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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 | |
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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 | |
038783e6 | 38 | @cindex coding conventions in Emacs Lisp |
2323275b RS |
39 | Here are conventions that you should follow when writing Emacs Lisp |
40 | code intended for widespread use: | |
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41 | |
42 | @itemize @bullet | |
424402ec RS |
43 | @item |
44 | Simply loading the package should not change Emacs's editing behavior. | |
45 | Include a command or commands to enable and disable the feature, | |
46 | or to invoke it. | |
47 | ||
48 | This convention is mandatory for any file that includes custom | |
49 | definitions. If fixing such a file to follow this convention requires | |
50 | an incompatible change, go ahead and make the incompatible change; | |
51 | don't postpone it. | |
52 | ||
7015aca4 | 53 | @item |
92204c92 RS |
54 | Since all global variables share the same name space, and all |
55 | functions share another name space, you should choose a short word to | |
038783e6 | 56 | distinguish your program from other Lisp programs@footnote{The |
92204c92 | 57 | benefits of a Common Lisp-style package system are considered not to |
038783e6 | 58 | outweigh the costs.}. Then take care to begin the names of all global |
92204c92 | 59 | variables, constants, and functions in your program with the chosen |
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60 | prefix. This helps avoid name conflicts. |
61 | ||
62 | Occasionally, for a command name intended for users to use, it is more | |
63 | convenient if some words come before the package's name prefix. And | |
64 | constructs that define functions, variables, etc., work better if they | |
65 | start with @samp{defun} or @samp{defvar}, so put the name prefix later | |
66 | on in the name. | |
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67 | |
68 | This recommendation applies even to names for traditional Lisp | |
378d0f8e | 69 | primitives that are not primitives in Emacs Lisp---such as |
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70 | @code{copy-list}. Believe it or not, there is more than one plausible |
71 | way to define @code{copy-list}. Play it safe; append your name prefix | |
72 | to produce a name like @code{foo-copy-list} or @code{mylib-copy-list} | |
73 | instead. | |
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74 | |
75 | If you write a function that you think ought to be added to Emacs under | |
76 | a certain name, such as @code{twiddle-files}, don't call it by that name | |
77 | in your program. Call it @code{mylib-twiddle-files} in your program, | |
a9f0a989 | 78 | and send mail to @samp{bug-gnu-emacs@@gnu.org} suggesting we add |
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79 | it to Emacs. If and when we do, we can change the name easily enough. |
80 | ||
5e0fc18a | 81 | If one prefix is insufficient, your package can use two or three |
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82 | alternative common prefixes, so long as they make sense. |
83 | ||
84 | Separate the prefix from the rest of the symbol name with a hyphen, | |
85 | @samp{-}. This will be consistent with Emacs itself and with most Emacs | |
86 | Lisp programs. | |
87 | ||
88 | @item | |
5e0fc18a | 89 | Put a call to @code{provide} at the end of each separate Lisp file. |
7015aca4 | 90 | |
bfe721d1 | 91 | @item |
5e0fc18a | 92 | If a file requires certain other Lisp programs to be loaded |
bfe721d1 KH |
93 | beforehand, then the comments at the beginning of the file should say |
94 | so. Also, use @code{require} to make sure they are loaded. | |
95 | ||
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96 | @item |
97 | If one file @var{foo} uses a macro defined in another file @var{bar}, | |
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98 | @var{foo} should contain this expression before the first use of the |
99 | macro: | |
100 | ||
101 | @example | |
102 | (eval-when-compile (require '@var{bar})) | |
103 | @end example | |
104 | ||
105 | @noindent | |
969fe9b5 RS |
106 | (And the library @var{bar} should contain @code{(provide '@var{bar})}, |
107 | to make the @code{require} work.) This will cause @var{bar} to be | |
108 | loaded when you byte-compile @var{foo}. Otherwise, you risk compiling | |
109 | @var{foo} without the necessary macro loaded, and that would produce | |
110 | compiled code that won't work right. @xref{Compiling Macros}. | |
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111 | |
112 | Using @code{eval-when-compile} avoids loading @var{bar} when | |
113 | the compiled version of @var{foo} is @emph{used}. | |
7015aca4 | 114 | |
becd5943 KH |
115 | @item |
116 | Please don't require the @code{cl} package of Common Lisp extensions at | |
117 | run time. Use of this package is optional, and it is not part of the | |
118 | standard Emacs namespace. If your package loads @code{cl} at run time, | |
119 | that could cause name clashes for users who don't use that package. | |
120 | ||
c876e7b7 | 121 | However, there is no problem with using the @code{cl} package at |
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122 | compile time, with @code{(eval-when-compile (require 'cl))}. That's |
123 | sufficient for using the macros in the @code{cl} package, because the | |
124 | compiler expands them before generating the byte-code. | |
becd5943 | 125 | |
7015aca4 | 126 | @item |
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127 | When defining a major mode, please follow the major mode |
128 | conventions. @xref{Major Mode Conventions}. | |
129 | ||
130 | @item | |
131 | When defining a minor mode, please follow the minor mode | |
132 | conventions. @xref{Minor Mode Conventions}. | |
7015aca4 | 133 | |
6cbf476c RS |
134 | @item |
135 | If the purpose of a function is to tell you whether a certain condition | |
136 | is true or false, give the function a name that ends in @samp{p}. If | |
137 | the name is one word, add just @samp{p}; if the name is multiple words, | |
138 | add @samp{-p}. Examples are @code{framep} and @code{frame-live-p}. | |
139 | ||
140 | @item | |
141 | If a user option variable records a true-or-false condition, give it a | |
142 | name that ends in @samp{-flag}. | |
143 | ||
49247521 LK |
144 | @item |
145 | If the purpose of a variable is to store a single function, give it a | |
146 | name that ends in @samp{-function}. If the purpose of a variable is | |
147 | to store a list of functions (i.e., the variable is a hook), please | |
148 | follow the naming conventions for hooks. @xref{Hooks}. | |
149 | ||
5e0fc18a RS |
150 | @item |
151 | @cindex unloading packages | |
