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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
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3 | @c Copyright (C) 1990-1995, 1998-1999, 2001-2013 Free Software |
4 | @c Foundation, Inc. | |
b8d4c8d0 | 5 | @c See the file elisp.texi for copying conditions. |
ecc6530d | 6 | @node Loading |
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7 | @chapter Loading |
8 | @cindex loading | |
9 | @cindex library | |
10 | @cindex Lisp library | |
11 | ||
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12 | Loading a file of Lisp code means bringing its contents into the |
13 | Lisp environment in the form of Lisp objects. Emacs finds and opens | |
14 | the file, reads the text, evaluates each form, and then closes the | |
15 | file. Such a file is also called a @dfn{Lisp library}. | |
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16 | |
17 | The load functions evaluate all the expressions in a file just | |
18 | as the @code{eval-buffer} function evaluates all the | |
19 | expressions in a buffer. The difference is that the load functions | |
20 | read and evaluate the text in the file as found on disk, not the text | |
21 | in an Emacs buffer. | |
22 | ||
23 | @cindex top-level form | |
24 | The loaded file must contain Lisp expressions, either as source code | |
25 | or as byte-compiled code. Each form in the file is called a | |
26 | @dfn{top-level form}. There is no special format for the forms in a | |
27 | loadable file; any form in a file may equally well be typed directly | |
28 | into a buffer and evaluated there. (Indeed, most code is tested this | |
29 | way.) Most often, the forms are function definitions and variable | |
30 | definitions. | |
31 | ||
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32 | @menu |
33 | * How Programs Do Loading:: The @code{load} function and others. | |
34 | * Load Suffixes:: Details about the suffixes that @code{load} tries. | |
35 | * Library Search:: Finding a library to load. | |
36 | * Loading Non-ASCII:: Non-@acronym{ASCII} characters in Emacs Lisp files. | |
37 | * Autoload:: Setting up a function to autoload. | |
38 | * Repeated Loading:: Precautions about loading a file twice. | |
39 | * Named Features:: Loading a library if it isn't already loaded. | |
40 | * Where Defined:: Finding which file defined a certain symbol. | |
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41 | * Unloading:: How to "unload" a library that was loaded. |
42 | * Hooks for Loading:: Providing code to be run when | |
43 | particular libraries are loaded. | |
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44 | @end menu |
45 | ||
46 | @node How Programs Do Loading | |
47 | @section How Programs Do Loading | |
48 | ||
49 | Emacs Lisp has several interfaces for loading. For example, | |
50 | @code{autoload} creates a placeholder object for a function defined in a | |
51 | file; trying to call the autoloading function loads the file to get the | |
52 | function's real definition (@pxref{Autoload}). @code{require} loads a | |
53 | file if it isn't already loaded (@pxref{Named Features}). Ultimately, | |
54 | all these facilities call the @code{load} function to do the work. | |
55 | ||
56 | @defun load filename &optional missing-ok nomessage nosuffix must-suffix | |
57 | This function finds and opens a file of Lisp code, evaluates all the | |
58 | forms in it, and closes the file. | |
59 | ||
60 | To find the file, @code{load} first looks for a file named | |
61 | @file{@var{filename}.elc}, that is, for a file whose name is | |
62 | @var{filename} with the extension @samp{.elc} appended. If such a | |
63 | file exists, it is loaded. If there is no file by that name, then | |
64 | @code{load} looks for a file named @file{@var{filename}.el}. If that | |
65 | file exists, it is loaded. Finally, if neither of those names is | |
66 | found, @code{load} looks for a file named @var{filename} with nothing | |
67 | appended, and loads it if it exists. (The @code{load} function is not | |
68 | clever about looking at @var{filename}. In the perverse case of a | |
69 | file named @file{foo.el.el}, evaluation of @code{(load "foo.el")} will | |
70 | indeed find it.) | |
71 | ||
72 | If Auto Compression mode is enabled, as it is by default, then if | |
73 | @code{load} can not find a file, it searches for a compressed version | |
74 | of the file before trying other file names. It decompresses and loads | |
75 | it if it exists. It looks for compressed versions by appending each | |
76 | of the suffixes in @code{jka-compr-load-suffixes} to the file name. | |
77 | The value of this variable must be a list of strings. Its standard | |
78 | value is @code{(".gz")}. | |
79 | ||
80 | If the optional argument @var{nosuffix} is non-@code{nil}, then | |
81 | @code{load} does not try the suffixes @samp{.elc} and @samp{.el}. In | |
82 | this case, you must specify the precise file name you want, except | |
83 | that, if Auto Compression mode is enabled, @code{load} will still use | |
84 | @code{jka-compr-load-suffixes} to find compressed versions. By | |
85 | specifying the precise file name and using @code{t} for | |
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86 | @var{nosuffix}, you can prevent file names like @file{foo.el.el} from |
87 | being tried. | |
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88 | |
89 | If the optional argument @var{must-suffix} is non-@code{nil}, then | |
90 | @code{load} insists that the file name used must end in either | |
91 | @samp{.el} or @samp{.elc} (possibly extended with a compression | |
92 | suffix), unless it contains an explicit directory name. | |
93 | ||
94 | If @var{filename} is a relative file name, such as @file{foo} or | |
95 | @file{baz/foo.bar}, @code{load} searches for the file using the variable | |
96 | @code{load-path}. It appends @var{filename} to each of the directories | |
97 | listed in @code{load-path}, and loads the first file it finds whose name | |
98 | matches. The current default directory is tried only if it is specified | |
99 | in @code{load-path}, where @code{nil} stands for the default directory. | |
100 | @code{load} tries all three possible suffixes in the first directory in | |
101 | @code{load-path}, then all three suffixes in the second directory, and | |
102 | so on. @xref{Library Search}. | |
103 | ||
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104 | Whatever the name under which the file is eventually found, and the |
105 | directory where Emacs found it, Emacs sets the value of the variable | |
106 | @code{load-file-name} to that file's name. | |
107 | ||
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108 | If you get a warning that @file{foo.elc} is older than @file{foo.el}, it |
109 | means you should consider recompiling @file{foo.el}. @xref{Byte | |
110 | Compilation}. | |
111 | ||
112 | When loading a source file (not compiled), @code{load} performs | |
113 | character set translation just as Emacs would do when visiting the file. | |
114 | @xref{Coding Systems}. | |
115 | ||
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116 | @c This is referred to from the Macros chapter. |
