wish, you can choose which information to | |
640 | include before the first blank line so as to make this display useful. | |
641 | ||
7015aca4 | 642 | @item |
eef4e174 | 643 | When you define a variable that users ought to set interactively, you |
d8ea07f6 | 644 | normally should use @code{defcustom}. However, if for some reason you |
eef4e174 LT |
645 | use @code{defvar} instead, start the doc string with a @samp{*}. |
646 | @xref{Defining Variables}. | |
7015aca4 RS |
647 | |
648 | @item | |
649 | The documentation string for a variable that is a yes-or-no flag should | |
4b6694ef RS |
650 | start with words such as ``Non-nil means@dots{}'', to make it clear that |
651 | all non-@code{nil} values are equivalent and indicate explicitly what | |
652 | @code{nil} and non-@code{nil} mean. | |
7015aca4 | 653 | |
5c5b7d3e RS |
654 | @item |
655 | The documentation string for a function that is a yes-or-no predicate | |
656 | should start with words such as ``Return t if @dots{}'', to indicate | |
657 | explicitly what constitutes ``truth''. The word ``return'' avoids | |
658 | starting the sentence with lower-case ``t'', which is somewhat | |
659 | distracting. | |
660 | ||
7015aca4 RS |
661 | @item |
662 | When a function's documentation string mentions the value of an argument | |
663 | of the function, use the argument name in capital letters as if it were | |
664 | a name for that value. Thus, the documentation string of the function | |
2468d0c0 DL |
665 | @code{eval} refers to its second argument as @samp{FORM}, because the |
666 | actual argument name is @code{form}: | |
667 | ||
668 | @example | |
669 | Evaluate FORM and return its value. | |
670 | @end example | |
7015aca4 | 671 | |
2468d0c0 DL |
672 | Also write metasyntactic variables in capital letters, such as when you |
673 | show the decomposition of a list or vector into subunits, some of which | |
674 | may vary. @samp{KEY} and @samp{VALUE} in the following example | |
8241495d RS |
675 | illustrate this practice: |
676 | ||
677 | @example | |
678 | The argument TABLE should be an alist whose elements | |
679 | have the form (KEY . VALUE). Here, KEY is ... | |
680 | @end example | |
7015aca4 | 681 | |
5c5b7d3e RS |
682 | @item |
683 | Never change the case of a Lisp symbol when you mention it in a doc | |
684 | string. If the symbol's name is @code{foo}, write ``foo'', not | |
685 | ``Foo'' (which is a different symbol). | |
686 | ||
687 | This might appear to contradict the policy of writing function | |
688 | argument values, but there is no real contradiction; the argument | |
689 | @emph{value} is not the same thing as the @emph{symbol} which the | |
690 | function uses to hold the value. | |
691 | ||
692 | If this puts a lower-case letter at the beginning of a sentence | |
693 | and that annoys you, rewrite the sentence so that the symbol | |
694 | is not at the start of it. | |
695 | ||
2468d0c0 DL |
696 | @item |
697 | If a line in a documentation string begins with an open-parenthesis, | |
698 | write a backslash before the open-parenthesis, like this: | |
699 | ||
700 | @example | |
701 | The argument FOO can be either a number | |
702 | \(a buffer position) or a string (a file name). | |
703 | @end example | |
704 | ||
705 | This prevents the open-parenthesis from being treated as the start of a | |
706 | defun (@pxref{Defuns,, Defuns, emacs, The GNU Emacs Manual}). | |
707 | ||
70057f39 | 708 | @anchor{Docstring hyperlinks} |
7015aca4 RS |
709 | @item |
710 | @iftex | |
711 | When a documentation string refers to a Lisp symbol, write it as it | |
712 | would be printed (which usually means in lower case), with single-quotes | |
713 | around it. For example: @samp{`lambda'}. There are two exceptions: | |
714 | write @code{t} and @code{nil} without single-quotes. | |
715 | @end iftex | |
37680279 | 716 | @ifnottex |
7015aca4 RS |
717 | When a documentation string refers to a Lisp symbol, write it as it |
718 | would be printed (which usually means in lower case), with single-quotes | |
719 | around it. For example: @samp{lambda}. There are two exceptions: write | |
969fe9b5 RS |
720 | t and nil without single-quotes. (In this manual, we use a different |