152 | If loading the file adds functions to hooks, define a function | |
153 | @code{@var{feature}-unload-hook}, where @var{feature} is the name of | |
154 | the feature the package provides, and make it undo any such changes. | |
155 | Using @code{unload-feature} to unload the file will run this function. | |
156 | @xref{Unloading}. | |
157 | ||
158 | @item | |
159 | It is a bad idea to define aliases for the Emacs primitives. Normally | |
160 | you should use the standard names instead. The case where an alias | |
161 | may be useful is where it facilitates backwards compatibility or | |
162 | portability. | |
163 | ||
164 | @item | |
165 | If a package needs to define an alias or a new function for | |
166 | compatibility with some other version of Emacs, name it with the package | |
167 | prefix, not with the raw name with which it occurs in the other version. | |
168 | Here is an example from Gnus, which provides many examples of such | |
169 | compatibility issues. | |
170 | ||
171 | @example | |
172 | (defalias 'gnus-point-at-bol | |
173 | (if (fboundp 'point-at-bol) | |
174 | 'point-at-bol | |
175 | 'line-beginning-position)) | |
176 | @end example | |
177 | ||
178 | @item | |
688e9e8c | 179 | Redefining (or advising) an Emacs primitive is a bad idea. It may do |
5e0fc18a | 180 | the right thing for a particular program, but there is no telling what |
688e9e8c | 181 | other programs might break as a result. In any case, it is a problem |
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182 | for debugging, because the advised function doesn't do what its source |
183 | code says it does. If the programmer investigating the problem is | |
184 | unaware that there is advice on the function, the experience can be | |
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185 | very frustrating. |
186 | ||
187 | We hope to remove all the places in Emacs that advise primitives. | |
188 | In the mean time, please don't add any more. | |
189 | ||
190 | @item | |
191 | It is likewise a bad idea for one Lisp package to advise a function | |
192 | in another Lisp package. | |
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193 | |
194 | @item | |
195 | Likewise, avoid using @code{eval-after-load} (@pxref{Hooks for | |
196 | Loading}) in libraries and packages. This feature is meant for | |
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197 | personal customizations; using it in a Lisp program is unclean, |
198 | because it modifies the behavior of another Lisp file in a way that's | |
199 | not visible in that file. This is an obstacle for debugging, much | |
200 | like advising a function in the other package. | |
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201 | |
202 | @item | |
203 | If a file does replace any of the functions or library programs of | |
204 | standard Emacs, prominent comments at the beginning of the file should | |
205 | say which functions are replaced, and how the behavior of the | |
206 | replacements differs from that of the originals. | |
207 | ||
208 | @item | |
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209 | Constructs that define a function or variable should be macros, |
210 | not functions, and their names should start with @samp{def}. | |
211 | ||
212 | @item | |
213 | Macros that define a functions or variables should take the name to be | |
214 | defined as the first argument. That will help various tools find the | |
215 | definition automatically. Avoid constructing the names in the macro | |
216 | itself, since that would confuse these tools. | |
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217 | |
218 | @item | |
219 | Please keep the names of your Emacs Lisp source files to 13 characters | |
220 | or less. This way, if the files are compiled, the compiled files' names | |
221 | will be 14 characters or less, which is short enough to fit on all kinds | |
222 | of Unix systems. | |
223 | ||
224 | @item | |
225 | In some other systems there is a convention of choosing variable names | |
226 | that begin and end with @samp{*}. We don't use that convention in Emacs | |
227 | Lisp, so please don't use it in your programs. (Emacs uses such names | |
228 | only for special-purpose buffers.) The users will find Emacs more | |
229 | coherent if all libraries use the same conventions. | |
230 | ||
4c02cf86 RS |
231 | @item |
232 | If your program contains non-ASCII characters in string or character | |
233 | constants, you should make sure Emacs always decodes these characters | |
234 | the same way, regardless of the user's settings. There are two ways | |
235 | to do that: | |
236 | ||
237 | @itemize - | |
238 | @item | |
239 | Use coding system @code{emacs-mule}, and specify that for | |
240 | @code{coding} in the @samp{-*-} line or the local variables list. | |
241 | ||
242 | @example | |
243 | ;; XXX.el -*- coding: emacs-mule; -*- | |
244 | @end example | |
245 | ||
246 | @item | |
247 | Use one of the coding systems based on ISO 2022 (such as | |
248 | iso-8859-@var{n} and iso-2022-7bit), and specify it with @samp{!} at | |
249 | the end for @code{coding}. (The @samp{!} turns off any possible | |
250 | character translation.) | |
251 | ||
252 | @example | |
253 | ;; XXX.el -*- coding: iso-latin-2!; -*- | |
254 | @end example | |
503b5e1c | 255 | @end itemize |
4c02cf86 | 256 | |
5e0fc18a RS |
257 | @item |
258 | Indent each function with @kbd{C-M-q} (@code{indent-sexp}) using the | |
259 | default indentation parameters. | |
260 | ||
261 | @item | |
262 | Don't make a habit of putting close-parentheses on lines by themselves; | |
263 | Lisp programmers find this disconcerting. Once in a while, when there | |
264 | is a sequence of many consecutive close-parentheses, it may make sense | |
265 | to split the sequence in one or two significant places. | |
266 | ||
267 | @item | |
268 | Please put a copyright notice and copying permission notice on the | |
269 | file if you distribute copies. Use a notice like this one: | |
270 | ||
271 | @smallexample | |
272 | ;; Copyright (C) @var{year} @var{name} | |
273 | ||
274 | ;; This program is free software; you can redistribute it and/or | |
275 | ;; modify it under the terms of the GNU General Public License as | |
276 | ;; published by the Free Software Foundation; either version 2 of | |
277 | ;; the License, or (at your option) any later version. | |
278 | ||
279 | ;; This program is distributed in the hope that it will be | |
280 | ;; useful, but WITHOUT ANY WARRANTY; without even the implied | |
281 | ;; warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR | |
282 | ;; PURPOSE. See the GNU General Public License for more details. | |
283 | ||
284 | ;; You should have received a copy of the GNU General Public | |
