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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2001, | |
6ed161e1 | 4 | @c 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc. |
b8d4c8d0 | 5 | @c See the file elisp.texi for copying conditions. |
6336d8c3 | 6 | @setfilename ../../info/loading |
b8d4c8d0 GM |
7 | @node Loading, Byte Compilation, Customization, Top |
8 | @chapter Loading | |
9 | @cindex loading | |
10 | @cindex library | |
11 | @cindex Lisp library | |
12 | ||
13 | Loading a file of Lisp code means bringing its contents into the Lisp | |
14 | environment in the form of Lisp objects. Emacs finds and opens the | |
15 | file, reads the text, evaluates each form, and then closes the file. | |
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 | ||
32 | A file containing Lisp code is often called a @dfn{library}. Thus, | |
33 | the ``Rmail library'' is a file containing code for Rmail mode. | |
34 | Similarly, a ``Lisp library directory'' is a directory of files | |
35 | containing Lisp code. | |
36 | ||
37 | @menu | |
38 | * How Programs Do Loading:: The @code{load} function and others. | |
39 | * Load Suffixes:: Details about the suffixes that @code{load} tries. | |
40 | * Library Search:: Finding a library to load. | |
41 | * Loading Non-ASCII:: Non-@acronym{ASCII} characters in Emacs Lisp files. | |
42 | * Autoload:: Setting up a function to autoload. | |
43 | * Repeated Loading:: Precautions about loading a file twice. | |
44 | * Named Features:: Loading a library if it isn't already loaded. | |
45 | * Where Defined:: Finding which file defined a certain symbol. | |
46 | * Unloading:: How to "unload" a library that was loaded. | |
47 | * Hooks for Loading:: Providing code to be run when | |
48 | particular libraries are loaded. | |
49 | @end menu | |
50 | ||
51 | @node How Programs Do Loading | |
52 | @section How Programs Do Loading | |
53 | ||
54 | Emacs Lisp has several interfaces for loading. For example, | |
55 | @code{autoload} creates a placeholder object for a function defined in a | |
56 | file; trying to call the autoloading function loads the file to get the | |
57 | function's real definition (@pxref{Autoload}). @code{require} loads a | |
58 | file if it isn't already loaded (@pxref{Named Features}). Ultimately, | |
59 | all these facilities call the @code{load} function to do the work. | |
60 | ||
61 | @defun load filename &optional missing-ok nomessage nosuffix must-suffix | |
62 | This function finds and opens a file of Lisp code, evaluates all the | |
63 | forms in it, and closes the file. | |
64 | ||
65 | To find the file, @code{load} first looks for a file named | |
66 | @file{@var{filename}.elc}, that is, for a file whose name is | |
67 | @var{filename} with the extension @samp{.elc} appended. If such a | |
68 | file exists, it is loaded. If there is no file by that name, then | |
69 | @code{load} looks for a file named @file{@var{filename}.el}. If that | |
70 | file exists, it is loaded. Finally, if neither of those names is | |
71 | found, @code{load} looks for a file named @var{filename} with nothing | |
72 | appended, and loads it if it exists. (The @code{load} function is not | |
73 | clever about looking at @var{filename}. In the perverse case of a | |
74 | file named @file{foo.el.el}, evaluation of @code{(load "foo.el")} will | |
75 | indeed find it.) | |
76 | ||
77 | If Auto Compression mode is enabled, as it is by default, then if | |
78 | @code{load} can not find a file, it searches for a compressed version | |
79 | of the file before trying other file names. It decompresses and loads | |
80 | it if it exists. It looks for compressed versions by appending each | |
81 | of the suffixes in @code{jka-compr-load-suffixes} to the file name. | |
82 | The value of this variable must be a list of strings. Its standard | |
83 | value is @code{(".gz")}. | |
84 | ||
85 | If the optional argument @var{nosuffix} is non-@code{nil}, then | |
86 | @code{load} does not try the suffixes @samp{.elc} and @samp{.el}. In | |
87 | this case, you must specify the precise file name you want, except | |
88 | that, if Auto Compression mode is enabled, @code{load} will still use | |
89 | @code{jka-compr-load-suffixes} to find compressed versions. By | |
90 | specifying the precise file name and using @code{t} for | |
91 | @var{nosuffix}, you can prevent perverse file names such as | |
92 | @file{foo.el.el} from being tried. | |
93 | ||
94 | If the optional argument @var{must-suffix} is non-@code{nil}, then | |
95 | @code{load} insists that the file name used must end in either | |
96 | @samp{.el} or @samp{.elc} (possibly extended with a compression | |
97 | suffix), unless it contains an explicit directory name. | |
98 | ||
99 | If @var{filename} is a relative file name, such as @file{foo} or | |
100 | @file{baz/foo.bar}, @code{load} searches for the file using the variable | |
101 | @code{load-path}. It appends @var{filename} to each of the directories | |
102 | listed in @code{load-path}, and loads the first file it finds whose name | |
103 | matches. The current default directory is tried only if it is specified | |
104 | in @code{load-path}, where @code{nil} stands for the default directory. | |
105 | @code{load} tries all three possible suffixes in the first directory in | |
106 | @code{load-path}, then all three suffixes in the second directory, and | |
107 | so on. @xref{Library Search}. | |
108 | ||
109 | If you get a warning that @file{foo.elc} is older than @file{foo.el}, it | |
110 | means you should consider recompiling @file{foo.el}. @xref{Byte | |
111 | Compilation}. | |
112 | ||
113 | When loading a source file (not compiled), @code{load} performs | |
114 | character set translation just as Emacs would do when visiting the file. | |
115 | @xref{Coding Systems}. | |
116 | ||
117 | Messages like @samp{Loading foo...} and @samp{Loading foo...done} appear | |
118 | in the echo area during loading unless @var{nomessage} is | |
119 | non-@code{nil}. | |
120 | ||
121 | @cindex load errors | |
122 | Any unhandled errors while loading a file terminate loading. If the | |
123 | load was done for the sake of @code{autoload}, any function definitions | |
124 | made during the loading are undone. | |
125 | ||
126 | @kindex file-error | |
127 | If @code{load} can't find the file to load, then normally it signals the | |