117 | @c Not sure if it should be the other way round. | |
118 | @cindex eager macro expansion | |
119 | When loading an uncompiled file, Emacs tries to expand any macros | |
120 | that the file contains (@pxref{Macros}). We refer to this as | |
121 | @dfn{eager macro expansion}. Doing this (rather than deferring | |
122 | the expansion until the relevant code runs) can significantly speed | |
123 | up the execution of uncompiled code. Sometimes, this macro expansion | |
124 | cannot be done, owing to a cyclic dependency. In the simplest | |
125 | example of this, the file you are loading refers to a macro defined | |
126 | in another file, and that file in turn requires the file you are | |
127 | loading. This is generally harmless. Emacs prints a warning | |
128 | (@samp{Eager macro-expansion skipped due to cycle@dots{}}) | |
129 | giving details of the problem, but it still loads the file, just | |
130 | leaving the macro unexpanded for now. You may wish to restructure | |
131 | your code so that this does not happen. Loading a compiled file does | |
132 | not cause macroexpansion, because this should already have happened | |
133 | during compilation. @xref{Compiling Macros}. | |
134 | ||
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135 | Messages like @samp{Loading foo...} and @samp{Loading foo...done} appear |
136 | in the echo area during loading unless @var{nomessage} is | |
137 | non-@code{nil}. | |
138 | ||
139 | @cindex load errors | |
140 | Any unhandled errors while loading a file terminate loading. If the | |
141 | load was done for the sake of @code{autoload}, any function definitions | |
142 | made during the loading are undone. | |
143 | ||
144 | @kindex file-error | |
145 | If @code{load} can't find the file to load, then normally it signals the | |
146 | error @code{file-error} (with @samp{Cannot open load file | |
147 | @var{filename}}). But if @var{missing-ok} is non-@code{nil}, then | |
148 | @code{load} just returns @code{nil}. | |
149 | ||
150 | You can use the variable @code{load-read-function} to specify a function | |
151 | for @code{load} to use instead of @code{read} for reading expressions. | |
152 | See below. | |
153 | ||
154 | @code{load} returns @code{t} if the file loads successfully. | |
155 | @end defun | |
156 | ||
157 | @deffn Command load-file filename | |
158 | This command loads the file @var{filename}. If @var{filename} is a | |
159 | relative file name, then the current default directory is assumed. | |
160 | This command does not use @code{load-path}, and does not append | |
161 | suffixes. However, it does look for compressed versions (if Auto | |
162 | Compression Mode is enabled). Use this command if you wish to specify | |
163 | precisely the file name to load. | |
164 | @end deffn | |
165 | ||
166 | @deffn Command load-library library | |
167 | This command loads the library named @var{library}. It is equivalent to | |
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168 | @code{load}, except for the way it reads its argument interactively. |
169 | @xref{Lisp Libraries,,,emacs, The GNU Emacs Manual}. | |
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170 | @end deffn |
171 | ||
172 | @defvar load-in-progress | |
173 | This variable is non-@code{nil} if Emacs is in the process of loading a | |
174 | file, and it is @code{nil} otherwise. | |
175 | @end defvar | |
176 | ||
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177 | @defvar load-file-name |
178 | When Emacs is in the process of loading a file, this variable's value | |
179 | is the name of that file, as Emacs found it during the search | |
180 | described earlier in this section. | |
181 | @end defvar | |
182 | ||
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183 | @defvar load-read-function |
184 | @anchor{Definition of load-read-function} | |
185 | @c do not allow page break at anchor; work around Texinfo deficiency. | |
186 | This variable specifies an alternate expression-reading function for | |
187 | @code{load} and @code{eval-region} to use instead of @code{read}. | |
188 | The function should accept one argument, just as @code{read} does. | |
189 | ||
190 | Normally, the variable's value is @code{nil}, which means those | |
191 | functions should use @code{read}. | |
192 | ||
193 | Instead of using this variable, it is cleaner to use another, newer | |
194 | feature: to pass the function as the @var{read-function} argument to | |
195 | @code{eval-region}. @xref{Definition of eval-region,, Eval}. | |
196 | @end defvar | |
197 | ||
198 | For information about how @code{load} is used in building Emacs, see | |
199 | @ref{Building Emacs}. | |
200 | ||
201 | @node Load Suffixes | |
202 | @section Load Suffixes | |
203 | We now describe some technical details about the exact suffixes that | |
204 | @code{load} tries. | |
205 | ||
206 | @defvar load-suffixes | |
207 | This is a list of suffixes indicating (compiled or source) Emacs Lisp | |
208 | files. It should not include the empty string. @code{load} uses | |
209 | these suffixes in order when it appends Lisp suffixes to the specified | |
210 | file name. The standard value is @code{(".elc" ".el")} which produces | |
211 | the behavior described in the previous section. | |
212 | @end defvar | |
213 | ||
214 | @defvar load-file-rep-suffixes | |
215 | This is a list of suffixes that indicate representations of the same | |
216 | file. This list should normally start with the empty string. | |
217 | When @code{load} searches for a file it appends the suffixes in this | |
218 | list, in order, to the file name, before searching for another file. | |
219 | ||
220 | Enabling Auto Compression mode appends the suffixes in | |
221 | @code{jka-compr-load-suffixes} to this list and disabling Auto | |
222 | Compression mode removes them again. The standard value of | |
223 | @code{load-file-rep-suffixes} if Auto Compression mode is disabled is | |
224 | @code{("")}. Given that the standard value of | |
225 | @code{jka-compr-load-suffixes} is @code{(".gz")}, the standard value | |
226 | of @code{load-file-rep-suffixes} if Auto Compression mode is enabled | |
227 | is @code{("" ".gz")}. | |
228 | @end defvar | |
229 | ||
230 | @defun get-load-suffixes | |
231 | This function returns the list of all suffixes that @code{load} should | |
232 | try, in order, when its @var{must-suffix} argument is non-@code{nil}. | |
233 | This takes both @code{load-suffixes} and @code{load-file-rep-suffixes} | |
234 | into account. If @code{load-suffixes}, @code{jka-compr-load-suffixes} | |
235 | and @code{load-file-rep-suffixes} all have their standard values, this | |
236 | function returns @code{(".elc" ".elc.gz" ".el" ".el.gz")} if Auto | |
237 | Compression mode is enabled and @code{(".elc" ".el")} if Auto | |
238 | Compression mode is disabled. | |
239 | @end defun | |
240 | ||
241 | To summarize, @code{load} normally first tries the suffixes in the | |
242 | value of @code{(get-load-suffixes)} and then those in | |
243 | @code{load-file-rep-suffixes}. If @var{nosuffix} is non-@code{nil}, | |
244 | it skips the former group, and if @var{must-suffix} is non-@code{nil}, | |
245 | it skips the latter group. | |
246 | ||
247 | @node Library Search | |