721 | convention, with single-quotes for all symbols.) | |
37680279 | 722 | @end ifnottex |
7015aca4 | 723 | |
1911e6e5 RS |
724 | Help mode automatically creates a hyperlink when a documentation string |
725 | uses a symbol name inside single quotes, if the symbol has either a | |
a9f0a989 RS |
726 | function or a variable definition. You do not need to do anything |
727 | special to make use of this feature. However, when a symbol has both a | |
728 | function definition and a variable definition, and you want to refer to | |
729 | just one of them, you can specify which one by writing one of the words | |
730 | @samp{variable}, @samp{option}, @samp{function}, or @samp{command}, | |
731 | immediately before the symbol name. (Case makes no difference in | |
732 | recognizing these indicator words.) For example, if you write | |
733 | ||
734 | @example | |
735 | This function sets the variable `buffer-file-name'. | |
736 | @end example | |
737 | ||
738 | @noindent | |
739 | then the hyperlink will refer only to the variable documentation of | |
740 | @code{buffer-file-name}, and not to its function documentation. | |
741 | ||
742 | If a symbol has a function definition and/or a variable definition, but | |
743 | those are irrelevant to the use of the symbol that you are documenting, | |
744 | you can write the word @samp{symbol} before the symbol name to prevent | |
745 | making any hyperlink. For example, | |
969fe9b5 RS |
746 | |
747 | @example | |
a9f0a989 RS |
748 | If the argument KIND-OF-RESULT is the symbol `list', |
749 | this function returns a list of all the objects | |
750 | that satisfy the criterion. | |
969fe9b5 RS |
751 | @end example |
752 | ||
a9f0a989 RS |
753 | @noindent |
754 | does not make a hyperlink to the documentation, irrelevant here, of the | |
755 | function @code{list}. | |
756 | ||
e72850d5 LT |
757 | Normally, no hyperlink is made for a variable without variable |
758 | documentation. You can force a hyperlink for such variables by | |
759 | preceding them with one of the words @samp{variable} or | |
760 | @samp{option}. | |
761 | ||
762 | Hyperlinks for faces are only made if the face name is preceded or | |
763 | followed by the word @samp{face}. In that case, only the face | |
764 | documentation will be shown, even if the symbol is also defined as a | |
765 | variable or as a function. | |
766 | ||
8241495d | 767 | To make a hyperlink to Info documentation, write the name of the Info |
727c9159 LT |
768 | node (or anchor) in single quotes, preceded by @samp{info node}, |
769 | @samp{Info node}, @samp{info anchor} or @samp{Info anchor}. The Info | |
770 | file name defaults to @samp{emacs}. For example, | |
8241495d RS |
771 | |
772 | @smallexample | |
773 | See Info node `Font Lock' and Info node `(elisp)Font Lock Basics'. | |
774 | @end smallexample | |
775 | ||
7000848e BW |
776 | Finally, to create a hyperlink to URLs, write the URL in single |
777 | quotes, preceded by @samp{URL}. For example, | |
778 | ||
779 | @smallexample | |
780 | The home page for the GNU project has more information (see URL | |
781 | `http://www.gnu.org/'). | |
782 | @end smallexample | |
783 | ||
7015aca4 RS |
784 | @item |
785 | Don't write key sequences directly in documentation strings. Instead, | |
786 | use the @samp{\\[@dots{}]} construct to stand for them. For example, | |
9e2b495b RS |
787 | instead of writing @samp{C-f}, write the construct |
788 | @samp{\\[forward-char]}. When Emacs displays the documentation string, | |
789 | it substitutes whatever key is currently bound to @code{forward-char}. | |
790 | (This is normally @samp{C-f}, but it may be some other character if the | |
791 | user has moved key bindings.) @xref{Keys in Documentation}. | |
7015aca4 RS |
792 | |
793 | @item | |
794 | In documentation strings for a major mode, you will want to refer to the | |
795 | key bindings of that mode's local map, rather than global ones. | |
796 | Therefore, use the construct @samp{\\<@dots{}>} once in the | |
797 | documentation string to specify which key map to use. Do this before | |
798 | the first use of @samp{\\[@dots{}]}. The text inside the | |