128 | error @code{file-error} (with @samp{Cannot open load file | |
129 | @var{filename}}). But if @var{missing-ok} is non-@code{nil}, then | |
130 | @code{load} just returns @code{nil}. | |
131 | ||
132 | You can use the variable @code{load-read-function} to specify a function | |
133 | for @code{load} to use instead of @code{read} for reading expressions. | |
134 | See below. | |
135 | ||
136 | @code{load} returns @code{t} if the file loads successfully. | |
137 | @end defun | |
138 | ||
139 | @deffn Command load-file filename | |
140 | This command loads the file @var{filename}. If @var{filename} is a | |
141 | relative file name, then the current default directory is assumed. | |
142 | This command does not use @code{load-path}, and does not append | |
143 | suffixes. However, it does look for compressed versions (if Auto | |
144 | Compression Mode is enabled). Use this command if you wish to specify | |
145 | precisely the file name to load. | |
146 | @end deffn | |
147 | ||
148 | @deffn Command load-library library | |
149 | This command loads the library named @var{library}. It is equivalent to | |
f6de8a37 CY |
150 | @code{load}, except for the way it reads its argument interactively. |
151 | @xref{Lisp Libraries,,,emacs, The GNU Emacs Manual}. | |
b8d4c8d0 GM |
152 | @end deffn |
153 | ||
154 | @defvar load-in-progress | |
155 | This variable is non-@code{nil} if Emacs is in the process of loading a | |
156 | file, and it is @code{nil} otherwise. | |
157 | @end defvar | |
158 | ||
159 | @defvar load-read-function | |
160 | @anchor{Definition of load-read-function} | |
161 | @c do not allow page break at anchor; work around Texinfo deficiency. | |
162 | This variable specifies an alternate expression-reading function for | |
163 | @code{load} and @code{eval-region} to use instead of @code{read}. | |
164 | The function should accept one argument, just as @code{read} does. | |
165 | ||
166 | Normally, the variable's value is @code{nil}, which means those | |
167 | functions should use @code{read}. | |
168 | ||
169 | Instead of using this variable, it is cleaner to use another, newer | |
170 | feature: to pass the function as the @var{read-function} argument to | |
171 | @code{eval-region}. @xref{Definition of eval-region,, Eval}. | |
172 | @end defvar | |
173 | ||
174 | For information about how @code{load} is used in building Emacs, see | |
175 | @ref{Building Emacs}. | |
176 | ||
177 | @node Load Suffixes | |
178 | @section Load Suffixes | |
179 | We now describe some technical details about the exact suffixes that | |
180 | @code{load} tries. | |
181 | ||
182 | @defvar load-suffixes | |
183 | This is a list of suffixes indicating (compiled or source) Emacs Lisp | |
184 | files. It should not include the empty string. @code{load} uses | |
185 | these suffixes in order when it appends Lisp suffixes to the specified | |
186 | file name. The standard value is @code{(".elc" ".el")} which produces | |
187 | the behavior described in the previous section. | |
188 | @end defvar | |
189 | ||
190 | @defvar load-file-rep-suffixes | |
191 | This is a list of suffixes that indicate representations of the same | |
192 | file. This list should normally start with the empty string. | |
193 | When @code{load} searches for a file it appends the suffixes in this | |
194 | list, in order, to the file name, before searching for another file. | |
195 | ||
196 | Enabling Auto Compression mode appends the suffixes in | |
197 | @code{jka-compr-load-suffixes} to this list and disabling Auto | |
198 | Compression mode removes them again. The standard value of | |
199 | @code{load-file-rep-suffixes} if Auto Compression mode is disabled is | |
200 | @code{("")}. Given that the standard value of | |
201 | @code{jka-compr-load-suffixes} is @code{(".gz")}, the standard value | |
202 | of @code{load-file-rep-suffixes} if Auto Compression mode is enabled | |
203 | is @code{("" ".gz")}. | |
204 | @end defvar | |
205 | ||
206 | @defun get-load-suffixes | |
207 | This function returns the list of all suffixes that @code{load} should | |
208 | try, in order, when its @var{must-suffix} argument is non-@code{nil}. | |
209 | This takes both @code{load-suffixes} and @code{load-file-rep-suffixes} | |
210 | into account. If @code{load-suffixes}, @code{jka-compr-load-suffixes} | |
211 | and @code{load-file-rep-suffixes} all have their standard values, this | |
212 | function returns @code{(".elc" ".elc.gz" ".el" ".el.gz")} if Auto | |
213 | Compression mode is enabled and @code{(".elc" ".el")} if Auto | |
214 | Compression mode is disabled. | |
215 | @end defun | |
216 | ||
217 | To summarize, @code{load} normally first tries the suffixes in the | |
218 | value of @code{(get-load-suffixes)} and then those in | |
219 | @code{load-file-rep-suffixes}. If @var{nosuffix} is non-@code{nil}, | |
220 | it skips the former group, and if @var{must-suffix} is non-@code{nil}, | |
221 | it skips the latter group. | |
222 | ||
223 | @node Library Search | |
224 | @section Library Search | |
225 | @cindex library search | |
226 | @cindex find library | |
227 | ||
228 | When Emacs loads a Lisp library, it searches for the library | |
229 | in a list of directories specified by the variable @code{load-path}. | |
230 | ||
231 | @defopt load-path | |
232 | @cindex @code{EMACSLOADPATH} environment variable | |
233 | The value of this variable is a list of directories to search when | |
234 | loading files with @code{load}. Each element is a string (which must be | |
235 | a directory name) or @code{nil} (which stands for the current working | |
236 | directory). | |
237 | @end defopt | |
238 | ||
239 | The value of @code{load-path} is initialized from the environment | |
240 | variable @code{EMACSLOADPATH}, if that exists; otherwise its default | |
241 | value is specified in @file{emacs/src/epaths.h} when Emacs is built. | |
242 | Then the list is expanded by adding subdirectories of the directories | |
243 | in the list. | |
244 | ||
245 | The syntax of @code{EMACSLOADPATH} is the same as used for @code{PATH}; | |
246 | @samp{:} (or @samp{;}, according to the operating system) separates | |
247 | directory names, and @samp{.} is used for the current default directory. | |
248 | Here is an example of how to set your @code{EMACSLOADPATH} variable from | |