248 | @section Library Search | |
249 | @cindex library search | |
250 | @cindex find library | |
251 | ||
252 | When Emacs loads a Lisp library, it searches for the library | |
253 | in a list of directories specified by the variable @code{load-path}. | |
254 | ||
6c1e4b46 | 255 | @defvar load-path |
8fc85b20 | 256 | @cindex @env{EMACSLOADPATH} environment variable |
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257 | The value of this variable is a list of directories to search when |
258 | loading files with @code{load}. Each element is a string (which must be | |
259 | a directory name) or @code{nil} (which stands for the current working | |
260 | directory). | |
6c1e4b46 | 261 | @end defvar |
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263 | Each time Emacs starts up, it sets up the value of @code{load-path} |
264 | in several steps. First, it initializes @code{load-path} to the | |
265 | directories specified by the environment variable @env{EMACSLOADPATH}, | |
266 | if that exists. The syntax of @env{EMACSLOADPATH} is the same as used | |
267 | for @code{PATH}; directory names are separated by @samp{:} (or | |
268 | @samp{;}, on some operating systems), and @samp{.} stands for the | |
269 | current default directory. Here is an example of how to set | |
270 | @env{EMACSLOADPATH} variable from @command{sh}: | |
b8d4c8d0 | 271 | |
ddff3351 | 272 | @example |
b8d4c8d0 | 273 | export EMACSLOADPATH |
6c1e4b46 | 274 | EMACSLOADPATH=/home/foo/.emacs.d/lisp:/opt/emacs/lisp |
ddff3351 | 275 | @end example |
b8d4c8d0 | 276 | |
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277 | @noindent |
278 | Here is how to set it from @code{csh}: | |
b8d4c8d0 | 279 | |
ddff3351 | 280 | @example |
6c1e4b46 | 281 | setenv EMACSLOADPATH /home/foo/.emacs.d/lisp:/opt/emacs/lisp |
ddff3351 | 282 | @end example |
b8d4c8d0 | 283 | |
ab4c47d3 | 284 | @cindex site-lisp directories |
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285 | If @env{EMACSLOADPATH} is not set (which is usually the case), Emacs |
286 | initializes @code{load-path} with the following two directories: | |
b8d4c8d0 | 287 | |
ddff3351 | 288 | @example |
b8d4c8d0 | 289 | "/usr/local/share/emacs/@var{version}/site-lisp" |
ddff3351 | 290 | @end example |
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291 | |
292 | @noindent | |
293 | and | |
294 | ||
ddff3351 | 295 | @example |
b8d4c8d0 | 296 | "/usr/local/share/emacs/site-lisp" |
ddff3351 | 297 | @end example |
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298 | |
299 | @noindent | |
300 | The first one is for locally installed packages for a particular Emacs | |
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301 | version; the second is for locally installed packages meant for use |
302 | with all installed Emacs versions. | |
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303 | |
304 | If you run Emacs from the directory where it was built---that is, an | |
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305 | executable that has not been formally installed---Emacs puts two more |
306 | directories in @code{load-path}. These are the @code{lisp} and | |
307 | @code{site-lisp} subdirectories of the main build directory. (Both | |
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308 | are represented as absolute file names.) |
309 | ||
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310 | Next, Emacs ``expands'' the initial list of directories in |
311 | @code{load-path} by adding the subdirectories of those directories. | |
312 | Both immediate subdirectories and subdirectories multiple levels down | |
313 | are added. But it excludes subdirectories whose names do not start | |
314 | with a letter or digit, and subdirectories named @file{RCS} or | |
315 | @file{CVS}, and subdirectories containing a file named | |
316 | @file{.nosearch}. | |
317 | ||
318 | Next, Emacs adds any extra load directory that you specify using the | |
319 | @samp{-L} command-line option (@pxref{Action Arguments,,,emacs, The | |
320 | GNU Emacs Manual}). It also adds the directories where optional | |
321 | packages are installed, if any (@pxref{Packaging Basics}). | |
322 | ||
323 | It is common to add code to one's init file (@pxref{Init File}) to | |
324 | add one or more directories to @code{load-path}. For example: | |
325 | ||
ddff3351 | 326 | @example |
6c1e4b46 | 327 | (push "~/.emacs.d/lisp" load-path) |
ddff3351 | 328 | @end example |
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329 | |
330 | Dumping Emacs uses a special value of @code{load-path}. If the | |
331 | value of @code{load-path} at the end of dumping is unchanged (that is, | |
332 | still the same special value), the dumped Emacs switches to the | |
333 | ordinary @code{load-path} value when it starts up, as described above. | |
334 | But if @code{load-path} has any other value at the end of dumping, | |
335 | that value is used for execution of the dumped Emacs also. | |
336 | ||
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337 | @deffn Command locate-library library &optional nosuffix path interactive-call |
338 | This command finds the precise file name for library @var{library}. It | |
339 | searches for the library in the same way @code{load} does, and the | |
340 | argument @var{nosuffix} has the same meaning as in @code{load}: don't | |
341 | add suffixes @samp{.elc} or @samp{.el} to the specified name | |
342 | @var{library}. | |
343 | ||
344 | If the @var{path} is non-@code{nil}, that list of directories is used | |
345 | instead of @code{load-path}. | |
346 | ||
347 | When @code{locate-library} is called from a program, it returns the file | |
348 | name as a string. When the user runs @code{locate-library} | |
349 | interactively, the argument @var{interactive-call} is @code{t}, and this | |
350 | tells @code{locate-library} to display the file name in the echo area. | |
351 | @end deffn | |
352 | ||
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353 | @cindex shadowed Lisp files |
354 | @deffn Command list-load-path-shadows &optional stringp | |
355 | This command shows a list of @dfn{shadowed} Emacs Lisp files. A | |
356 | shadowed file is one that will not normally be loaded, despite being | |
357 | in a directory on @code{load-path}, due to the existence of another | |
358 | similarly-named file in a directory earlier on @code{load-path}. | |
359 | ||
360 | For instance, suppose @code{load-path} is set to | |
361 | ||
ddff3351 | 362 | @example |
e6cf7a82 | 363 | ("/opt/emacs/site-lisp" "/usr/share/emacs/23.3/lisp") |
ddff3351 | 364 | @end example |
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365 | |
366 | @noindent | |
367 | and that both these directories contain a file named @file{foo.el}. | |
368 | Then @code{(require 'foo)} never loads the file in the second | |
369 | directory. Such a situation might indicate a problem in the way Emacs | |
370 | was installed. | |
371 | ||
372 | When called from Lisp, this function prints a message listing the | |
373 | shadowed files, instead of displaying them in a buffer. If the | |
374 | optional argument @code{stringp} is non-@code{nil}, it instead returns | |
375 | the shadowed files as a string. | |