799 | @samp{\\<@dots{}>} should be the name of the variable containing the | |
800 | local keymap for the major mode. | |
801 | ||
802 | It is not practical to use @samp{\\[@dots{}]} very many times, because | |
803 | display of the documentation string will become slow. So use this to | |
804 | describe the most important commands in your major mode, and then use | |
805 | @samp{\\@{@dots{}@}} to display the rest of the mode's keymap. | |
7015aca4 RS |
806 | @end itemize |
807 | ||
808 | @node Comment Tips | |
809 | @section Tips on Writing Comments | |
810 | ||
811 | We recommend these conventions for where to put comments and how to | |
812 | indent them: | |
813 | ||
814 | @table @samp | |
815 | @item ; | |
816 | Comments that start with a single semicolon, @samp{;}, should all be | |
817 | aligned to the same column on the right of the source code. Such | |
818 | comments usually explain how the code on the same line does its job. In | |
819 | Lisp mode and related modes, the @kbd{M-;} (@code{indent-for-comment}) | |
820 | command automatically inserts such a @samp{;} in the right place, or | |
4b6694ef | 821 | aligns such a comment if it is already present. |
7015aca4 | 822 | |
574efc83 | 823 | This and following examples are taken from the Emacs sources. |
7015aca4 RS |
824 | |
825 | @smallexample | |
826 | @group | |
827 | (setq base-version-list ; there was a base | |
828 | (assoc (substring fn 0 start-vn) ; version to which | |
829 | file-version-assoc-list)) ; this looks like | |
830 | ; a subversion | |
831 | @end group | |
832 | @end smallexample | |
833 | ||
834 | @item ;; | |
835 | Comments that start with two semicolons, @samp{;;}, should be aligned to | |
4b6694ef | 836 | the same level of indentation as the code. Such comments usually |
7015aca4 RS |
837 | describe the purpose of the following lines or the state of the program |
838 | at that point. For example: | |
839 | ||
840 | @smallexample | |
841 | @group | |
842 | (prog1 (setq auto-fill-function | |
843 | @dots{} | |
844 | @dots{} | |
4b6694ef | 845 | ;; update mode line |
7015aca4 RS |
846 | (force-mode-line-update))) |
847 | @end group | |
848 | @end smallexample | |
849 | ||
2468d0c0 | 850 | We also normally use two semicolons for comments outside functions. |
7015aca4 RS |
851 | |
852 | @smallexample | |
853 | @group | |
2468d0c0 DL |
854 | ;; This Lisp code is run in Emacs |
855 | ;; when it is to operate as a server | |
856 | ;; for other processes. | |
7015aca4 RS |
857 | @end group |
858 | @end smallexample | |
859 | ||
2468d0c0 DL |
860 | Every function that has no documentation string (presumably one that is |
861 | used only internally within the package it belongs to), should instead | |
862 | have a two-semicolon comment right before the function, explaining what | |
863 | the function does and how to call it properly. Explain precisely what | |
864 | each argument means and how the function interprets its possible values. | |
865 | ||
866 | @item ;;; | |
867 | Comments that start with three semicolons, @samp{;;;}, should start at | |
868 | the left margin. These are used, occasionally, for comments within | |
869 | functions that should start at the margin. We also use them sometimes | |
870 | for comments that are between functions---whether to use two or three | |
dd4a1d28 LT |
871 | semicolons depends on whether the comment should be considered a |
872 | ``heading'' by Outline minor mode. By default, comments starting with | |
873 | at least three semicolons (followed by a single space and a | |
874 | non-whitespace character) are considered headings, comments starting | |
875 | with two or less are not. | |
2468d0c0 | 876 | |
574efc83 | 877 | Another use for triple-semicolon comments is for commenting out lines |
2468d0c0 | 878 | within a function. We use three semicolons for this precisely so that |
dd4a1d28 LT |
879 | they remain at the left margin. By default, Outline minor mode does |
880 | not consider a comment to be a heading (even if it starts with at | |
881 | least three semicolons) if the semicolons are followed by at least two | |
882 | spaces. Thus, if you add an introductory comment to the commented out | |