249 | a @code{csh} @file{.login} file: | |
250 | ||
251 | @smallexample | |
252 | setenv EMACSLOADPATH .:/user/bil/emacs:/usr/local/share/emacs/20.3/lisp | |
253 | @end smallexample | |
254 | ||
255 | Here is how to set it using @code{sh}: | |
256 | ||
257 | @smallexample | |
258 | export EMACSLOADPATH | |
259 | EMACSLOADPATH=.:/user/bil/emacs:/usr/local/share/emacs/20.3/lisp | |
260 | @end smallexample | |
261 | ||
262 | Here is an example of code you can place in your init file (@pxref{Init | |
263 | File}) to add several directories to the front of your default | |
264 | @code{load-path}: | |
265 | ||
266 | @smallexample | |
267 | @group | |
268 | (setq load-path | |
269 | (append (list nil "/user/bil/emacs" | |
270 | "/usr/local/lisplib" | |
271 | "~/emacs") | |
272 | load-path)) | |
273 | @end group | |
274 | @end smallexample | |
275 | ||
276 | @c Wordy to rid us of an overfull hbox. --rjc 15mar92 | |
277 | @noindent | |
278 | In this example, the path searches the current working directory first, | |
279 | followed then by the @file{/user/bil/emacs} directory, the | |
280 | @file{/usr/local/lisplib} directory, and the @file{~/emacs} directory, | |
281 | which are then followed by the standard directories for Lisp code. | |
282 | ||
283 | Dumping Emacs uses a special value of @code{load-path}. If the value of | |
284 | @code{load-path} at the end of dumping is unchanged (that is, still the | |
285 | same special value), the dumped Emacs switches to the ordinary | |
286 | @code{load-path} value when it starts up, as described above. But if | |
287 | @code{load-path} has any other value at the end of dumping, that value | |
288 | is used for execution of the dumped Emacs also. | |
289 | ||
290 | Therefore, if you want to change @code{load-path} temporarily for | |
291 | loading a few libraries in @file{site-init.el} or @file{site-load.el}, | |
292 | you should bind @code{load-path} locally with @code{let} around the | |
293 | calls to @code{load}. | |
294 | ||
295 | The default value of @code{load-path}, when running an Emacs which has | |
296 | been installed on the system, includes two special directories (and | |
297 | their subdirectories as well): | |
298 | ||
299 | @smallexample | |
300 | "/usr/local/share/emacs/@var{version}/site-lisp" | |
301 | @end smallexample | |
302 | ||
303 | @noindent | |
304 | and | |
305 | ||
306 | @smallexample | |
307 | "/usr/local/share/emacs/site-lisp" | |
308 | @end smallexample | |
309 | ||
310 | @noindent | |
311 | The first one is for locally installed packages for a particular Emacs | |
312 | version; the second is for locally installed packages meant for use with | |
313 | all installed Emacs versions. | |
314 | ||
315 | There are several reasons why a Lisp package that works well in one | |
316 | Emacs version can cause trouble in another. Sometimes packages need | |
317 | updating for incompatible changes in Emacs; sometimes they depend on | |
318 | undocumented internal Emacs data that can change without notice; | |
319 | sometimes a newer Emacs version incorporates a version of the package, | |
320 | and should be used only with that version. | |
321 | ||
322 | Emacs finds these directories' subdirectories and adds them to | |
323 | @code{load-path} when it starts up. Both immediate subdirectories and | |
324 | subdirectories multiple levels down are added to @code{load-path}. | |
325 | ||
326 | Not all subdirectories are included, though. Subdirectories whose | |
327 | names do not start with a letter or digit are excluded. Subdirectories | |
328 | named @file{RCS} or @file{CVS} are excluded. Also, a subdirectory which | |
329 | contains a file named @file{.nosearch} is excluded. You can use these | |
330 | methods to prevent certain subdirectories of the @file{site-lisp} | |
331 | directories from being searched. | |
332 | ||
333 | If you run Emacs from the directory where it was built---that is, an | |
334 | executable that has not been formally installed---then @code{load-path} | |
335 | normally contains two additional directories. These are the @code{lisp} | |
336 | and @code{site-lisp} subdirectories of the main build directory. (Both | |
337 | are represented as absolute file names.) | |
338 | ||
339 | @deffn Command locate-library library &optional nosuffix path interactive-call | |
340 | This command finds the precise file name for library @var{library}. It | |
341 | searches for the library in the same way @code{load} does, and the | |
342 | argument @var{nosuffix} has the same meaning as in @code{load}: don't | |
343 | add suffixes @samp{.elc} or @samp{.el} to the specified name | |
344 | @var{library}. | |
345 | ||
346 | If the @var{path} is non-@code{nil}, that list of directories is used | |
347 | instead of @code{load-path}. | |
348 | ||
349 | When @code{locate-library} is called from a program, it returns the file | |
350 | name as a string. When the user runs @code{locate-library} | |
351 | interactively, the argument @var{interactive-call} is @code{t}, and this | |
352 | tells @code{locate-library} to display the file name in the echo area. | |
353 | @end deffn | |
354 | ||
355 | @node Loading Non-ASCII | |
356 | @section Loading Non-@acronym{ASCII} Characters | |
357 | ||
358 | When Emacs Lisp programs contain string constants with non-@acronym{ASCII} | |
359 | characters, these can be represented within Emacs either as unibyte | |
360 | strings or as multibyte strings (@pxref{Text Representations}). Which | |
361 | representation is used depends on how the file is read into Emacs. If | |
362 | it is read with decoding into multibyte representation, the text of the | |
363 | Lisp program will be multibyte text, and its string constants will be | |
364 | multibyte strings. If a file containing Latin-1 characters (for | |
365 | example) is read without decoding, the text of the program will be | |
366 | unibyte text, and its string constants will be unibyte strings. | |
367 | @xref{Coding Systems}. | |
368 | ||
369 | To make the results more predictable, Emacs always performs decoding | |
370 | into the multibyte representation when loading Lisp files, even if it | |
371 | was started with the @samp{--unibyte} option. This means that string | |
372 | constants with non-@acronym{ASCII} characters translate into multibyte | |
373 | strings. The only exception is when a particular file specifies no | |