376 | @end deffn | |
377 | ||
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378 | @node Loading Non-ASCII |
379 | @section Loading Non-@acronym{ASCII} Characters | |
380 | ||
381 | When Emacs Lisp programs contain string constants with non-@acronym{ASCII} | |
382 | characters, these can be represented within Emacs either as unibyte | |
383 | strings or as multibyte strings (@pxref{Text Representations}). Which | |
384 | representation is used depends on how the file is read into Emacs. If | |
385 | it is read with decoding into multibyte representation, the text of the | |
386 | Lisp program will be multibyte text, and its string constants will be | |
387 | multibyte strings. If a file containing Latin-1 characters (for | |
388 | example) is read without decoding, the text of the program will be | |
389 | unibyte text, and its string constants will be unibyte strings. | |
390 | @xref{Coding Systems}. | |
391 | ||
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392 | In most Emacs Lisp programs, the fact that non-@acronym{ASCII} |
393 | strings are multibyte strings should not be noticeable, since | |
394 | inserting them in unibyte buffers converts them to unibyte | |
395 | automatically. However, if this does make a difference, you can force | |
396 | a particular Lisp file to be interpreted as unibyte by writing | |
b8a82b69 | 397 | @samp{coding: raw-text} in a local variables section. With |
6c1e4b46 | 398 | that designator, the file will unconditionally be interpreted as |
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399 | unibyte. This can matter when making keybindings to |
400 | non-@acronym{ASCII} characters written as @code{?v@var{literal}}. | |
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401 | |
402 | @node Autoload | |
403 | @section Autoload | |
404 | @cindex autoload | |
405 | ||
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406 | The @dfn{autoload} facility lets you register the existence of a |
407 | function or macro, but put off loading the file that defines it. The | |
408 | first call to the function automatically loads the proper library, in | |
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409 | order to install the real definition and other associated code, then |
410 | runs the real definition as if it had been loaded all along. | |
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411 | Autoloading can also be triggered by looking up the documentation of |
412 | the function or macro (@pxref{Documentation Basics}). | |
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413 | |
414 | There are two ways to set up an autoloaded function: by calling | |
415 | @code{autoload}, and by writing a special ``magic'' comment in the | |
416 | source before the real definition. @code{autoload} is the low-level | |
417 | primitive for autoloading; any Lisp program can call @code{autoload} at | |
418 | any time. Magic comments are the most convenient way to make a function | |
419 | autoload, for packages installed along with Emacs. These comments do | |
420 | nothing on their own, but they serve as a guide for the command | |
421 | @code{update-file-autoloads}, which constructs calls to @code{autoload} | |
422 | and arranges to execute them when Emacs is built. | |
423 | ||
424 | @defun autoload function filename &optional docstring interactive type | |
425 | This function defines the function (or macro) named @var{function} so as | |
426 | to load automatically from @var{filename}. The string @var{filename} | |
427 | specifies the file to load to get the real definition of @var{function}. | |
428 | ||
429 | If @var{filename} does not contain either a directory name, or the | |
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430 | suffix @code{.el} or @code{.elc}, this function insists on adding one |
431 | of these suffixes, and it will not load from a file whose name is just | |
432 | @var{filename} with no added suffix. (The variable | |
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433 | @code{load-suffixes} specifies the exact required suffixes.) |
434 | ||
435 | The argument @var{docstring} is the documentation string for the | |
436 | function. Specifying the documentation string in the call to | |
437 | @code{autoload} makes it possible to look at the documentation without | |
438 | loading the function's real definition. Normally, this should be | |
439 | identical to the documentation string in the function definition | |
440 | itself. If it isn't, the function definition's documentation string | |
441 | takes effect when it is loaded. | |
442 | ||
443 | If @var{interactive} is non-@code{nil}, that says @var{function} can be | |
444 | called interactively. This lets completion in @kbd{M-x} work without | |
445 | loading @var{function}'s real definition. The complete interactive | |
446 | specification is not given here; it's not needed unless the user | |
447 | actually calls @var{function}, and when that happens, it's time to load | |
448 | the real definition. | |
449 | ||
450 | You can autoload macros and keymaps as well as ordinary functions. | |
451 | Specify @var{type} as @code{macro} if @var{function} is really a macro. | |
452 | Specify @var{type} as @code{keymap} if @var{function} is really a | |
453 | keymap. Various parts of Emacs need to know this information without | |
454 | loading the real definition. | |
455 | ||
456 | An autoloaded keymap loads automatically during key lookup when a prefix | |
457 | key's binding is the symbol @var{function}. Autoloading does not occur | |
458 | for other kinds of access to the keymap. In particular, it does not | |
459 | happen when a Lisp program gets the keymap from the value of a variable | |
460 | and calls @code{define-key}; not even if the variable name is the same | |
461 | symbol @var{function}. | |
462 | ||
463 | @cindex function cell in autoload | |
e29e39c9 CY |
464 | if @var{function} already has non-void function definition that is not |
465 | an autoload object, this function does nothing and returns @code{nil}. | |
466 | Otherwise, it constructs an autoload object (@pxref{Autoload Type}), | |
467 | and stores it as the function definition for @var{function}. The | |
468 | autoload object has this form: | |
b8d4c8d0 GM |
469 | |
470 | @example | |
471 | (autoload @var{filename} @var{docstring} @var{interactive} @var{type}) | |
472 | @end example | |
473 | ||
474 | For example, | |
475 | ||
476 | @example | |
477 | @group | |
478 | (symbol-function 'run-prolog) | |
479 | @result{} (autoload "prolog" 169681 t nil) | |
480 | @end group | |
481 | @end example | |
482 | ||
483 | @noindent | |
484 | In this case, @code{"prolog"} is the name of the file to load, 169681 | |
485 | refers to the documentation string in the | |
486 | @file{emacs/etc/DOC-@var{version}} file (@pxref{Documentation Basics}), | |
487 | @code{t} means the function is interactive, and @code{nil} that it is | |
488 | not a macro or a keymap. | |
489 | @end defun | |
490 | ||
e29e39c9 CY |
491 | @defun autoloadp object |
492 | This function returns non-@code{nil} if @var{object} is an autoload | |
493 | object. For example, to check if @code{run-prolog} is defined as an | |