285 | ;; License along with this program; if not, write to the Free | |
42b50684 KB |
286 | ;; Software Foundation, Inc., 51 Franklin Street, Fifth Floor, |
287 | ;; Boston, MA 02110-1301 USA | |
5e0fc18a RS |
288 | @end smallexample |
289 | ||
290 | If you have signed papers to assign the copyright to the Foundation, | |
291 | then use @samp{Free Software Foundation, Inc.} as @var{name}. | |
292 | Otherwise, use your name. See also @xref{Library Headers}. | |
293 | @end itemize | |
294 | ||
295 | @node Key Binding Conventions | |
296 | @section Key Binding Conventions | |
297 | ||
298 | @itemize @bullet | |
299 | @item | |
300 | @cindex mouse-2 | |
301 | @cindex references, following | |
302 | Special major modes used for read-only text should usually redefine | |
303 | @kbd{mouse-2} and @key{RET} to trace some sort of reference in the text. | |
304 | Modes such as Dired, Info, Compilation, and Occur redefine it in this | |
305 | way. | |
306 | ||
307 | In addition, they should mark the text as a kind of ``link'' so that | |
308 | @kbd{mouse-1} will follow it also. @xref{Links and Mouse-1}. | |
309 | ||
7015aca4 | 310 | @item |
a9f0a989 RS |
311 | @cindex reserved keys |
312 | @cindex keys, reserved | |
378d0f8e RS |
313 | Please do not define @kbd{C-c @var{letter}} as a key in Lisp programs. |
314 | Sequences consisting of @kbd{C-c} and a letter (either upper or lower | |
315 | case) are reserved for users; they are the @strong{only} sequences | |
316 | reserved for users, so do not block them. | |
7015aca4 | 317 | |
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318 | Changing all the Emacs major modes to respect this convention was a |
319 | lot of work; abandoning this convention would make that work go to | |
320 | waste, and inconvenience users. Please comply with it. | |
7015aca4 | 321 | |
378d0f8e RS |
322 | @item |
323 | Function keys @key{F5} through @key{F9} without modifier keys are | |
324 | also reserved for users to define. | |
325 | ||
326 | @item | |
327 | Applications should not bind mouse events based on button 1 with the | |
328 | shift key held down. These events include @kbd{S-mouse-1}, | |
329 | @kbd{M-S-mouse-1}, @kbd{C-S-mouse-1}, and so on. They are reserved for | |
330 | users. | |
331 | ||
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332 | @item |
333 | Sequences consisting of @kbd{C-c} followed by a control character or a | |
334 | digit are reserved for major modes. | |
00d96ada RS |
335 | |
336 | @item | |
337 | Sequences consisting of @kbd{C-c} followed by @kbd{@{}, @kbd{@}}, | |
338 | @kbd{<}, @kbd{>}, @kbd{:} or @kbd{;} are also reserved for major modes. | |
339 | ||
340 | @item | |
341 | Sequences consisting of @kbd{C-c} followed by any other punctuation | |
342 | character are allocated for minor modes. Using them in a major mode is | |
343 | not absolutely prohibited, but if you do that, the major mode binding | |
344 | may be shadowed from time to time by minor modes. | |
7015aca4 RS |
345 | |
346 | @item | |
f9f59935 | 347 | Do not bind @kbd{C-h} following any prefix character (including |
7015aca4 RS |
348 | @kbd{C-c}). If you don't bind @kbd{C-h}, it is automatically available |
349 | as a help character for listing the subcommands of the prefix character. | |
350 | ||
351 | @item | |
f9f59935 | 352 | Do not bind a key sequence ending in @key{ESC} except following |
969fe9b5 | 353 | another @key{ESC}. (That is, it is OK to bind a sequence ending in |
7015aca4 RS |
354 | @kbd{@key{ESC} @key{ESC}}.) |
355 | ||
356 | The reason for this rule is that a non-prefix binding for @key{ESC} in | |
357 | any context prevents recognition of escape sequences as function keys in | |
358 | that context. | |
359 | ||
52c90d84 RS |
360 | @item |
361 | Anything which acts like a temporary mode or state which the user can | |
b6ae404e | 362 | enter and leave should define @kbd{@key{ESC} @key{ESC}} or |
52c90d84 RS |
363 | @kbd{@key{ESC} @key{ESC} @key{ESC}} as a way to escape. |
364 | ||
365 | For a state which accepts ordinary Emacs commands, or more generally any | |
366 | kind of state in which @key{ESC} followed by a function key or arrow key | |
367 | is potentially meaningful, then you must not define @kbd{@key{ESC} | |
368 | @key{ESC}}, since that would preclude recognizing an escape sequence | |
369 | after @key{ESC}. In these states, you should define @kbd{@key{ESC} | |
370 | @key{ESC} @key{ESC}} as the way to escape. Otherwise, define | |
371 | @kbd{@key{ESC} @key{ESC}} instead. | |
5e0fc18a | 372 | @end itemize |
52c90d84 | 373 | |
5e0fc18a RS |
374 | @node Programming Tips |
375 | @section Emacs Programming Tips | |
3ff91798 | 376 | |
5e0fc18a RS |
377 | Following these conventions will make your program fit better |
378 | into Emacs when it runs. | |
7015aca4 | 379 | |
5e0fc18a | 380 | @itemize @bullet |
7015aca4 RS |
381 | @item |
382 | Don't use @code{next-line} or @code{previous-line} in programs; nearly | |
383 | always, @code{forward-line} is more convenient as well as more | |
384 | predictable and robust. @xref{Text Lines}. | |
385 | ||
386 | @item | |
574efc83 RS |
387 | Don't call functions that set the mark, unless setting the mark is one |
388 | of the intended features of your program. The mark is a user-level | |
389 | feature, so it is incorrect to change the mark except to supply a value | |
390 | for the user's benefit. @xref{The Mark}. | |
7015aca4 | 391 | |
f9f59935 | 392 | In particular, don't use any of these functions: |
7015aca4 RS |
393 | |
394 | @itemize @bullet | |
395 | @item | |
396 | @code{beginning-of-buffer}, @code{end-of-buffer} | |
397 | @item | |
398 | @code{replace-string}, @code{replace-regexp} | |
5e0fc18a RS |
399 | @item |
400 | @code{insert-file}, @code{insert-buffer} | |
7015aca4 RS |
401 | @end itemize |
402 | ||
5e0fc18a RS |
403 | If you just want to move point, or replace a certain string, or insert |
404 | a file or buffer's contents, without any of the other features | |
405 | intended for interactive users, you can replace these functions with | |
406 | one or two lines of simple Lisp code. | |
7015aca4 | 407 | |
1c2b5877 RS |
408 | @item |
409 | Use lists rather than vectors, except when there is a particular reason | |
410 | to use a vector. Lisp has more facilities for manipulating lists than | |
411 | for vectors, and working with lists is usually more convenient. | |
412 | ||
413 | Vectors are advantageous for tables that are substantial in size and are | |
414 | accessed in random order (not searched front to back), provided there is | |
415 | no need to insert or delete elements (only lists allow that). | |
416 | ||
7015aca4 | 417 | @item |
fb5a74cd | 418 | The recommended way to show a message in the echo area is with |
7015aca4 RS |
419 | the @code{message} function, not @code{princ}. @xref{The Echo Area}. |