374 | decoding. | |
375 | ||
376 | The reason Emacs is designed this way is so that Lisp programs give | |
377 | predictable results, regardless of how Emacs was started. In addition, | |
378 | this enables programs that depend on using multibyte text to work even | |
4e3b4528 | 379 | in a unibyte Emacs. |
b8d4c8d0 GM |
380 | |
381 | In most Emacs Lisp programs, the fact that non-@acronym{ASCII} strings are | |
382 | multibyte strings should not be noticeable, since inserting them in | |
383 | unibyte buffers converts them to unibyte automatically. However, if | |
384 | this does make a difference, you can force a particular Lisp file to be | |
385 | interpreted as unibyte by writing @samp{-*-unibyte: t;-*-} in a | |
386 | comment on the file's first line. With that designator, the file will | |
387 | unconditionally be interpreted as unibyte, even in an ordinary | |
388 | multibyte Emacs session. This can matter when making keybindings to | |
389 | non-@acronym{ASCII} characters written as @code{?v@var{literal}}. | |
390 | ||
391 | @node Autoload | |
392 | @section Autoload | |
393 | @cindex autoload | |
394 | ||
395 | The @dfn{autoload} facility allows you to make a function or macro | |
396 | known in Lisp, but put off loading the file that defines it. The first | |
397 | call to the function automatically reads the proper file to install the | |
398 | real definition and other associated code, then runs the real definition | |
399 | as if it had been loaded all along. | |
400 | ||
401 | There are two ways to set up an autoloaded function: by calling | |
402 | @code{autoload}, and by writing a special ``magic'' comment in the | |
403 | source before the real definition. @code{autoload} is the low-level | |
404 | primitive for autoloading; any Lisp program can call @code{autoload} at | |
405 | any time. Magic comments are the most convenient way to make a function | |
406 | autoload, for packages installed along with Emacs. These comments do | |
407 | nothing on their own, but they serve as a guide for the command | |
408 | @code{update-file-autoloads}, which constructs calls to @code{autoload} | |
409 | and arranges to execute them when Emacs is built. | |
410 | ||
411 | @defun autoload function filename &optional docstring interactive type | |
412 | This function defines the function (or macro) named @var{function} so as | |
413 | to load automatically from @var{filename}. The string @var{filename} | |
414 | specifies the file to load to get the real definition of @var{function}. | |
415 | ||
416 | If @var{filename} does not contain either a directory name, or the | |
417 | suffix @code{.el} or @code{.elc}, then @code{autoload} insists on adding | |
418 | one of these suffixes, and it will not load from a file whose name is | |
419 | just @var{filename} with no added suffix. (The variable | |
420 | @code{load-suffixes} specifies the exact required suffixes.) | |
421 | ||
422 | The argument @var{docstring} is the documentation string for the | |
423 | function. Specifying the documentation string in the call to | |
424 | @code{autoload} makes it possible to look at the documentation without | |
425 | loading the function's real definition. Normally, this should be | |
426 | identical to the documentation string in the function definition | |
427 | itself. If it isn't, the function definition's documentation string | |
428 | takes effect when it is loaded. | |
429 | ||
430 | If @var{interactive} is non-@code{nil}, that says @var{function} can be | |
431 | called interactively. This lets completion in @kbd{M-x} work without | |
432 | loading @var{function}'s real definition. The complete interactive | |
433 | specification is not given here; it's not needed unless the user | |
434 | actually calls @var{function}, and when that happens, it's time to load | |
435 | the real definition. | |
436 | ||
437 | You can autoload macros and keymaps as well as ordinary functions. | |
438 | Specify @var{type} as @code{macro} if @var{function} is really a macro. | |
439 | Specify @var{type} as @code{keymap} if @var{function} is really a | |
440 | keymap. Various parts of Emacs need to know this information without | |
441 | loading the real definition. | |
442 | ||
443 | An autoloaded keymap loads automatically during key lookup when a prefix | |
444 | key's binding is the symbol @var{function}. Autoloading does not occur | |
445 | for other kinds of access to the keymap. In particular, it does not | |
446 | happen when a Lisp program gets the keymap from the value of a variable | |
447 | and calls @code{define-key}; not even if the variable name is the same | |
448 | symbol @var{function}. | |
449 | ||
450 | @cindex function cell in autoload | |
451 | If @var{function} already has a non-void function definition that is not | |
452 | an autoload object, @code{autoload} does nothing and returns @code{nil}. | |
453 | If the function cell of @var{function} is void, or is already an autoload | |
454 | object, then it is defined as an autoload object like this: | |
455 | ||
456 | @example | |
457 | (autoload @var{filename} @var{docstring} @var{interactive} @var{type}) | |
458 | @end example | |
459 | ||
460 | For example, | |
461 | ||
462 | @example | |
463 | @group | |
464 | (symbol-function 'run-prolog) | |
465 | @result{} (autoload "prolog" 169681 t nil) | |
466 | @end group | |
467 | @end example | |
468 | ||
469 | @noindent | |
470 | In this case, @code{"prolog"} is the name of the file to load, 169681 | |
471 | refers to the documentation string in the | |
472 | @file{emacs/etc/DOC-@var{version}} file (@pxref{Documentation Basics}), | |
473 | @code{t} means the function is interactive, and @code{nil} that it is | |
474 | not a macro or a keymap. | |
475 | @end defun | |
476 | ||
477 | @cindex autoload errors | |
478 | The autoloaded file usually contains other definitions and may require | |
479 | or provide one or more features. If the file is not completely loaded | |
480 | (due to an error in the evaluation of its contents), any function | |
481 | definitions or @code{provide} calls that occurred during the load are | |
482 | undone. This is to ensure that the next attempt to call any function | |
483 | autoloading from this file will try again to load the file. If not for | |
484 | this, then some of the functions in the file might be defined by the | |