494 | autoloaded function, evaluate | |
495 | ||
496 | @smallexample | |
497 | (autoloadp (symbol-function 'run-prolog)) | |
498 | @end smallexample | |
499 | @end defun | |
500 | ||
b8d4c8d0 GM |
501 | @cindex autoload errors |
502 | The autoloaded file usually contains other definitions and may require | |
503 | or provide one or more features. If the file is not completely loaded | |
504 | (due to an error in the evaluation of its contents), any function | |
505 | definitions or @code{provide} calls that occurred during the load are | |
506 | undone. This is to ensure that the next attempt to call any function | |
507 | autoloading from this file will try again to load the file. If not for | |
508 | this, then some of the functions in the file might be defined by the | |
509 | aborted load, but fail to work properly for the lack of certain | |
510 | subroutines not loaded successfully because they come later in the file. | |
511 | ||
512 | If the autoloaded file fails to define the desired Lisp function or | |
513 | macro, then an error is signaled with data @code{"Autoloading failed to | |
514 | define function @var{function-name}"}. | |
515 | ||
516 | @findex update-file-autoloads | |
517 | @findex update-directory-autoloads | |
518 | @cindex magic autoload comment | |
519 | @cindex autoload cookie | |
520 | @anchor{autoload cookie} | |
521 | A magic autoload comment (often called an @dfn{autoload cookie}) | |
522 | consists of @samp{;;;###autoload}, on a line by itself, | |
523 | just before the real definition of the function in its | |
524 | autoloadable source file. The command @kbd{M-x update-file-autoloads} | |
525 | writes a corresponding @code{autoload} call into @file{loaddefs.el}. | |
b8afe7e4 EZ |
526 | (The string that serves as the autoload cookie and the name of the |
527 | file generated by @code{update-file-autoloads} can be changed from the | |
528 | above defaults, see below.) | |
b8d4c8d0 GM |
529 | Building Emacs loads @file{loaddefs.el} and thus calls @code{autoload}. |
530 | @kbd{M-x update-directory-autoloads} is even more powerful; it updates | |
531 | autoloads for all files in the current directory. | |
532 | ||
533 | The same magic comment can copy any kind of form into | |
bc44be50 CY |
534 | @file{loaddefs.el}. The form following the magic comment is copied |
535 | verbatim, @emph{except} if it is one of the forms which the autoload | |
1df7defd | 536 | facility handles specially (e.g., by conversion into an |
bc44be50 CY |
537 | @code{autoload} call). The forms which are not copied verbatim are |
538 | the following: | |
539 | ||
540 | @table @asis | |
541 | @item Definitions for function or function-like objects: | |
0d8e94e9 GM |
542 | @code{defun} and @code{defmacro}; also @code{cl-defun} and |
543 | @code{cl-defmacro} (@pxref{Argument Lists,,,cl,Common Lisp Extensions}), | |
544 | and @code{define-overloadable-function} (see the commentary in | |
bc44be50 CY |
545 | @file{mode-local.el}). |
546 | ||
547 | @item Definitions for major or minor modes: | |
7eac3782 | 548 | @code{define-minor-mode}, @code{define-globalized-minor-mode}, |
84f4a531 CY |
549 | @code{define-generic-mode}, @code{define-derived-mode}, |
550 | @code{easy-mmode-define-minor-mode}, | |
7eac3782 | 551 | @code{easy-mmode-define-global-mode}, @code{define-compilation-mode}, |
84f4a531 | 552 | and @code{define-global-minor-mode}. |
bc44be50 CY |
553 | |
554 | @item Other definition types: | |
555 | @code{defcustom}, @code{defgroup}, @code{defclass} | |
556 | (@pxref{Top,EIEIO,,eieio,EIEIO}), and @code{define-skeleton} (see the | |
557 | commentary in @file{skeleton.el}). | |
558 | @end table | |
b8d4c8d0 GM |
559 | |
560 | You can also use a magic comment to execute a form at build time | |
561 | @emph{without} executing it when the file itself is loaded. To do this, | |
562 | write the form @emph{on the same line} as the magic comment. Since it | |
563 | is in a comment, it does nothing when you load the source file; but | |
564 | @kbd{M-x update-file-autoloads} copies it to @file{loaddefs.el}, where | |
565 | it is executed while building Emacs. | |
566 | ||
567 | The following example shows how @code{doctor} is prepared for | |
568 | autoloading with a magic comment: | |
569 | ||
ddff3351 | 570 | @example |
b8d4c8d0 GM |
571 | ;;;###autoload |
572 | (defun doctor () | |
573 | "Switch to *doctor* buffer and start giving psychotherapy." | |
574 | (interactive) | |
575 | (switch-to-buffer "*doctor*") | |
576 | (doctor-mode)) | |
ddff3351 | 577 | @end example |
b8d4c8d0 GM |
578 | |
579 | @noindent | |
580 | Here's what that produces in @file{loaddefs.el}: | |
581 | ||
ddff3351 | 582 | @example |
b8d4c8d0 GM |
583 | (autoload (quote doctor) "doctor" "\ |
584 | Switch to *doctor* buffer and start giving psychotherapy. | |
585 | ||
586 | \(fn)" t nil) | |
ddff3351 | 587 | @end example |
b8d4c8d0 GM |
588 | |
589 | @noindent | |
590 | @cindex @code{fn} in function's documentation string | |
591 | The backslash and newline immediately following the double-quote are a | |
592 | convention used only in the preloaded uncompiled Lisp files such as | |
593 | @file{loaddefs.el}; they tell @code{make-docfile} to put the | |
594 | documentation string in the @file{etc/DOC} file. @xref{Building Emacs}. | |
595 | See also the commentary in @file{lib-src/make-docfile.c}. @samp{(fn)} | |
596 | in the usage part of the documentation string is replaced with the | |
597 | function's name when the various help functions (@pxref{Help | |
598 | Functions}) display it. | |
599 | ||
600 | If you write a function definition with an unusual macro that is not | |
601 | one of the known and recognized function definition methods, use of an | |
602 | ordinary magic autoload comment would copy the whole definition into | |
603 | @code{loaddefs.el}. That is not desirable. You can put the desired | |
604 | @code{autoload} call into @code{loaddefs.el} instead by writing this: | |
605 | ||
ddff3351 | 606 | @example |
b8d4c8d0 GM |
607 | ;;;###autoload (autoload 'foo "myfile") |
608 | (mydefunmacro foo | |
609 | ...) | |
ddff3351 | 610 | @end example |
b8d4c8d0 | 611 | |
b8afe7e4 EZ |
612 | You can use a non-default string as the autoload cookie and have the |
613 | corresponding autoload calls written into a file whose name is | |
614 | different from the default @file{loaddefs.el}. Emacs provides two | |
615 | variables to control this: | |
616 | ||
617 | @defvar generate-autoload-cookie | |
618 | The value of this variable should be a string whose syntax is a Lisp | |
619 | comment. @kbd{M-x update-file-autoloads} copies the Lisp form that | |
620 | follows the cookie into the autoload file it generates. The default | |
621 | value of this variable is @code{";;;###autoload"}. | |
622 | @end defvar | |
623 | ||
624 | @defvar generated-autoload-file | |
625 | The value of this variable names an Emacs Lisp file where the autoload | |
626 | calls should go. The default value is @file{loaddefs.el}, but you can | |
627 | override that, e.g., in the ``Local Variables'' section of a | |
628 | @file{.el} file (@pxref{File Local Variables}). The autoload file is | |
629 | assumed to contain a trailer starting with a formfeed character. | |