420 | ||
421 | @item | |
422 | When you encounter an error condition, call the function @code{error} | |
423 | (or @code{signal}). The function @code{error} does not return. | |
424 | @xref{Signaling Errors}. | |
425 | ||
426 | Do not use @code{message}, @code{throw}, @code{sleep-for}, | |
427 | or @code{beep} to report errors. | |
428 | ||
bfe721d1 KH |
429 | @item |
430 | An error message should start with a capital letter but should not end | |
431 | with a period. | |
432 | ||
f37e0163 RS |
433 | @item |
434 | A question asked in the minibuffer with @code{y-or-n-p} or | |
435 | @code{yes-or-no-p} should start with a capital letter and end with | |
436 | @samp{? }. | |
437 | ||
438 | @item | |
439 | When you mention a default value in a minibuffer prompt, | |
440 | put it and the word @samp{default} inside parentheses. | |
441 | It should look like this: | |
442 | ||
443 | @example | |
090be3b6 | 444 | Enter the answer (default 42): |
f37e0163 RS |
445 | @end example |
446 | ||
01e3636e RS |
447 | @item |
448 | In @code{interactive}, if you use a Lisp expression to produce a list | |
449 | of arguments, don't try to provide the ``correct'' default values for | |
450 | region or position arguments. Instead, provide @code{nil} for those | |
451 | arguments if they were not specified, and have the function body | |
452 | compute the default value when the argument is @code{nil}. For | |
453 | instance, write this: | |
454 | ||
455 | @example | |
456 | (defun foo (pos) | |
457 | (interactive | |
458 | (list (if @var{specified} @var{specified-pos}))) | |
459 | (unless pos (setq pos @var{default-pos})) | |
460 | ...) | |
461 | @end example | |
462 | ||
463 | @noindent | |
464 | rather than this: | |
465 | ||
466 | @example | |
467 | (defun foo (pos) | |
468 | (interactive | |
469 | (list (if @var{specified} @var{specified-pos} | |
470 | @var{default-pos}))) | |
471 | ...) | |
472 | @end example | |
473 | ||
474 | @noindent | |
475 | This is so that repetition of the command will recompute | |
476 | these defaults based on the current circumstances. | |
477 | ||
478 | You do not need to take such precautions when you use interactive | |
479 | specs @samp{d}, @samp{m} and @samp{r}, because they make special | |
480 | arrangements to recompute the argument values on repetition of the | |
481 | command. | |
482 | ||
2089b41a RS |
483 | @item |
484 | Many commands that take a long time to execute display a message that | |
01e3636e | 485 | says something like @samp{Operating...} when they start, and change it to |
2089b41a RS |
486 | @samp{Operating...done} when they finish. Please keep the style of |
487 | these messages uniform: @emph{no} space around the ellipsis, and | |
01e3636e | 488 | @emph{no} period after @samp{done}. |
2089b41a | 489 | |
7015aca4 | 490 | @item |
4b6694ef RS |
491 | Try to avoid using recursive edits. Instead, do what the Rmail @kbd{e} |
492 | command does: use a new local keymap that contains one command defined | |
493 | to switch back to the old local keymap. Or do what the | |
494 | @code{edit-options} command does: switch to another buffer and let the | |
495 | user switch back at will. @xref{Recursive Editing}. | |
7015aca4 RS |
496 | @end itemize |
497 | ||
498 | @node Compilation Tips | |
499 | @section Tips for Making Compiled Code Fast | |
500 | @cindex execution speed | |
501 | @cindex speedups | |
502 | ||
503 | Here are ways of improving the execution speed of byte-compiled | |
4b6694ef | 504 | Lisp programs. |
7015aca4 RS |
505 | |
506 | @itemize @bullet | |
507 | @item | |
508 | @cindex profiling | |
509 | @cindex timing programs | |
a9f0a989 | 510 | @cindex @file{elp.el} |
5f7eb05d EZ |
511 | Profile your program with the @file{elp} library. See the file |
512 | @file{elp.el} for instructions. | |
7015aca4 | 513 | |
6b7abae0 RS |
514 | @item |
515 | @cindex @file{benchmark.el} | |
516 | @cindex benchmarking | |
517 | Check the speed of individual Emacs Lisp forms using the | |
518 | @file{benchmark} library. See the functions @code{benchmark-run} and | |
519 | @code{benchmark-run-compiled} in @file{benchmark.el}. | |
520 | ||
7015aca4 RS |
521 | @item |
522 | Use iteration rather than recursion whenever possible. | |
523 | Function calls are slow in Emacs Lisp even when a compiled function | |
524 | is calling another compiled function. | |
525 | ||
526 | @item | |
bfe721d1 KH |
527 | Using the primitive list-searching functions @code{memq}, @code{member}, |
528 | @code{assq}, or @code{assoc} is even faster than explicit iteration. It | |
f9f59935 | 529 | can be worth rearranging a data structure so that one of these primitive |
bfe721d1 | 530 | search functions can be used. |
7015aca4 RS |
531 | |
532 | @item | |
177c0ea7 | 533 | Certain built-in functions are handled specially in byte-compiled code, |
7015aca4 RS |
534 | avoiding the need for an ordinary function call. It is a good idea to |
535 | use these functions rather than alternatives. To see whether a function | |
536 | is handled specially by the compiler, examine its @code{byte-compile} | |
537 | property. If the property is non-@code{nil}, then the function is | |
538 | handled specially. | |
539 | ||
540 | For example, the following input will show you that @code{aref} is | |
a9f0a989 | 541 | compiled specially (@pxref{Array Functions}): |
7015aca4 | 542 | |
4b6694ef | 543 | @example |
7015aca4 RS |
544 | @group |
545 | (get 'aref 'byte-compile) | |
546 | @result{} byte-compile-two-args | |
547 | @end group | |
4b6694ef | 548 | @end example |
7015aca4 RS |
549 | |
550 | @item | |
1911e6e5 | 551 | If calling a small function accounts for a substantial part of your |
7015aca4 RS |
552 | program's running time, make the function inline. This eliminates |
553 | the function call overhead. Since making a function inline reduces | |
554 | the flexibility of changing the program, don't do it unless it gives | |
4b6694ef | 555 | a noticeable speedup in something slow enough that users care about |
7015aca4 RS |
556 | the speed. @xref{Inline Functions}. |
557 | @end itemize | |
558 | ||
5e0fc18a RS |
559 | @node Warning Tips |
560 | @section Tips for Avoiding Compiler Warnings | |
561 | ||
562 | @itemize @bullet | |
563 | @item | |
564 | Try to avoid compiler warnings about undefined free variables, by adding | |
565 | dummy @code{defvar} definitions for these variables, like this: | |
566 | ||
567 | @example | |
568 | (defvar foo) | |
569 | @end example | |
570 | ||
571 | Such a definition has no effect except to tell the compiler | |
572 | not to warn about uses of the variable @code{foo} in this file. | |
573 | ||
574 | @item | |
575 | If you use many functions and variables from a certain file, you can | |
576 | add a @code{require} for that package to avoid compilation warnings | |