485 | aborted load, but fail to work properly for the lack of certain | |
486 | subroutines not loaded successfully because they come later in the file. | |
487 | ||
488 | If the autoloaded file fails to define the desired Lisp function or | |
489 | macro, then an error is signaled with data @code{"Autoloading failed to | |
490 | define function @var{function-name}"}. | |
491 | ||
492 | @findex update-file-autoloads | |
493 | @findex update-directory-autoloads | |
494 | @cindex magic autoload comment | |
495 | @cindex autoload cookie | |
496 | @anchor{autoload cookie} | |
497 | A magic autoload comment (often called an @dfn{autoload cookie}) | |
498 | consists of @samp{;;;###autoload}, on a line by itself, | |
499 | just before the real definition of the function in its | |
500 | autoloadable source file. The command @kbd{M-x update-file-autoloads} | |
501 | writes a corresponding @code{autoload} call into @file{loaddefs.el}. | |
b8afe7e4 EZ |
502 | (The string that serves as the autoload cookie and the name of the |
503 | file generated by @code{update-file-autoloads} can be changed from the | |
504 | above defaults, see below.) | |
b8d4c8d0 GM |
505 | Building Emacs loads @file{loaddefs.el} and thus calls @code{autoload}. |
506 | @kbd{M-x update-directory-autoloads} is even more powerful; it updates | |
507 | autoloads for all files in the current directory. | |
508 | ||
509 | The same magic comment can copy any kind of form into | |
510 | @file{loaddefs.el}. If the form following the magic comment is not a | |
511 | function-defining form or a @code{defcustom} form, it is copied | |
512 | verbatim. ``Function-defining forms'' include @code{define-skeleton}, | |
513 | @code{define-derived-mode}, @code{define-generic-mode} and | |
514 | @code{define-minor-mode} as well as @code{defun} and | |
515 | @code{defmacro}. To save space, a @code{defcustom} form is converted to | |
516 | a @code{defvar} in @file{loaddefs.el}, with some additional information | |
517 | if it uses @code{:require}. | |
518 | ||
519 | You can also use a magic comment to execute a form at build time | |
520 | @emph{without} executing it when the file itself is loaded. To do this, | |
521 | write the form @emph{on the same line} as the magic comment. Since it | |
522 | is in a comment, it does nothing when you load the source file; but | |
523 | @kbd{M-x update-file-autoloads} copies it to @file{loaddefs.el}, where | |
524 | it is executed while building Emacs. | |
525 | ||
526 | The following example shows how @code{doctor} is prepared for | |
527 | autoloading with a magic comment: | |
528 | ||
529 | @smallexample | |
530 | ;;;###autoload | |
531 | (defun doctor () | |
532 | "Switch to *doctor* buffer and start giving psychotherapy." | |
533 | (interactive) | |
534 | (switch-to-buffer "*doctor*") | |
535 | (doctor-mode)) | |
536 | @end smallexample | |
537 | ||
538 | @noindent | |
539 | Here's what that produces in @file{loaddefs.el}: | |
540 | ||
541 | @smallexample | |
542 | (autoload (quote doctor) "doctor" "\ | |
543 | Switch to *doctor* buffer and start giving psychotherapy. | |
544 | ||
545 | \(fn)" t nil) | |
546 | @end smallexample | |
547 | ||
548 | @noindent | |
549 | @cindex @code{fn} in function's documentation string | |
550 | The backslash and newline immediately following the double-quote are a | |
551 | convention used only in the preloaded uncompiled Lisp files such as | |
552 | @file{loaddefs.el}; they tell @code{make-docfile} to put the | |
553 | documentation string in the @file{etc/DOC} file. @xref{Building Emacs}. | |
554 | See also the commentary in @file{lib-src/make-docfile.c}. @samp{(fn)} | |
555 | in the usage part of the documentation string is replaced with the | |
556 | function's name when the various help functions (@pxref{Help | |
557 | Functions}) display it. | |
558 | ||
559 | If you write a function definition with an unusual macro that is not | |
560 | one of the known and recognized function definition methods, use of an | |
561 | ordinary magic autoload comment would copy the whole definition into | |
562 | @code{loaddefs.el}. That is not desirable. You can put the desired | |
563 | @code{autoload} call into @code{loaddefs.el} instead by writing this: | |
564 | ||
565 | @smallexample | |
566 | ;;;###autoload (autoload 'foo "myfile") | |
567 | (mydefunmacro foo | |
568 | ...) | |
569 | @end smallexample | |
570 | ||
b8afe7e4 EZ |
571 | You can use a non-default string as the autoload cookie and have the |
572 | corresponding autoload calls written into a file whose name is | |
573 | different from the default @file{loaddefs.el}. Emacs provides two | |
574 | variables to control this: | |
575 | ||
576 | @defvar generate-autoload-cookie | |
577 | The value of this variable should be a string whose syntax is a Lisp | |
578 | comment. @kbd{M-x update-file-autoloads} copies the Lisp form that | |
579 | follows the cookie into the autoload file it generates. The default | |
580 | value of this variable is @code{";;;###autoload"}. | |
581 | @end defvar | |
582 | ||
583 | @defvar generated-autoload-file | |
584 | The value of this variable names an Emacs Lisp file where the autoload | |
585 | calls should go. The default value is @file{loaddefs.el}, but you can | |
586 | override that, e.g., in the ``Local Variables'' section of a | |
587 | @file{.el} file (@pxref{File Local Variables}). The autoload file is | |
588 | assumed to contain a trailer starting with a formfeed character. | |
589 | @end defvar | |
590 | ||
b8d4c8d0 GM |
591 | @node Repeated Loading |
592 | @section Repeated Loading | |
593 | @cindex repeated loading | |
594 | ||
595 | You can load a given file more than once in an Emacs session. For | |
596 | example, after you have rewritten and reinstalled a function definition | |
597 | by editing it in a buffer, you may wish to return to the original | |
598 | version; you can do this by reloading the file it came from. | |
599 | ||
600 | When you load or reload files, bear in mind that the @code{load} and | |
601 | @code{load-library} functions automatically load a byte-compiled file | |
602 | rather than a non-compiled file of similar name. If you rewrite a file | |
603 | that you intend to save and reinstall, you need to byte-compile the new | |
604 | version; otherwise Emacs will load the older, byte-compiled file instead | |