883 | code, make sure to indent it by at least two spaces after the three | |
884 | semicolons. | |
4b6694ef RS |
885 | |
886 | @smallexample | |
887 | (defun foo (a) | |
dd4a1d28 | 888 | ;;; This is no longer necessary. |
4b6694ef RS |
889 | ;;; (force-mode-line-update) |
890 | (message "Finished with %s" a)) | |
891 | @end smallexample | |
892 | ||
dd4a1d28 LT |
893 | When commenting out entire functions, use two semicolons. |
894 | ||
7015aca4 RS |
895 | @item ;;;; |
896 | Comments that start with four semicolons, @samp{;;;;}, should be aligned | |
897 | to the left margin and are used for headings of major sections of a | |
898 | program. For example: | |
899 | ||
900 | @smallexample | |
901 | ;;;; The kill ring | |
902 | @end smallexample | |
903 | @end table | |
904 | ||
905 | @noindent | |
906 | The indentation commands of the Lisp modes in Emacs, such as @kbd{M-;} | |
969fe9b5 | 907 | (@code{indent-for-comment}) and @key{TAB} (@code{lisp-indent-line}), |
7015aca4 | 908 | automatically indent comments according to these conventions, |
574efc83 | 909 | depending on the number of semicolons. @xref{Comments,, |
7015aca4 RS |
910 | Manipulating Comments, emacs, The GNU Emacs Manual}. |
911 | ||
7015aca4 RS |
912 | @node Library Headers |
913 | @section Conventional Headers for Emacs Libraries | |
914 | @cindex header comments | |
915 | @cindex library header comments | |
916 | ||
f9f59935 | 917 | Emacs has conventions for using special comments in Lisp libraries |
7015aca4 | 918 | to divide them into sections and give information such as who wrote |
8241495d RS |
919 | them. This section explains these conventions. |
920 | ||
921 | We'll start with an example, a package that is included in the Emacs | |
922 | distribution. | |
923 | ||
924 | Parts of this example reflect its status as part of Emacs; for | |
925 | example, the copyright notice lists the Free Software Foundation as the | |
926 | copyright holder, and the copying permission says the file is part of | |
927 | Emacs. When you write a package and post it, the copyright holder would | |
928 | be you (unless your employer claims to own it instead), and you should | |
929 | get the suggested copying permission from the end of the GNU General | |
930 | Public License itself. Don't say your file is part of Emacs | |
931 | if we haven't installed it in Emacs yet! | |
932 | ||
933 | With that warning out of the way, on to the example: | |
7015aca4 RS |
934 | |
935 | @smallexample | |
936 | @group | |
937 | ;;; lisp-mnt.el --- minor mode for Emacs Lisp maintainers | |
938 | ||
939 | ;; Copyright (C) 1992 Free Software Foundation, Inc. | |
940 | @end group | |
941 | ||
942 | ;; Author: Eric S. Raymond <esr@@snark.thyrsus.com> | |
943 | ;; Maintainer: Eric S. Raymond <esr@@snark.thyrsus.com> | |
944 | ;; Created: 14 Jul 1992 | |
945 | ;; Version: 1.2 | |
946 | @group | |
947 | ;; Keywords: docs | |
948 | ||
949 | ;; This file is part of GNU Emacs. | |
969fe9b5 | 950 | @dots{} |
086add15 LK |
951 | ;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, |
952 | ;; Boston, MA 02110-1301, USA. | |
7015aca4 RS |
953 | @end group |
954 | @end smallexample | |
955 | ||
956 | The very first line should have this format: | |
957 | ||
958 | @example | |
959 | ;;; @var{filename} --- @var{description} | |
960 | @end example | |
961 | ||
962 | @noindent | |
e4317c8c RS |
963 | The description should be complete in one line. If the file |
964 | needs a @samp{-*-} specification, put it after @var{description}. | |
7015aca4 RS |
965 | |
966 | After the copyright notice come several @dfn{header comment} lines, | |
4b6694ef | 967 | each beginning with @samp{;; @var{header-name}:}. Here is a table of |
7015aca4 RS |
968 | the conventional possibilities for @var{header-name}: |
969 | ||
970 | @table @samp | |
971 | @item Author | |
972 | This line states the name and net address of at least the principal | |
973 | author of the library. | |
974 | ||
975 | If there are multiple authors, you can list them on continuation lines | |
4b6694ef | 976 | led by @code{;;} and a tab character, like this: |
7015aca4 RS |
977 | |
978 | @smallexample | |
979 | @group | |