577 | for them. For instance, | |
578 | ||
579 | @example | |
580 | (eval-when-compile | |
581 | (require 'foo)) | |
582 | @end example | |
583 | ||
584 | @item | |
585 | If you bind a variable in one function, and use it or set it in | |
586 | another function, the compiler warns about the latter function unless | |
587 | the variable has a definition. But adding a definition would be | |
588 | unclean if the variable has a short name, since Lisp packages should | |
589 | not define short variable names. The right thing to do is to rename | |
590 | this variable to start with the name prefix used for the other | |
591 | functions and variables in your package. | |
592 | ||
593 | @item | |
594 | The last resort for avoiding a warning, when you want to do something | |
595 | that usually is a mistake but it's not a mistake in this one case, | |
596 | is to put a call to @code{with-no-warnings} around it. | |
597 | @end itemize | |
598 | ||
7015aca4 RS |
599 | @node Documentation Tips |
600 | @section Tips for Documentation Strings | |
601 | ||
969fe9b5 RS |
602 | @findex checkdoc-minor-mode |
603 | Here are some tips and conventions for the writing of documentation | |
604 | strings. You can check many of these conventions by running the command | |
605 | @kbd{M-x checkdoc-minor-mode}. | |
7015aca4 RS |
606 | |
607 | @itemize @bullet | |
608 | @item | |
574efc83 | 609 | Every command, function, or variable intended for users to know about |
7015aca4 RS |
610 | should have a documentation string. |
611 | ||
612 | @item | |
e0d32668 RS |
613 | An internal variable or subroutine of a Lisp program might as well have |
614 | a documentation string. In earlier Emacs versions, you could save space | |
615 | by using a comment instead of a documentation string, but that is no | |
2468d0c0 DL |
616 | longer the case---documentation strings now take up very little space in |
617 | a running Emacs. | |
7015aca4 | 618 | |
b090d792 RS |
619 | @item |
620 | Format the documentation string so that it fits in an Emacs window on an | |
621 | 80-column screen. It is a good idea for most lines to be no wider than | |
622 | 60 characters. The first line should not be wider than 67 characters | |
623 | or it will look bad in the output of @code{apropos}. | |
624 | ||
625 | You can fill the text if that looks good. However, rather than blindly | |
626 | filling the entire documentation string, you can often make it much more | |
627 | readable by choosing certain line breaks with care. Use blank lines | |
628 | between topics if the documentation string is long. | |
629 | ||
7015aca4 RS |
630 | @item |
631 | The first line of the documentation string should consist of one or two | |
574efc83 | 632 | complete sentences that stand on their own as a summary. @kbd{M-x |
2468d0c0 DL |
633 | apropos} displays just the first line, and if that line's contents don't |
634 | stand on their own, the result looks bad. In particular, start the | |
635 | first line with a capital letter and end with a period. | |
7015aca4 | 636 | |
aa5dbf7b RS |
637 | For a function, the first line should briefly answer the question, |
638 | ``What does this function do?'' For a variable, the first line should | |
639 | briefly answer the question, ``What does this value mean?'' | |
640 | ||
641 | Don't limit the documentation string to one line; use as many lines as | |
642 | you need to explain the details of how to use the function or | |
643 | variable. Please use complete sentences for the rest of the text too. | |
7015aca4 | 644 | |
7878d6b6 RS |
645 | @item |
646 | The first line should mention all the important arguments of the | |
647 | function, and should mention them in the order that they are written | |
648 | in a function call. If the function has many arguments, then it is | |
649 | not feasible to mention them all in the first line; in that case, the | |
650 | first line should mention the first few arguments, including the most | |
651 | important arguments. | |
652 | ||
4b6694ef | 653 | @item |
8241495d | 654 | For consistency, phrase the verb in the first sentence of a function's |
321a3725 | 655 | documentation string as an imperative---for instance, use ``Return the |
8241495d RS |
656 | cons of A and B.'' in preference to ``Returns the cons of A and B@.'' |
657 | Usually it looks good to do likewise for the rest of the first | |
658 | paragraph. Subsequent paragraphs usually look better if each sentence | |
b090d792 | 659 | is indicative and has a proper subject. |
4b6694ef | 660 | |
7015aca4 RS |
661 | @item |
662 | Write documentation strings in the active voice, not the passive, and in | |
663 | the present tense, not the future. For instance, use ``Return a list | |
664 | containing A and B.'' instead of ``A list containing A and B will be | |
665 | returned.'' | |
666 | ||
667 | @item | |
668 | Avoid using the word ``cause'' (or its equivalents) unnecessarily. | |
669 | Instead of, ``Cause Emacs to display text in boldface,'' write just | |
670 | ``Display text in boldface.'' | |
671 | ||
2468d0c0 DL |
672 | @item |
673 | When a command is meaningful only in a certain mode or situation, | |
674 | do mention that in the documentation string. For example, | |
675 | the documentation of @code{dired-find-file} is: | |
676 | ||
677 | @example | |
678 | In Dired, visit the file or directory named on this line. | |
679 | @end example | |
680 | ||
7015aca4 RS |
681 | @item |
682 | Do not start or end a documentation string with whitespace. | |
177c0ea7 | 683 | |
7015aca4 RS |
684 | @item |
685 | @strong{Do not} indent subsequent lines of a documentation string so | |
686 | that the text is lined up in the source code with the text of the first | |
687 | line. This looks nice in the source code, but looks bizarre when users | |
688 | view the documentation. Remember that the indentation before the | |
689 | starting double-quote is not part of the string! | |
690 | ||
75d97f47 RS |
691 | @item |
692 | When the user tries to use a disabled command, Emacs displays just the | |
693 | first paragraph of its documentation string---everything through the | |
694 | first blank line. If you wish, you can choose which information to | |
695 | include before the first blank line so as to make this display useful. | |
696 | ||
7015aca4 | 697 | @item |
eef4e174 | 698 | When you define a variable that users ought to set interactively, you |
d8ea07f6 | 699 | normally should use @code{defcustom}. However, if for some reason you |
eef4e174 LT |
700 | use @code{defvar} instead, start the doc string with a @samp{*}. |
701 | @xref{Defining Variables}. | |
7015aca4 RS |
702 | |
703 | @item | |
704 | The documentation string for a variable that is a yes-or-no flag should | |
827b7ee7 | 705 | start with words such as ``Non-nil means,'' to make it clear that |
