| 1 | @c -*-texinfo-*- |
| 2 | @c This is part of the GNU Emacs Lisp Reference Manual. |
| 3 | @c Copyright (C) 1990-1995, 1998-1999, 2001-2012 |
| 4 | @c Free Software Foundation, Inc. |
| 5 | @c See the file elisp.texi for copying conditions. |
| 6 | @setfilename ../../info/loading |
| 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 |
| 14 | Lisp environment in the form of Lisp objects. Emacs finds and opens |
| 15 | the file, reads the text, evaluates each form, and then closes the |
| 16 | file. Such a file is also called a @dfn{Lisp library}. |
| 17 | |
| 18 | The load functions evaluate all the expressions in a file just |
| 19 | as the @code{eval-buffer} function evaluates all the |
| 20 | expressions in a buffer. The difference is that the load functions |
| 21 | read and evaluate the text in the file as found on disk, not the text |
| 22 | in an Emacs buffer. |
| 23 | |
| 24 | @cindex top-level form |
| 25 | The loaded file must contain Lisp expressions, either as source code |
| 26 | or as byte-compiled code. Each form in the file is called a |
| 27 | @dfn{top-level form}. There is no special format for the forms in a |
| 28 | loadable file; any form in a file may equally well be typed directly |
| 29 | into a buffer and evaluated there. (Indeed, most code is tested this |
| 30 | way.) Most often, the forms are function definitions and variable |
| 31 | definitions. |
| 32 | |
| 33 | @menu |
| 34 | * How Programs Do Loading:: The @code{load} function and others. |
| 35 | * Load Suffixes:: Details about the suffixes that @code{load} tries. |
| 36 | * Library Search:: Finding a library to load. |
| 37 | * Loading Non-ASCII:: Non-@acronym{ASCII} characters in Emacs Lisp files. |
| 38 | * Autoload:: Setting up a function to autoload. |
| 39 | * Repeated Loading:: Precautions about loading a file twice. |
| 40 | * Named Features:: Loading a library if it isn't already loaded. |
| 41 | * Where Defined:: Finding which file defined a certain symbol. |
| 42 | * Unloading:: How to "unload" a library that was loaded. |
| 43 | * Hooks for Loading:: Providing code to be run when |
| 44 | particular libraries are loaded. |
| 45 | @end menu |
| 46 | |
| 47 | @node How Programs Do Loading |
| 48 | @section How Programs Do Loading |
| 49 | |
| 50 | Emacs Lisp has several interfaces for loading. For example, |
| 51 | @code{autoload} creates a placeholder object for a function defined in a |
| 52 | file; trying to call the autoloading function loads the file to get the |
| 53 | function's real definition (@pxref{Autoload}). @code{require} loads a |
| 54 | file if it isn't already loaded (@pxref{Named Features}). Ultimately, |
| 55 | all these facilities call the @code{load} function to do the work. |
| 56 | |
| 57 | @defun load filename &optional missing-ok nomessage nosuffix must-suffix |
| 58 | This function finds and opens a file of Lisp code, evaluates all the |
| 59 | forms in it, and closes the file. |
| 60 | |
| 61 | To find the file, @code{load} first looks for a file named |
| 62 | @file{@var{filename}.elc}, that is, for a file whose name is |
| 63 | @var{filename} with the extension @samp{.elc} appended. If such a |
| 64 | file exists, it is loaded. If there is no file by that name, then |
| 65 | @code{load} looks for a file named @file{@var{filename}.el}. If that |
| 66 | file exists, it is loaded. Finally, if neither of those names is |
| 67 | found, @code{load} looks for a file named @var{filename} with nothing |
| 68 | appended, and loads it if it exists. (The @code{load} function is not |
| 69 | clever about looking at @var{filename}. In the perverse case of a |
| 70 | file named @file{foo.el.el}, evaluation of @code{(load "foo.el")} will |
| 71 | indeed find it.) |
| 72 | |
| 73 | If Auto Compression mode is enabled, as it is by default, then if |
| 74 | @code{load} can not find a file, it searches for a compressed version |
| 75 | of the file before trying other file names. It decompresses and loads |
| 76 | it if it exists. It looks for compressed versions by appending each |
| 77 | of the suffixes in @code{jka-compr-load-suffixes} to the file name. |
| 78 | The value of this variable must be a list of strings. Its standard |
| 79 | value is @code{(".gz")}. |
| 80 | |
| 81 | If the optional argument @var{nosuffix} is non-@code{nil}, then |
| 82 | @code{load} does not try the suffixes @samp{.elc} and @samp{.el}. In |
| 83 | this case, you must specify the precise file name you want, except |
| 84 | that, if Auto Compression mode is enabled, @code{load} will still use |
| 85 | @code{jka-compr-load-suffixes} to find compressed versions. By |