630 | @end defvar | |
631 | ||
e29e39c9 CY |
632 | The following function may be used to explicitly load the library |
633 | specified by an autoload object: | |
634 | ||
635 | @defun autoload-do-load autoload &optional name macro-only | |
636 | This function performs the loading specified by @var{autoload}, which | |
5c6ce1c7 | 637 | should be an autoload object. The optional argument @var{name}, if |
e29e39c9 CY |
638 | non-@code{nil}, should be a symbol whose function value is |
639 | @var{autoload}; in that case, the return value of this function is the | |
640 | symbol's new function value. If the value of the optional argument | |
641 | @var{macro-only} is @code{macro}, this function avoids loading a | |
642 | function, only a macro. | |
643 | @end defun | |
644 | ||
b8d4c8d0 GM |
645 | @node Repeated Loading |
646 | @section Repeated Loading | |
647 | @cindex repeated loading | |
648 | ||
649 | You can load a given file more than once in an Emacs session. For | |
650 | example, after you have rewritten and reinstalled a function definition | |
651 | by editing it in a buffer, you may wish to return to the original | |
652 | version; you can do this by reloading the file it came from. | |
653 | ||
654 | When you load or reload files, bear in mind that the @code{load} and | |
655 | @code{load-library} functions automatically load a byte-compiled file | |
656 | rather than a non-compiled file of similar name. If you rewrite a file | |
657 | that you intend to save and reinstall, you need to byte-compile the new | |
658 | version; otherwise Emacs will load the older, byte-compiled file instead | |
659 | of your newer, non-compiled file! If that happens, the message | |
660 | displayed when loading the file includes, @samp{(compiled; note, source is | |
661 | newer)}, to remind you to recompile it. | |
662 | ||
663 | When writing the forms in a Lisp library file, keep in mind that the | |
664 | file might be loaded more than once. For example, think about whether | |
665 | each variable should be reinitialized when you reload the library; | |
666 | @code{defvar} does not change the value if the variable is already | |
667 | initialized. (@xref{Defining Variables}.) | |
668 | ||
669 | The simplest way to add an element to an alist is like this: | |
670 | ||
671 | @example | |
672 | (push '(leif-mode " Leif") minor-mode-alist) | |
673 | @end example | |
674 | ||
675 | @noindent | |
dc401175 CY |
676 | But this would add multiple elements if the library is reloaded. To |
677 | avoid the problem, use @code{add-to-list} (@pxref{List Variables}): | |
b8d4c8d0 GM |
678 | |
679 | @example | |
9af167bc | 680 | (add-to-list 'minor-mode-alist '(leif-mode " Leif")) |
b8d4c8d0 GM |
681 | @end example |
682 | ||
683 | Occasionally you will want to test explicitly whether a library has | |
dc401175 CY |
684 | already been loaded. If the library uses @code{provide} to provide a |
685 | named feature, you can use @code{featurep} earlier in the file to test | |
686 | whether the @code{provide} call has been executed before (@pxref{Named | |
687 | Features}). Alternatively, you could use something like this: | |
b8d4c8d0 GM |
688 | |
689 | @example | |
690 | (defvar foo-was-loaded nil) | |
691 | ||
692 | (unless foo-was-loaded | |
693 | @var{execute-first-time-only} | |
694 | (setq foo-was-loaded t)) | |
695 | @end example | |
696 | ||
697 | @noindent | |
b8d4c8d0 GM |
698 | |
699 | @node Named Features | |
700 | @section Features | |
701 | @cindex features | |
702 | @cindex requiring features | |
703 | @cindex providing features | |
704 | ||
705 | @code{provide} and @code{require} are an alternative to | |
706 | @code{autoload} for loading files automatically. They work in terms of | |
707 | named @dfn{features}. Autoloading is triggered by calling a specific | |
708 | function, but a feature is loaded the first time another program asks | |
709 | for it by name. | |
710 | ||
711 | A feature name is a symbol that stands for a collection of functions, | |
712 | variables, etc. The file that defines them should @dfn{provide} the | |
713 | feature. Another program that uses them may ensure they are defined by | |
714 | @dfn{requiring} the feature. This loads the file of definitions if it | |
715 | hasn't been loaded already. | |
716 | ||
dc401175 | 717 | @cindex load error with require |
b8d4c8d0 GM |
718 | To require the presence of a feature, call @code{require} with the |
719 | feature name as argument. @code{require} looks in the global variable | |
720 | @code{features} to see whether the desired feature has been provided | |
721 | already. If not, it loads the feature from the appropriate file. This | |
722 | file should call @code{provide} at the top level to add the feature to | |
723 | @code{features}; if it fails to do so, @code{require} signals an error. | |
b8d4c8d0 | 724 | |
14a1f380 GM |
725 | For example, in @file{idlwave.el}, the definition for |
726 | @code{idlwave-complete-filename} includes the following code: | |
b8d4c8d0 | 727 | |
ddff3351 | 728 | @example |
14a1f380 GM |
729 | (defun idlwave-complete-filename () |
730 | "Use the comint stuff to complete a file name." | |
731 | (require 'comint) | |
732 | (let* ((comint-file-name-chars "~/A-Za-z0-9+@:_.$#%=@{@}\\-") | |
733 | (comint-completion-addsuffix nil) | |
734 | ...) | |
735 | (comint-dynamic-complete-filename))) | |
ddff3351 | 736 | @end example |
b8d4c8d0 GM |
737 | |
738 | @noindent | |
739 | The expression @code{(require 'comint)} loads the file @file{comint.el} | |
14a1f380 GM |
740 | if it has not yet been loaded, ensuring that |
741 | @code{comint-dynamic-complete-filename} is defined. Features are | |
742 | normally named after the files that provide them, so that | |
743 | @code{require} need not be given the file name. (Note that it is | |
744 | important that the @code{require} statement be outside the body of the | |
745 | @code{let}. Loading a library while its variables are let-bound can | |
746 | have unintended consequences, namely the variables becoming unbound | |
747 | after the let exits.) | |
b8d4c8d0 GM |
748 | |
749 | The @file{comint.el} file contains the following top-level expression: | |
750 | ||
ddff3351 | 751 | @example |
b8d4c8d0 | 752 | (provide 'comint) |
ddff3351 | 753 | @end example |
b8d4c8d0 GM |
754 | |
755 | @noindent | |
756 | This adds @code{comint} to the global @code{features} list, so that | |
757 | @code{(require 'comint)} will henceforth know that nothing needs to be | |
758 | done. | |
759 | ||
760 | @cindex byte-compiling @code{require} | |
761 | When @code{require} is used at top level in a file, it takes effect | |
762 | when you byte-compile that file (@pxref{Byte Compilation}) as well as | |
763 | when you load it. This is in case the required package contains macros | |
5c63cc6b | 764 | that the byte compiler must know about. It also avoids byte compiler |
b8d4c8d0 GM |
765 | warnings for functions and variables defined in the file loaded with |
766 | @code{require}. | |
767 | ||
768 | Although top-level calls to @code{require} are evaluated during | |
769 | byte compilation, @code{provide} calls are not. Therefore, you can | |
770 | ensure that a file of definitions is loaded before it is byte-compiled | |