605 | of your newer, non-compiled file! If that happens, the message | |
606 | displayed when loading the file includes, @samp{(compiled; note, source is | |
607 | newer)}, to remind you to recompile it. | |
608 | ||
609 | When writing the forms in a Lisp library file, keep in mind that the | |
610 | file might be loaded more than once. For example, think about whether | |
611 | each variable should be reinitialized when you reload the library; | |
612 | @code{defvar} does not change the value if the variable is already | |
613 | initialized. (@xref{Defining Variables}.) | |
614 | ||
615 | The simplest way to add an element to an alist is like this: | |
616 | ||
617 | @example | |
618 | (push '(leif-mode " Leif") minor-mode-alist) | |
619 | @end example | |
620 | ||
621 | @noindent | |
dc401175 CY |
622 | But this would add multiple elements if the library is reloaded. To |
623 | avoid the problem, use @code{add-to-list} (@pxref{List Variables}): | |
b8d4c8d0 GM |
624 | |
625 | @example | |
9af167bc | 626 | (add-to-list 'minor-mode-alist '(leif-mode " Leif")) |
b8d4c8d0 GM |
627 | @end example |
628 | ||
629 | Occasionally you will want to test explicitly whether a library has | |
dc401175 CY |
630 | already been loaded. If the library uses @code{provide} to provide a |
631 | named feature, you can use @code{featurep} earlier in the file to test | |
632 | whether the @code{provide} call has been executed before (@pxref{Named | |
633 | Features}). Alternatively, you could use something like this: | |
b8d4c8d0 GM |
634 | |
635 | @example | |
636 | (defvar foo-was-loaded nil) | |
637 | ||
638 | (unless foo-was-loaded | |
639 | @var{execute-first-time-only} | |
640 | (setq foo-was-loaded t)) | |
641 | @end example | |
642 | ||
643 | @noindent | |
b8d4c8d0 GM |
644 | |
645 | @node Named Features | |
646 | @section Features | |
647 | @cindex features | |
648 | @cindex requiring features | |
649 | @cindex providing features | |
650 | ||
651 | @code{provide} and @code{require} are an alternative to | |
652 | @code{autoload} for loading files automatically. They work in terms of | |
653 | named @dfn{features}. Autoloading is triggered by calling a specific | |
654 | function, but a feature is loaded the first time another program asks | |
655 | for it by name. | |
656 | ||
657 | A feature name is a symbol that stands for a collection of functions, | |
658 | variables, etc. The file that defines them should @dfn{provide} the | |
659 | feature. Another program that uses them may ensure they are defined by | |
660 | @dfn{requiring} the feature. This loads the file of definitions if it | |
661 | hasn't been loaded already. | |
662 | ||
dc401175 | 663 | @cindex load error with require |
b8d4c8d0 GM |
664 | To require the presence of a feature, call @code{require} with the |
665 | feature name as argument. @code{require} looks in the global variable | |
666 | @code{features} to see whether the desired feature has been provided | |
667 | already. If not, it loads the feature from the appropriate file. This | |
668 | file should call @code{provide} at the top level to add the feature to | |
669 | @code{features}; if it fails to do so, @code{require} signals an error. | |
b8d4c8d0 GM |
670 | |
671 | For example, in @file{emacs/lisp/prolog.el}, | |
672 | the definition for @code{run-prolog} includes the following code: | |
673 | ||
674 | @smallexample | |
675 | (defun run-prolog () | |
676 | "Run an inferior Prolog process, with I/O via buffer *prolog*." | |
677 | (interactive) | |
678 | (require 'comint) | |
679 | (switch-to-buffer (make-comint "prolog" prolog-program-name)) | |
680 | (inferior-prolog-mode)) | |
681 | @end smallexample | |
682 | ||
683 | @noindent | |
684 | The expression @code{(require 'comint)} loads the file @file{comint.el} | |
685 | if it has not yet been loaded. This ensures that @code{make-comint} is | |
686 | defined. Features are normally named after the files that provide them, | |
687 | so that @code{require} need not be given the file name. | |
688 | ||
689 | The @file{comint.el} file contains the following top-level expression: | |
690 | ||
691 | @smallexample | |
692 | (provide 'comint) | |
693 | @end smallexample | |
694 | ||
695 | @noindent | |
696 | This adds @code{comint} to the global @code{features} list, so that | |
697 | @code{(require 'comint)} will henceforth know that nothing needs to be | |
698 | done. | |
699 | ||
700 | @cindex byte-compiling @code{require} | |
701 | When @code{require} is used at top level in a file, it takes effect | |
702 | when you byte-compile that file (@pxref{Byte Compilation}) as well as | |
703 | when you load it. This is in case the required package contains macros | |
5c63cc6b | 704 | that the byte compiler must know about. It also avoids byte compiler |
b8d4c8d0 GM |
705 | warnings for functions and variables defined in the file loaded with |
706 | @code{require}. | |
707 | ||
708 | Although top-level calls to @code{require} are evaluated during | |
709 | byte compilation, @code{provide} calls are not. Therefore, you can | |
710 | ensure that a file of definitions is loaded before it is byte-compiled | |
711 | by including a @code{provide} followed by a @code{require} for the same | |
712 | feature, as in the following example. | |
713 | ||
714 | @smallexample | |
715 | @group | |
716 | (provide 'my-feature) ; @r{Ignored by byte compiler,} | |
717 | ; @r{evaluated by @code{load}.} | |
718 | (require 'my-feature) ; @r{Evaluated by byte compiler.} | |
719 | @end group | |
720 | @end smallexample | |
721 | ||
722 | @noindent | |
723 | The compiler ignores the @code{provide}, then processes the | |
724 | @code{require} by loading the file in question. Loading the file does | |
725 | execute the @code{provide} call, so the subsequent @code{require} call | |
726 | does nothing when the file is loaded. | |
727 | ||
728 | @defun provide feature &optional subfeatures | |
729 | This function announces that @var{feature} is now loaded, or being | |
730 | loaded, into the current Emacs session. This means that the facilities | |
731 | associated with @var{feature} are or will be available for other Lisp | |
732 | programs. | |
733 | ||
4c98b9ed GM |
734 | The direct effect of calling @code{provide} is if not already in |
735 | @var{features} then to add @var{feature} to the front of that list and | |