4b6694ef RS |
706 | all non-@code{nil} values are equivalent and indicate explicitly what |
707 | @code{nil} and non-@code{nil} mean. | |
7015aca4 | 708 | |
5c5b7d3e RS |
709 | @item |
710 | The documentation string for a function that is a yes-or-no predicate | |
827b7ee7 RS |
711 | should start with words such as ``Return t if,'' to indicate |
712 | explicitly what constitutes ``truth.'' The word ``return'' avoids | |
713 | starting the sentence with lower-case ``t,'' which could be somewhat | |
5c5b7d3e RS |
714 | distracting. |
715 | ||
7015aca4 RS |
716 | @item |
717 | When a function's documentation string mentions the value of an argument | |
718 | of the function, use the argument name in capital letters as if it were | |
719 | a name for that value. Thus, the documentation string of the function | |
2468d0c0 DL |
720 | @code{eval} refers to its second argument as @samp{FORM}, because the |
721 | actual argument name is @code{form}: | |
722 | ||
723 | @example | |
724 | Evaluate FORM and return its value. | |
725 | @end example | |
7015aca4 | 726 | |
2468d0c0 DL |
727 | Also write metasyntactic variables in capital letters, such as when you |
728 | show the decomposition of a list or vector into subunits, some of which | |
729 | may vary. @samp{KEY} and @samp{VALUE} in the following example | |
8241495d RS |
730 | illustrate this practice: |
731 | ||
732 | @example | |
733 | The argument TABLE should be an alist whose elements | |
734 | have the form (KEY . VALUE). Here, KEY is ... | |
735 | @end example | |
7015aca4 | 736 | |
5c5b7d3e RS |
737 | @item |
738 | Never change the case of a Lisp symbol when you mention it in a doc | |
827b7ee7 | 739 | string. If the symbol's name is @code{foo}, write ``foo,'' not |
5c5b7d3e RS |
740 | ``Foo'' (which is a different symbol). |
741 | ||
742 | This might appear to contradict the policy of writing function | |
743 | argument values, but there is no real contradiction; the argument | |
744 | @emph{value} is not the same thing as the @emph{symbol} which the | |
745 | function uses to hold the value. | |
746 | ||
747 | If this puts a lower-case letter at the beginning of a sentence | |
748 | and that annoys you, rewrite the sentence so that the symbol | |
749 | is not at the start of it. | |
750 | ||
2468d0c0 DL |
751 | @item |
752 | If a line in a documentation string begins with an open-parenthesis, | |
753 | write a backslash before the open-parenthesis, like this: | |
754 | ||
755 | @example | |
756 | The argument FOO can be either a number | |
757 | \(a buffer position) or a string (a file name). | |
758 | @end example | |
759 | ||
760 | This prevents the open-parenthesis from being treated as the start of a | |
761 | defun (@pxref{Defuns,, Defuns, emacs, The GNU Emacs Manual}). | |
762 | ||
70057f39 | 763 | @anchor{Docstring hyperlinks} |
7015aca4 RS |
764 | @item |
765 | @iftex | |
766 | When a documentation string refers to a Lisp symbol, write it as it | |
767 | would be printed (which usually means in lower case), with single-quotes | |
768 | around it. For example: @samp{`lambda'}. There are two exceptions: | |
769 | write @code{t} and @code{nil} without single-quotes. | |
770 | @end iftex | |
37680279 | 771 | @ifnottex |
7015aca4 RS |
772 | When a documentation string refers to a Lisp symbol, write it as it |
773 | would be printed (which usually means in lower case), with single-quotes | |
774 | around it. For example: @samp{lambda}. There are two exceptions: write | |
969fe9b5 RS |
775 | t and nil without single-quotes. (In this manual, we use a different |
776 | convention, with single-quotes for all symbols.) | |
37680279 | 777 | @end ifnottex |
7015aca4 | 778 | |
1911e6e5 RS |
779 | Help mode automatically creates a hyperlink when a documentation string |
780 | uses a symbol name inside single quotes, if the symbol has either a | |
a9f0a989 RS |
781 | function or a variable definition. You do not need to do anything |
782 | special to make use of this feature. However, when a symbol has both a | |
783 | function definition and a variable definition, and you want to refer to | |
784 | just one of them, you can specify which one by writing one of the words | |
785 | @samp{variable}, @samp{option}, @samp{function}, or @samp{command}, | |
786 | immediately before the symbol name. (Case makes no difference in | |
787 | recognizing these indicator words.) For example, if you write | |
788 | ||
789 | @example | |
790 | This function sets the variable `buffer-file-name'. | |
791 | @end example | |
792 | ||
793 | @noindent | |
794 | then the hyperlink will refer only to the variable documentation of | |
795 | @code{buffer-file-name}, and not to its function documentation. | |
796 | ||
797 | If a symbol has a function definition and/or a variable definition, but | |
798 | those are irrelevant to the use of the symbol that you are documenting, | |
7f681212 LT |
799 | you can write the words @samp{symbol} or @samp{program} before the |
800 | symbol name to prevent making any hyperlink. For example, | |
969fe9b5 RS |
801 | |
802 | @example | |
a9f0a989 RS |
803 | If the argument KIND-OF-RESULT is the symbol `list', |
804 | this function returns a list of all the objects | |
805 | that satisfy the criterion. | |
969fe9b5 RS |
806 | @end example |
807 | ||
a9f0a989 RS |
808 | @noindent |
809 | does not make a hyperlink to the documentation, irrelevant here, of the | |
810 | function @code{list}. | |
811 | ||
e72850d5 LT |
812 | Normally, no hyperlink is made for a variable without variable |
813 | documentation. You can force a hyperlink for such variables by | |
814 | preceding them with one of the words @samp{variable} or | |
815 | @samp{option}. | |
816 | ||
817 | Hyperlinks for faces are only made if the face name is preceded or | |
818 | followed by the word @samp{face}. In that case, only the face | |
819 | documentation will be shown, even if the symbol is also defined as a | |
820 | variable or as a function. | |
821 | ||
8241495d | 822 | To make a hyperlink to Info documentation, write the name of the Info |
727c9159 LT |
823 | node (or anchor) in single quotes, preceded by @samp{info node}, |
824 | @samp{Info node}, @samp{info anchor} or @samp{Info anchor}. The Info | |
825 | file name defaults to @samp{emacs}. For example, | |
8241495d RS |
826 | |
827 | @smallexample | |
828 | See Info node `Font Lock' and Info node `(elisp)Font Lock Basics'. | |
829 | @end smallexample | |
830 | ||
7000848e BW |
831 | Finally, to create a hyperlink to URLs, write the URL in single |
832 | quotes, preceded by @samp{URL}. For example, | |
833 | ||
834 | @smallexample | |
835 | The home page for the GNU project has more information (see URL | |
836 | `http://www.gnu.org/'). | |
837 | @end smallexample | |