771 | by including a @code{provide} followed by a @code{require} for the same | |
772 | feature, as in the following example. | |
773 | ||
ddff3351 | 774 | @example |
b8d4c8d0 GM |
775 | @group |
776 | (provide 'my-feature) ; @r{Ignored by byte compiler,} | |
777 | ; @r{evaluated by @code{load}.} | |
778 | (require 'my-feature) ; @r{Evaluated by byte compiler.} | |
779 | @end group | |
ddff3351 | 780 | @end example |
b8d4c8d0 GM |
781 | |
782 | @noindent | |
783 | The compiler ignores the @code{provide}, then processes the | |
784 | @code{require} by loading the file in question. Loading the file does | |
785 | execute the @code{provide} call, so the subsequent @code{require} call | |
786 | does nothing when the file is loaded. | |
787 | ||
788 | @defun provide feature &optional subfeatures | |
789 | This function announces that @var{feature} is now loaded, or being | |
790 | loaded, into the current Emacs session. This means that the facilities | |
791 | associated with @var{feature} are or will be available for other Lisp | |
792 | programs. | |
793 | ||
4c98b9ed GM |
794 | The direct effect of calling @code{provide} is if not already in |
795 | @var{features} then to add @var{feature} to the front of that list and | |
796 | call any @code{eval-after-load} code waiting for it (@pxref{Hooks for | |
797 | Loading}). The argument @var{feature} must be a symbol. | |
798 | @code{provide} returns @var{feature}. | |
b8d4c8d0 GM |
799 | |
800 | If provided, @var{subfeatures} should be a list of symbols indicating | |
801 | a set of specific subfeatures provided by this version of | |
802 | @var{feature}. You can test the presence of a subfeature using | |
803 | @code{featurep}. The idea of subfeatures is that you use them when a | |
804 | package (which is one @var{feature}) is complex enough to make it | |
805 | useful to give names to various parts or functionalities of the | |
806 | package, which might or might not be loaded, or might or might not be | |
807 | present in a given version. @xref{Network Feature Testing}, for | |
808 | an example. | |
809 | ||
ddff3351 | 810 | @example |
b8d4c8d0 GM |
811 | features |
812 | @result{} (bar bish) | |
813 | ||
814 | (provide 'foo) | |
815 | @result{} foo | |
816 | features | |
817 | @result{} (foo bar bish) | |
ddff3351 | 818 | @end example |
b8d4c8d0 GM |
819 | |
820 | When a file is loaded to satisfy an autoload, and it stops due to an | |
821 | error in the evaluation of its contents, any function definitions or | |
822 | @code{provide} calls that occurred during the load are undone. | |
823 | @xref{Autoload}. | |
824 | @end defun | |
825 | ||
826 | @defun require feature &optional filename noerror | |
827 | This function checks whether @var{feature} is present in the current | |
828 | Emacs session (using @code{(featurep @var{feature})}; see below). The | |
829 | argument @var{feature} must be a symbol. | |
830 | ||
831 | If the feature is not present, then @code{require} loads @var{filename} | |
832 | with @code{load}. If @var{filename} is not supplied, then the name of | |
833 | the symbol @var{feature} is used as the base file name to load. | |
834 | However, in this case, @code{require} insists on finding @var{feature} | |
835 | with an added @samp{.el} or @samp{.elc} suffix (possibly extended with | |
836 | a compression suffix); a file whose name is just @var{feature} won't | |
837 | be used. (The variable @code{load-suffixes} specifies the exact | |
838 | required Lisp suffixes.) | |
839 | ||
840 | If @var{noerror} is non-@code{nil}, that suppresses errors from actual | |
841 | loading of the file. In that case, @code{require} returns @code{nil} | |
842 | if loading the file fails. Normally, @code{require} returns | |
843 | @var{feature}. | |
844 | ||
845 | If loading the file succeeds but does not provide @var{feature}, | |
846 | @code{require} signals an error, @samp{Required feature @var{feature} | |
847 | was not provided}. | |
848 | @end defun | |
849 | ||
850 | @defun featurep feature &optional subfeature | |
851 | This function returns @code{t} if @var{feature} has been provided in | |
1df7defd | 852 | the current Emacs session (i.e., if @var{feature} is a member of |
b8d4c8d0 GM |
853 | @code{features}.) If @var{subfeature} is non-@code{nil}, then the |
854 | function returns @code{t} only if that subfeature is provided as well | |
1df7defd | 855 | (i.e., if @var{subfeature} is a member of the @code{subfeature} |
b8d4c8d0 GM |
856 | property of the @var{feature} symbol.) |
857 | @end defun | |
858 | ||
859 | @defvar features | |
860 | The value of this variable is a list of symbols that are the features | |
861 | loaded in the current Emacs session. Each symbol was put in this list | |
862 | with a call to @code{provide}. The order of the elements in the | |
863 | @code{features} list is not significant. | |
864 | @end defvar | |
865 | ||
866 | @node Where Defined | |
867 | @section Which File Defined a Certain Symbol | |
868 | ||
869 | @defun symbol-file symbol &optional type | |
870 | This function returns the name of the file that defined @var{symbol}. | |
d632fb82 MR |
871 | If @var{type} is @code{nil}, then any kind of definition is acceptable. |
872 | If @var{type} is @code{defun}, @code{defvar}, or @code{defface}, that | |
873 | specifies function definition, variable definition, or face definition | |
874 | only. | |
875 | ||
876 | The value is normally an absolute file name. It can also be @code{nil}, | |
877 | if the definition is not associated with any file. If @var{symbol} | |
878 | specifies an autoloaded function, the value can be a relative file name | |
879 | without extension. | |
b8d4c8d0 GM |
880 | @end defun |
881 | ||
882 | The basis for @code{symbol-file} is the data in the variable | |
883 | @code{load-history}. | |
884 | ||
885 | @defvar load-history | |
da0bbbc4 | 886 | The value of this variable is an alist that associates the names of |
4801c5fa CY |
887 | loaded library files with the names of the functions and variables |
888 | they defined, as well as the features they provided or required. | |
889 | ||
890 | Each element in this alist describes one loaded library (including | |
891 | libraries that are preloaded at startup). It is a list whose @sc{car} | |
892 | is the absolute file name of the library (a string). The rest of the | |
893 | list elements have these forms: | |
b8d4c8d0 GM |
894 | |
895 | @table @code | |
896 | @item @var{var} | |
897 | The symbol @var{var} was defined as a variable. | |
898 | @item (defun . @var{fun}) | |
899 | The function @var{fun} was defined. | |
900 | @item (t . @var{fun}) | |
901 | The function @var{fun} was previously an autoload before this library | |
902 | redefined it as a function. The following element is always | |
903 | @code{(defun . @var{fun})}, which represents defining @var{fun} as a | |
904 | function. | |
905 | @item (autoload . @var{fun}) | |
906 | The function @var{fun} was defined as an autoload. | |
6a57054b JB |
907 | @item (defface . @var{face}) |
908 | The face @var{face} was defined. | |
b8d4c8d0 GM |
909 | @item (require . @var{feature}) |
910 | The feature @var{feature} was required. | |
911 | @item (provide . @var{feature}) | |