736 | call any @code{eval-after-load} code waiting for it (@pxref{Hooks for | |
737 | Loading}). The argument @var{feature} must be a symbol. | |
738 | @code{provide} returns @var{feature}. | |
b8d4c8d0 GM |
739 | |
740 | If provided, @var{subfeatures} should be a list of symbols indicating | |
741 | a set of specific subfeatures provided by this version of | |
742 | @var{feature}. You can test the presence of a subfeature using | |
743 | @code{featurep}. The idea of subfeatures is that you use them when a | |
744 | package (which is one @var{feature}) is complex enough to make it | |
745 | useful to give names to various parts or functionalities of the | |
746 | package, which might or might not be loaded, or might or might not be | |
747 | present in a given version. @xref{Network Feature Testing}, for | |
748 | an example. | |
749 | ||
750 | @smallexample | |
751 | features | |
752 | @result{} (bar bish) | |
753 | ||
754 | (provide 'foo) | |
755 | @result{} foo | |
756 | features | |
757 | @result{} (foo bar bish) | |
758 | @end smallexample | |
759 | ||
760 | When a file is loaded to satisfy an autoload, and it stops due to an | |
761 | error in the evaluation of its contents, any function definitions or | |
762 | @code{provide} calls that occurred during the load are undone. | |
763 | @xref{Autoload}. | |
764 | @end defun | |
765 | ||
766 | @defun require feature &optional filename noerror | |
767 | This function checks whether @var{feature} is present in the current | |
768 | Emacs session (using @code{(featurep @var{feature})}; see below). The | |
769 | argument @var{feature} must be a symbol. | |
770 | ||
771 | If the feature is not present, then @code{require} loads @var{filename} | |
772 | with @code{load}. If @var{filename} is not supplied, then the name of | |
773 | the symbol @var{feature} is used as the base file name to load. | |
774 | However, in this case, @code{require} insists on finding @var{feature} | |
775 | with an added @samp{.el} or @samp{.elc} suffix (possibly extended with | |
776 | a compression suffix); a file whose name is just @var{feature} won't | |
777 | be used. (The variable @code{load-suffixes} specifies the exact | |
778 | required Lisp suffixes.) | |
779 | ||
780 | If @var{noerror} is non-@code{nil}, that suppresses errors from actual | |
781 | loading of the file. In that case, @code{require} returns @code{nil} | |
782 | if loading the file fails. Normally, @code{require} returns | |
783 | @var{feature}. | |
784 | ||
785 | If loading the file succeeds but does not provide @var{feature}, | |
786 | @code{require} signals an error, @samp{Required feature @var{feature} | |
787 | was not provided}. | |
788 | @end defun | |
789 | ||
790 | @defun featurep feature &optional subfeature | |
791 | This function returns @code{t} if @var{feature} has been provided in | |
792 | the current Emacs session (i.e.@:, if @var{feature} is a member of | |
793 | @code{features}.) If @var{subfeature} is non-@code{nil}, then the | |
794 | function returns @code{t} only if that subfeature is provided as well | |
795 | (i.e.@: if @var{subfeature} is a member of the @code{subfeature} | |
796 | property of the @var{feature} symbol.) | |
797 | @end defun | |
798 | ||
799 | @defvar features | |
800 | The value of this variable is a list of symbols that are the features | |
801 | loaded in the current Emacs session. Each symbol was put in this list | |
802 | with a call to @code{provide}. The order of the elements in the | |
803 | @code{features} list is not significant. | |
804 | @end defvar | |
805 | ||
806 | @node Where Defined | |
807 | @section Which File Defined a Certain Symbol | |
808 | ||
809 | @defun symbol-file symbol &optional type | |
810 | This function returns the name of the file that defined @var{symbol}. | |
d632fb82 MR |
811 | If @var{type} is @code{nil}, then any kind of definition is acceptable. |
812 | If @var{type} is @code{defun}, @code{defvar}, or @code{defface}, that | |
813 | specifies function definition, variable definition, or face definition | |
814 | only. | |
815 | ||
816 | The value is normally an absolute file name. It can also be @code{nil}, | |
817 | if the definition is not associated with any file. If @var{symbol} | |
818 | specifies an autoloaded function, the value can be a relative file name | |
819 | without extension. | |
b8d4c8d0 GM |
820 | @end defun |
821 | ||
822 | The basis for @code{symbol-file} is the data in the variable | |
823 | @code{load-history}. | |
824 | ||
825 | @defvar load-history | |
826 | This variable's value is an alist connecting library file names with the | |
827 | names of functions and variables they define, the features they provide, | |
828 | and the features they require. | |
829 | ||
830 | Each element is a list and describes one library. The @sc{car} of the | |
831 | list is the absolute file name of the library, as a string. The rest | |
832 | of the list elements have these forms: | |
833 | ||
834 | @table @code | |
835 | @item @var{var} | |
836 | The symbol @var{var} was defined as a variable. | |
837 | @item (defun . @var{fun}) | |
838 | The function @var{fun} was defined. | |
839 | @item (t . @var{fun}) | |
840 | The function @var{fun} was previously an autoload before this library | |
841 | redefined it as a function. The following element is always | |
842 | @code{(defun . @var{fun})}, which represents defining @var{fun} as a | |
843 | function. | |
844 | @item (autoload . @var{fun}) | |
845 | The function @var{fun} was defined as an autoload. | |
6a57054b JB |
846 | @item (defface . @var{face}) |
847 | The face @var{face} was defined. | |
b8d4c8d0 GM |
848 | @item (require . @var{feature}) |
849 | The feature @var{feature} was required. | |
850 | @item (provide . @var{feature}) | |
851 | The feature @var{feature} was provided. | |
852 | @end table | |
853 | ||
854 | The value of @code{load-history} may have one element whose @sc{car} is | |
855 | @code{nil}. This element describes definitions made with | |
856 | @code{eval-buffer} on a buffer that is not visiting a file. | |
857 | @end defvar | |
858 | ||
859 | The command @code{eval-region} updates @code{load-history}, but does so | |
860 | by adding the symbols defined to the element for the file being visited, | |
861 | rather than replacing that element. @xref{Eval}. | |