980 | ;; Author: Ashwin Ram <Ram-Ashwin@@cs.yale.edu> | |
4b6694ef RS |
981 | ;; Dave Sill <de5@@ornl.gov> |
982 | ;; Dave Brennan <brennan@@hal.com> | |
983 | ;; Eric Raymond <esr@@snark.thyrsus.com> | |
7015aca4 RS |
984 | @end group |
985 | @end smallexample | |
986 | ||
987 | @item Maintainer | |
988 | This line should contain a single name/address as in the Author line, or | |
4b6694ef RS |
989 | an address only, or the string @samp{FSF}. If there is no maintainer |
990 | line, the person(s) in the Author field are presumed to be the | |
991 | maintainers. The example above is mildly bogus because the maintainer | |
992 | line is redundant. | |
7015aca4 RS |
993 | |
994 | The idea behind the @samp{Author} and @samp{Maintainer} lines is to make | |
995 | possible a Lisp function to ``send mail to the maintainer'' without | |
996 | having to mine the name out by hand. | |
997 | ||
998 | Be sure to surround the network address with @samp{<@dots{}>} if | |
999 | you include the person's full name as well as the network address. | |
1000 | ||
1001 | @item Created | |
1002 | This optional line gives the original creation date of the | |
1003 | file. For historical interest only. | |
1004 | ||
1005 | @item Version | |
1006 | If you wish to record version numbers for the individual Lisp program, put | |
1007 | them in this line. | |
1008 | ||
1009 | @item Adapted-By | |
1010 | In this header line, place the name of the person who adapted the | |
1011 | library for installation (to make it fit the style conventions, for | |
1012 | example). | |
1013 | ||
1014 | @item Keywords | |
1015 | This line lists keywords for the @code{finder-by-keyword} help command. | |
a9f0a989 RS |
1016 | Please use that command to see a list of the meaningful keywords. |
1017 | ||
7015aca4 | 1018 | This field is important; it's how people will find your package when |
2c62739d RS |
1019 | they're looking for things by topic area. To separate the keywords, you |
1020 | can use spaces, commas, or both. | |
7015aca4 RS |
1021 | @end table |
1022 | ||
1023 | Just about every Lisp library ought to have the @samp{Author} and | |
1024 | @samp{Keywords} header comment lines. Use the others if they are | |
1025 | appropriate. You can also put in header lines with other header | |
1026 | names---they have no standard meanings, so they can't do any harm. | |
1027 | ||
1028 | We use additional stylized comments to subdivide the contents of the | |
2468d0c0 DL |
1029 | library file. These should be separated by blank lines from anything |
1030 | else. Here is a table of them: | |
7015aca4 RS |
1031 | |
1032 | @table @samp | |
1033 | @item ;;; Commentary: | |
1034 | This begins introductory comments that explain how the library works. | |
a9f0a989 RS |
1035 | It should come right after the copying permissions, terminated by a |
1036 | @samp{Change Log}, @samp{History} or @samp{Code} comment line. This | |
1037 | text is used by the Finder package, so it should make sense in that | |
1038 | context. | |
1039 | ||
fd423b79 | 1040 | @item ;;; Documentation: |
3ff91798 RS |
1041 | This was used in some files in place of @samp{;;; Commentary:}, |
1042 | but it is deprecated. | |
7015aca4 | 1043 | |
a9f0a989 | 1044 | @item ;;; Change Log: |
7015aca4 | 1045 | This begins change log information stored in the library file (if you |
2468d0c0 DL |
1046 | store the change history there). For Lisp files distributed with Emacs, |
1047 | the change history is kept in the file @file{ChangeLog} and not in the | |
1048 | source file at all; these files generally do not have a @samp{;;; Change | |
1049 | Log:} line. @samp{History} is an alternative to @samp{Change Log}. | |
7015aca4 RS |
1050 | |
1051 | @item ;;; Code: | |
1052 | This begins the actual code of the program. | |
1053 | ||
1054 | @item ;;; @var{filename} ends here | |
1055 | This is the @dfn{footer line}; it appears at the very end of the file. | |
1056 | Its purpose is to enable people to detect truncated versions of the file | |
1057 | from the lack of a footer line. | |
1058 | @end table | |
ab5796a9 MB |
1059 | |
1060 | @ignore | |
1061 | arch-tag: 9ea911c2-6b1d-47dd-88b7-0a94e8b27c2e | |
1062 | @end ignore |