912 | The feature @var{feature} was provided. | |
913 | @end table | |
914 | ||
915 | The value of @code{load-history} may have one element whose @sc{car} is | |
916 | @code{nil}. This element describes definitions made with | |
917 | @code{eval-buffer} on a buffer that is not visiting a file. | |
918 | @end defvar | |
919 | ||
920 | The command @code{eval-region} updates @code{load-history}, but does so | |
921 | by adding the symbols defined to the element for the file being visited, | |
922 | rather than replacing that element. @xref{Eval}. | |
923 | ||
924 | @node Unloading | |
925 | @section Unloading | |
926 | @cindex unloading packages | |
927 | ||
928 | @c Emacs 19 feature | |
929 | You can discard the functions and variables loaded by a library to | |
930 | reclaim memory for other Lisp objects. To do this, use the function | |
931 | @code{unload-feature}: | |
932 | ||
933 | @deffn Command unload-feature feature &optional force | |
934 | This command unloads the library that provided feature @var{feature}. | |
935 | It undefines all functions, macros, and variables defined in that | |
936 | library with @code{defun}, @code{defalias}, @code{defsubst}, | |
937 | @code{defmacro}, @code{defconst}, @code{defvar}, and @code{defcustom}. | |
938 | It then restores any autoloads formerly associated with those symbols. | |
939 | (Loading saves these in the @code{autoload} property of the symbol.) | |
940 | ||
b8d4c8d0 GM |
941 | Before restoring the previous definitions, @code{unload-feature} runs |
942 | @code{remove-hook} to remove functions in the library from certain | |
d1069532 SM |
943 | hooks. These hooks include variables whose names end in @samp{-hook} |
944 | (or the deprecated suffix @samp{-hooks}), plus those listed in | |
0ade8edb RS |
945 | @code{unload-feature-special-hooks}, as well as |
946 | @code{auto-mode-alist}. This is to prevent Emacs from ceasing to | |
947 | function because important hooks refer to functions that are no longer | |
948 | defined. | |
b8d4c8d0 | 949 | |
0ade8edb RS |
950 | Standard unloading activities also undoes ELP profiling of functions |
951 | in that library, unprovides any features provided by the library, and | |
952 | cancels timers held in variables defined by the library. | |
953 | ||
954 | @vindex @var{feature}-unload-function | |
b8d4c8d0 | 955 | If these measures are not sufficient to prevent malfunction, a library |
0ade8edb RS |
956 | can define an explicit unloader named @code{@var{feature}-unload-function}. |
957 | If that symbol is defined as a function, @code{unload-feature} calls | |
958 | it with no arguments before doing anything else. It can do whatever | |
959 | is appropriate to unload the library. If it returns @code{nil}, | |
960 | @code{unload-feature} proceeds to take the normal unload actions. | |
961 | Otherwise it considers the job to be done. | |
b8d4c8d0 GM |
962 | |
963 | Ordinarily, @code{unload-feature} refuses to unload a library on which | |
964 | other loaded libraries depend. (A library @var{a} depends on library | |
965 | @var{b} if @var{a} contains a @code{require} for @var{b}.) If the | |
966 | optional argument @var{force} is non-@code{nil}, dependencies are | |
967 | ignored and you can unload any library. | |
968 | @end deffn | |
969 | ||
970 | The @code{unload-feature} function is written in Lisp; its actions are | |
971 | based on the variable @code{load-history}. | |
972 | ||
973 | @defvar unload-feature-special-hooks | |
974 | This variable holds a list of hooks to be scanned before unloading a | |
975 | library, to remove functions defined in the library. | |
976 | @end defvar | |
977 | ||
978 | @node Hooks for Loading | |
979 | @section Hooks for Loading | |
980 | @cindex loading hooks | |
981 | @cindex hooks for loading | |
982 | ||
c3863713 CY |
983 | You can ask for code to be executed each time Emacs loads a library, |
984 | by using the variable @code{after-load-functions}: | |
985 | ||
986 | @defvar after-load-functions | |
987 | This abnormal hook is run after loading a file. Each function in the | |
988 | hook is called with a single argument, the absolute filename of the | |
989 | file that was just loaded. | |
990 | @end defvar | |
991 | ||
992 | If you want code to be executed when a @emph{particular} library is | |
993 | loaded, use the function @code{eval-after-load}: | |
b8d4c8d0 GM |
994 | |
995 | @defun eval-after-load library form | |
996 | This function arranges to evaluate @var{form} at the end of loading | |
997 | the file @var{library}, each time @var{library} is loaded. If | |
998 | @var{library} is already loaded, it evaluates @var{form} right away. | |
999 | Don't forget to quote @var{form}! | |
1000 | ||
1001 | You don't need to give a directory or extension in the file name | |
c3863713 | 1002 | @var{library}. Normally, you just give a bare file name, like this: |
b8d4c8d0 GM |
1003 | |
1004 | @example | |
1005 | (eval-after-load "edebug" '(def-edebug-spec c-point t)) | |
1006 | @end example | |
1007 | ||
1008 | To restrict which files can trigger the evaluation, include a | |
1009 | directory or an extension or both in @var{library}. Only a file whose | |
1010 | absolute true name (i.e., the name with all symbolic links chased out) | |
1011 | matches all the given name components will match. In the following | |
1012 | example, @file{my_inst.elc} or @file{my_inst.elc.gz} in some directory | |
1013 | @code{..../foo/bar} will trigger the evaluation, but not | |
1014 | @file{my_inst.el}: | |
1015 | ||
1016 | @example | |
1017 | (eval-after-load "foo/bar/my_inst.elc" @dots{}) | |
1018 | @end example | |
1019 | ||
1df7defd | 1020 | @var{library} can also be a feature (i.e., a symbol), in which case |
3fa173b4 SM |
1021 | @var{form} is evaluated at the end of any file where |
1022 | @code{(provide @var{library})} is called. | |
b8d4c8d0 GM |
1023 | |
1024 | An error in @var{form} does not undo the load, but does prevent | |
1025 | execution of the rest of @var{form}. | |
1026 | @end defun | |
1027 | ||
c3863713 CY |
1028 | Normally, well-designed Lisp programs should not use |
1029 | @code{eval-after-load}. If you need to examine and set the variables | |
1030 | defined in another library (those meant for outside use), you can do | |
1031 | it immediately---there is no need to wait until the library is loaded. | |
1032 | If you need to call functions defined by that library, you should load | |
1033 | the library, preferably with @code{require} (@pxref{Named Features}). | |
b8d4c8d0 | 1034 | |
b8d4c8d0 | 1035 | @defvar after-load-alist |
c3863713 CY |
1036 | This variable stores an alist built by @code{eval-after-load}, |
1037 | containing the expressions to evaluate when certain libraries are | |
1038 | loaded. Each element looks like this: | |
b8d4c8d0 GM |
1039 | |
1040 | @example | |
1041 | (@var{regexp-or-feature} @var{forms}@dots{}) | |
1042 | @end example | |
1043 | ||
1044 | The key @var{regexp-or-feature} is either a regular expression or a | |
c3863713 CY |
1045 | symbol, and the value is a list of forms. The forms are evaluated |
1046 | when the key matches the absolute true name or feature name of the | |
1047 | library being loaded. | |
b8d4c8d0 | 1048 | @end defvar |