838 | ||
7015aca4 RS |
839 | @item |
840 | Don't write key sequences directly in documentation strings. Instead, | |
841 | use the @samp{\\[@dots{}]} construct to stand for them. For example, | |
9e2b495b RS |
842 | instead of writing @samp{C-f}, write the construct |
843 | @samp{\\[forward-char]}. When Emacs displays the documentation string, | |
844 | it substitutes whatever key is currently bound to @code{forward-char}. | |
845 | (This is normally @samp{C-f}, but it may be some other character if the | |
846 | user has moved key bindings.) @xref{Keys in Documentation}. | |
7015aca4 RS |
847 | |
848 | @item | |
849 | In documentation strings for a major mode, you will want to refer to the | |
850 | key bindings of that mode's local map, rather than global ones. | |
851 | Therefore, use the construct @samp{\\<@dots{}>} once in the | |
852 | documentation string to specify which key map to use. Do this before | |
853 | the first use of @samp{\\[@dots{}]}. The text inside the | |
854 | @samp{\\<@dots{}>} should be the name of the variable containing the | |
855 | local keymap for the major mode. | |
856 | ||
857 | It is not practical to use @samp{\\[@dots{}]} very many times, because | |
858 | display of the documentation string will become slow. So use this to | |
859 | describe the most important commands in your major mode, and then use | |
860 | @samp{\\@{@dots{}@}} to display the rest of the mode's keymap. | |
7015aca4 RS |
861 | @end itemize |
862 | ||
863 | @node Comment Tips | |
864 | @section Tips on Writing Comments | |
865 | ||
866 | We recommend these conventions for where to put comments and how to | |
867 | indent them: | |
868 | ||
869 | @table @samp | |
870 | @item ; | |
871 | Comments that start with a single semicolon, @samp{;}, should all be | |
872 | aligned to the same column on the right of the source code. Such | |
873 | comments usually explain how the code on the same line does its job. In | |
874 | Lisp mode and related modes, the @kbd{M-;} (@code{indent-for-comment}) | |
875 | command automatically inserts such a @samp{;} in the right place, or | |
4b6694ef | 876 | aligns such a comment if it is already present. |
7015aca4 | 877 | |
574efc83 | 878 | This and following examples are taken from the Emacs sources. |
7015aca4 RS |
879 | |
880 | @smallexample | |
881 | @group | |
882 | (setq base-version-list ; there was a base | |
883 | (assoc (substring fn 0 start-vn) ; version to which | |
884 | file-version-assoc-list)) ; this looks like | |
885 | ; a subversion | |
886 | @end group | |
887 | @end smallexample | |
888 | ||
889 | @item ;; | |
890 | Comments that start with two semicolons, @samp{;;}, should be aligned to | |
4b6694ef | 891 | the same level of indentation as the code. Such comments usually |
7015aca4 RS |
892 | describe the purpose of the following lines or the state of the program |
893 | at that point. For example: | |
894 | ||
895 | @smallexample | |
896 | @group | |
897 | (prog1 (setq auto-fill-function | |
898 | @dots{} | |
899 | @dots{} | |
4b6694ef | 900 | ;; update mode line |
7015aca4 RS |
901 | (force-mode-line-update))) |
902 | @end group | |
903 | @end smallexample | |
904 | ||
2468d0c0 | 905 | We also normally use two semicolons for comments outside functions. |
7015aca4 RS |
906 | |
907 | @smallexample | |
908 | @group | |
2468d0c0 DL |
909 | ;; This Lisp code is run in Emacs |
910 | ;; when it is to operate as a server | |
911 | ;; for other processes. | |
7015aca4 RS |
912 | @end group |
913 | @end smallexample | |
914 | ||
2468d0c0 DL |
915 | Every function that has no documentation string (presumably one that is |
916 | used only internally within the package it belongs to), should instead | |
917 | have a two-semicolon comment right before the function, explaining what | |
918 | the function does and how to call it properly. Explain precisely what | |
919 | each argument means and how the function interprets its possible values. | |
920 | ||
921 | @item ;;; | |
922 | Comments that start with three semicolons, @samp{;;;}, should start at | |
923 | the left margin. These are used, occasionally, for comments within | |
924 | functions that should start at the margin. We also use them sometimes | |
925 | for comments that are between functions---whether to use two or three | |
dd4a1d28 LT |
926 | semicolons depends on whether the comment should be considered a |
927 | ``heading'' by Outline minor mode. By default, comments starting with | |
928 | at least three semicolons (followed by a single space and a | |
929 | non-whitespace character) are considered headings, comments starting | |
930 | with two or less are not. | |
2468d0c0 | 931 | |
574efc83 | 932 | Another use for triple-semicolon comments is for commenting out lines |
2468d0c0 | 933 | within a function. We use three semicolons for this precisely so that |
dd4a1d28 LT |
934 | they remain at the left margin. By default, Outline minor mode does |
935 | not consider a comment to be a heading (even if it starts with at | |
936 | least three semicolons) if the semicolons are followed by at least two | |
937 | spaces. Thus, if you add an introductory comment to the commented out | |
938 | code, make sure to indent it by at least two spaces after the three | |
939 | semicolons. | |
4b6694ef RS |
940 | |
941 | @smallexample | |
942 | (defun foo (a) | |
dd4a1d28 | 943 | ;;; This is no longer necessary. |
4b6694ef RS |
944 | ;;; (force-mode-line-update) |
945 | (message "Finished with %s" a)) | |
946 | @end smallexample | |
947 | ||
dd4a1d28 LT |
948 | When commenting out entire functions, use two semicolons. |
949 | ||
7015aca4 RS |
950 | @item ;;;; |
951 | Comments that start with four semicolons, @samp{;;;;}, should be aligned | |
952 | to the left margin and are used for headings of major sections of a | |
953 | program. For example: | |
954 | ||
955 | @smallexample | |
956 | ;;;; The kill ring | |
957 | @end smallexample | |
958 | @end table | |
959 | ||
960 | @noindent | |
961 | The indentation commands of the Lisp modes in Emacs, such as @kbd{M-;} | |
969fe9b5 | 962 | (@code{indent-for-comment}) and @key{TAB} (@code{lisp-indent-line}), |
7015aca4 | 963 | automatically indent comments according to these conventions, |
574efc83 | 964 | depending on the number of semicolons. @xref{Comments,, |
7015aca4 RS |
965 | Manipulating Comments, emacs, The GNU Emacs Manual}. |
966 | ||
7015aca4 RS |
967 | @node Library Headers |
968 | @section Conventional Headers for Emacs Libraries | |
969 | @cindex header comments | |
970 | @cindex library header comments | |
971 | ||
f9f59935 | 972 | Emacs has conventions for using special comments in Lisp libraries |
7015aca4 | 973 | to divide them into sections and give information such as who wrote |
8241495d RS |