862 | ||
863 | @node Unloading | |
864 | @section Unloading | |
865 | @cindex unloading packages | |
866 | ||
867 | @c Emacs 19 feature | |
868 | You can discard the functions and variables loaded by a library to | |
869 | reclaim memory for other Lisp objects. To do this, use the function | |
870 | @code{unload-feature}: | |
871 | ||
872 | @deffn Command unload-feature feature &optional force | |
873 | This command unloads the library that provided feature @var{feature}. | |
874 | It undefines all functions, macros, and variables defined in that | |
875 | library with @code{defun}, @code{defalias}, @code{defsubst}, | |
876 | @code{defmacro}, @code{defconst}, @code{defvar}, and @code{defcustom}. | |
877 | It then restores any autoloads formerly associated with those symbols. | |
878 | (Loading saves these in the @code{autoload} property of the symbol.) | |
879 | ||
b8d4c8d0 GM |
880 | Before restoring the previous definitions, @code{unload-feature} runs |
881 | @code{remove-hook} to remove functions in the library from certain | |
882 | hooks. These hooks include variables whose names end in @samp{hook} | |
883 | or @samp{-hooks}, plus those listed in | |
0ade8edb RS |
884 | @code{unload-feature-special-hooks}, as well as |
885 | @code{auto-mode-alist}. This is to prevent Emacs from ceasing to | |
886 | function because important hooks refer to functions that are no longer | |
887 | defined. | |
b8d4c8d0 | 888 | |
0ade8edb RS |
889 | Standard unloading activities also undoes ELP profiling of functions |
890 | in that library, unprovides any features provided by the library, and | |
891 | cancels timers held in variables defined by the library. | |
892 | ||
893 | @vindex @var{feature}-unload-function | |
b8d4c8d0 | 894 | If these measures are not sufficient to prevent malfunction, a library |
0ade8edb RS |
895 | can define an explicit unloader named @code{@var{feature}-unload-function}. |
896 | If that symbol is defined as a function, @code{unload-feature} calls | |
897 | it with no arguments before doing anything else. It can do whatever | |
898 | is appropriate to unload the library. If it returns @code{nil}, | |
899 | @code{unload-feature} proceeds to take the normal unload actions. | |
900 | Otherwise it considers the job to be done. | |
b8d4c8d0 GM |
901 | |
902 | Ordinarily, @code{unload-feature} refuses to unload a library on which | |
903 | other loaded libraries depend. (A library @var{a} depends on library | |
904 | @var{b} if @var{a} contains a @code{require} for @var{b}.) If the | |
905 | optional argument @var{force} is non-@code{nil}, dependencies are | |
906 | ignored and you can unload any library. | |
907 | @end deffn | |
908 | ||
909 | The @code{unload-feature} function is written in Lisp; its actions are | |
910 | based on the variable @code{load-history}. | |
911 | ||
912 | @defvar unload-feature-special-hooks | |
913 | This variable holds a list of hooks to be scanned before unloading a | |
914 | library, to remove functions defined in the library. | |
915 | @end defvar | |
916 | ||
917 | @node Hooks for Loading | |
918 | @section Hooks for Loading | |
919 | @cindex loading hooks | |
920 | @cindex hooks for loading | |
921 | ||
922 | You can ask for code to be executed if and when a particular library is | |
923 | loaded, by calling @code{eval-after-load}. | |
924 | ||
925 | @defun eval-after-load library form | |
926 | This function arranges to evaluate @var{form} at the end of loading | |
927 | the file @var{library}, each time @var{library} is loaded. If | |
928 | @var{library} is already loaded, it evaluates @var{form} right away. | |
929 | Don't forget to quote @var{form}! | |
930 | ||
931 | You don't need to give a directory or extension in the file name | |
932 | @var{library}---normally you just give a bare file name, like this: | |
933 | ||
934 | @example | |
935 | (eval-after-load "edebug" '(def-edebug-spec c-point t)) | |
936 | @end example | |
937 | ||
938 | To restrict which files can trigger the evaluation, include a | |
939 | directory or an extension or both in @var{library}. Only a file whose | |
940 | absolute true name (i.e., the name with all symbolic links chased out) | |
941 | matches all the given name components will match. In the following | |
942 | example, @file{my_inst.elc} or @file{my_inst.elc.gz} in some directory | |
943 | @code{..../foo/bar} will trigger the evaluation, but not | |
944 | @file{my_inst.el}: | |
945 | ||
946 | @example | |
947 | (eval-after-load "foo/bar/my_inst.elc" @dots{}) | |
948 | @end example | |
949 | ||
950 | @var{library} can also be a feature (i.e.@: a symbol), in which case | |
951 | @var{form} is evaluated when @code{(provide @var{library})} is called. | |
952 | ||
953 | An error in @var{form} does not undo the load, but does prevent | |
954 | execution of the rest of @var{form}. | |
955 | @end defun | |
956 | ||
957 | In general, well-designed Lisp programs should not use this feature. | |
958 | The clean and modular ways to interact with a Lisp library are (1) | |
959 | examine and set the library's variables (those which are meant for | |
960 | outside use), and (2) call the library's functions. If you wish to | |
961 | do (1), you can do it immediately---there is no need to wait for when | |
962 | the library is loaded. To do (2), you must load the library (preferably | |
963 | with @code{require}). | |
964 | ||
965 | But it is OK to use @code{eval-after-load} in your personal | |
966 | customizations if you don't feel they must meet the design standards for | |
967 | programs meant for wider use. | |
968 | ||
969 | @defvar after-load-alist | |
970 | This variable, an alist built by @code{eval-after-load}, holds the | |
971 | expressions to evaluate when particular libraries are loaded. Each | |
972 | element looks like this: | |
973 | ||
974 | @example | |
975 | (@var{regexp-or-feature} @var{forms}@dots{}) | |
976 | @end example | |
977 | ||
978 | The key @var{regexp-or-feature} is either a regular expression or a | |
979 | symbol, and the value is a list of forms. The forms are evaluated when | |
980 | the key matches the absolute true name of the file being | |
981 | @code{load}ed or the symbol being @code{provide}d. | |
982 | @end defvar | |
983 | ||
984 | @ignore | |
985 | arch-tag: df731f89-0900-4389-a436-9105241b6f7a | |
986 | @end ignore |