974 | them. This section explains these conventions. |
975 | ||
976 | We'll start with an example, a package that is included in the Emacs | |
977 | distribution. | |
978 | ||
979 | Parts of this example reflect its status as part of Emacs; for | |
980 | example, the copyright notice lists the Free Software Foundation as the | |
981 | copyright holder, and the copying permission says the file is part of | |
982 | Emacs. When you write a package and post it, the copyright holder would | |
983 | be you (unless your employer claims to own it instead), and you should | |
984 | get the suggested copying permission from the end of the GNU General | |
985 | Public License itself. Don't say your file is part of Emacs | |
986 | if we haven't installed it in Emacs yet! | |
987 | ||
988 | With that warning out of the way, on to the example: | |
7015aca4 RS |
989 | |
990 | @smallexample | |
991 | @group | |
992 | ;;; lisp-mnt.el --- minor mode for Emacs Lisp maintainers | |
993 | ||
994 | ;; Copyright (C) 1992 Free Software Foundation, Inc. | |
995 | @end group | |
996 | ||
997 | ;; Author: Eric S. Raymond <esr@@snark.thyrsus.com> | |
998 | ;; Maintainer: Eric S. Raymond <esr@@snark.thyrsus.com> | |
999 | ;; Created: 14 Jul 1992 | |
1000 | ;; Version: 1.2 | |
1001 | @group | |
1002 | ;; Keywords: docs | |
1003 | ||
1004 | ;; This file is part of GNU Emacs. | |
969fe9b5 | 1005 | @dots{} |
086add15 LK |
1006 | ;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, |
1007 | ;; Boston, MA 02110-1301, USA. | |
7015aca4 RS |
1008 | @end group |
1009 | @end smallexample | |
1010 | ||
1011 | The very first line should have this format: | |
1012 | ||
1013 | @example | |
1014 | ;;; @var{filename} --- @var{description} | |
1015 | @end example | |
1016 | ||
1017 | @noindent | |
e4317c8c RS |
1018 | The description should be complete in one line. If the file |
1019 | needs a @samp{-*-} specification, put it after @var{description}. | |
7015aca4 RS |
1020 | |
1021 | After the copyright notice come several @dfn{header comment} lines, | |
4b6694ef | 1022 | each beginning with @samp{;; @var{header-name}:}. Here is a table of |
7015aca4 RS |
1023 | the conventional possibilities for @var{header-name}: |
1024 | ||
1025 | @table @samp | |
1026 | @item Author | |
1027 | This line states the name and net address of at least the principal | |
1028 | author of the library. | |
1029 | ||
1030 | If there are multiple authors, you can list them on continuation lines | |
4b6694ef | 1031 | led by @code{;;} and a tab character, like this: |
7015aca4 RS |
1032 | |
1033 | @smallexample | |
1034 | @group | |
1035 | ;; Author: Ashwin Ram <Ram-Ashwin@@cs.yale.edu> | |
4b6694ef RS |
1036 | ;; Dave Sill <de5@@ornl.gov> |
1037 | ;; Dave Brennan <brennan@@hal.com> | |
1038 | ;; Eric Raymond <esr@@snark.thyrsus.com> | |
7015aca4 RS |
1039 | @end group |
1040 | @end smallexample | |
1041 | ||
1042 | @item Maintainer | |
1043 | This line should contain a single name/address as in the Author line, or | |
4b6694ef RS |
1044 | an address only, or the string @samp{FSF}. If there is no maintainer |
1045 | line, the person(s) in the Author field are presumed to be the | |
1046 | maintainers. The example above is mildly bogus because the maintainer | |
1047 | line is redundant. | |
7015aca4 RS |
1048 | |
1049 | The idea behind the @samp{Author} and @samp{Maintainer} lines is to make | |
1050 | possible a Lisp function to ``send mail to the maintainer'' without | |
1051 | having to mine the name out by hand. | |
1052 | ||
1053 | Be sure to surround the network address with @samp{<@dots{}>} if | |
1054 | you include the person's full name as well as the network address. | |
1055 | ||
1056 | @item Created | |
1057 | This optional line gives the original creation date of the | |
1058 | file. For historical interest only. | |
1059 | ||
1060 | @item Version | |
1061 | If you wish to record version numbers for the individual Lisp program, put | |
1062 | them in this line. | |
1063 | ||
1064 | @item Adapted-By | |
1065 | In this header line, place the name of the person who adapted the | |
1066 | library for installation (to make it fit the style conventions, for | |
1067 | example). | |
1068 | ||
1069 | @item Keywords | |
1070 | This line lists keywords for the @code{finder-by-keyword} help command. | |
a9f0a989 RS |
1071 | Please use that command to see a list of the meaningful keywords. |
1072 | ||
7015aca4 | 1073 | This field is important; it's how people will find your package when |
2c62739d RS |
1074 | they're looking for things by topic area. To separate the keywords, you |
1075 | can use spaces, commas, or both. | |
7015aca4 RS |
1076 | @end table |
1077 | ||
1078 | Just about every Lisp library ought to have the @samp{Author} and | |
1079 | @samp{Keywords} header comment lines. Use the others if they are | |
1080 | appropriate. You can also put in header lines with other header | |
1081 | names---they have no standard meanings, so they can't do any harm. | |
1082 | ||
1083 | We use additional stylized comments to subdivide the contents of the | |
2468d0c0 DL |
1084 | library file. These should be separated by blank lines from anything |
1085 | else. Here is a table of them: | |
7015aca4 RS |
1086 | |
1087 | @table @samp | |
1088 | @item ;;; Commentary: | |
1089 | This begins introductory comments that explain how the library works. | |
a9f0a989 RS |
1090 | It should come right after the copying permissions, terminated by a |
1091 | @samp{Change Log}, @samp{History} or @samp{Code} comment line. This | |
1092 | text is used by the Finder package, so it should make sense in that | |
1093 | context. | |
1094 | ||
fd423b79 | 1095 | @item ;;; Documentation: |
3ff91798 RS |
1096 | This was used in some files in place of @samp{;;; Commentary:}, |
1097 | but it is deprecated. | |
7015aca4 | 1098 | |
a9f0a989 | 1099 | @item ;;; Change Log: |
7015aca4 | 1100 | This begins change log information stored in the library file (if you |
2468d0c0 DL |
1101 | store the change history there). For Lisp files distributed with Emacs, |
1102 | the change history is kept in the file @file{ChangeLog} and not in the | |
1103 | source file at all; these files generally do not have a @samp{;;; Change | |
1104 | Log:} line. @samp{History} is an alternative to @samp{Change Log}. | |
7015aca4 RS |
1105 | |
1106 | @item ;;; Code: | |
1107 | This begins the actual code of the program. | |
1108 | ||
1109 | @item ;;; @var{filename} ends here | |
1110 | This is the @dfn{footer line}; it appears at the very end of the file. | |
1111 | Its purpose is to enable people to detect truncated versions of the file | |
1112 | from the lack of a footer line. | |
1113 | @end table | |
ab5796a9 MB |
1114 | |
1115 | @ignore | |
1116 | arch-tag: 9ea911c2-6b1d-47dd-88b7-0a94e8b27c2e | |
1117 | @end ignore |