| 86 | specifying the precise file name and using @code{t} for |
| 87 | @var{nosuffix}, you can prevent file names like @file{foo.el.el} from |
| 88 | being tried. |
| 89 | |
| 90 | If the optional argument @var{must-suffix} is non-@code{nil}, then |
| 91 | @code{load} insists that the file name used must end in either |
| 92 | @samp{.el} or @samp{.elc} (possibly extended with a compression |
| 93 | suffix), unless it contains an explicit directory name. |
| 94 | |
| 95 | If @var{filename} is a relative file name, such as @file{foo} or |
| 96 | @file{baz/foo.bar}, @code{load} searches for the file using the variable |
| 97 | @code{load-path}. It appends @var{filename} to each of the directories |
| 98 | listed in @code{load-path}, and loads the first file it finds whose name |
| 99 | matches. The current default directory is tried only if it is specified |
| 100 | in @code{load-path}, where @code{nil} stands for the default directory. |
| 101 | @code{load} tries all three possible suffixes in the first directory in |
| 102 | @code{load-path}, then all three suffixes in the second directory, and |
| 103 | so on. @xref{Library Search}. |
| 104 | |
| 105 | Whatever the name under which the file is eventually found, and the |
| 106 | directory where Emacs found it, Emacs sets the value of the variable |
| 107 | @code{load-file-name} to that file's name. |
| 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 |
| 150 | @code{load}, except for the way it reads its argument interactively. |
| 151 | @xref{Lisp Libraries,,,emacs, The GNU Emacs Manual}. |
| 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-file-name |
| 160 | When Emacs is in the process of loading a file, this variable's value |
| 161 | is the name of that file, as Emacs found it during the search |
| 162 | described earlier in this section. |
| 163 | @end defvar |
| 164 | |
| 165 | @defvar load-read-function |
| 166 | @anchor{Definition of load-read-function} |
| 167 | @c do not allow page break at anchor; work around Texinfo deficiency. |
| 168 | This variable specifies an alternate expression-reading function for |
| 169 | @code{load} and @code{eval-region} to use instead of @code{read}. |
| 170 | The function should accept one argument, just as @code{read} does. |
| 171 | |
| 172 | Normally, the variable's value is @code{nil}, which means those |
| 173 | functions should use @code{read}. |
| 174 | |
| 175 | Instead of using this variable, it is cleaner to use another, newer |
| 176 | feature: to pass the function as the @var{read-function} argument to |
| 177 | @code{eval-region}. @xref{Definition of eval-region,, Eval}. |
| 178 | @end defvar |
| 179 | |
| 180 | For information about how @code{load} is used in building Emacs, see |
| 181 | @ref{Building Emacs}. |
| 182 | |
| 183 | @node Load Suffixes |
| 184 | @section Load Suffixes |
| 185 | We now describe some technical details about the exact suffixes that |
| 186 | @code{load} tries. |
| 187 | |
| 188 | @defvar load-suffixes |
| 189 | This is a list of suffixes indicating (compiled or source) Emacs Lisp |
| 190 | files. It should not include the empty string. @code{load} uses |
| 191 | these suffixes in order when it appends Lisp suffixes to the specified |
| 192 | file name. The standard value is @code{(".elc" ".el")} which produces |
| 193 | the behavior described in the previous section. |
| 194 | @end defvar |
| 195 | |
| 196 | @defvar load-file-rep-suffixes |
| 197 | This is a list of suffixes that indicate representations of the same |
| 198 | file. This list should normally start with the empty string. |
| 199 | When @code{load} searches for a file it appends the suffixes in this |
| 200 | list, in order, to the file name, before searching for another file. |
| 201 | |
| 202 | Enabling Auto Compression mode appends the suffixes in |
| 203 | @code{jka-compr-load-suffixes} to this list and disabling Auto |
| 204 | Compression mode removes them again. The standard value of |
| 205 | @code{load-file-rep-suffixes} if Auto Compression mode is disabled is |
| 206 | @code{("")}. Given that the standard value of |
| 207 | @code{jka-compr-load-suffixes} is @code{(".gz")}, the standard value |
| 208 | of @code{load-file-rep-suffixes} if Auto Compression mode is enabled |
| 209 | is @code{("" ".gz")}. |
| 210 | @end defvar |
| 211 | |
| 212 | @defun get-load-suffixes |
| 213 | This function returns the list of all suffixes that @code{load} should |
| 214 | try, in order, when its @var{must-suffix} argument is non-@code{nil}. |
| 215 | This takes both @code{load-suffixes} and @code{load-file-rep-suffixes} |
| 216 | into account. If @code{load-suffixes}, @code{jka-compr-load-suffixes} |
| 217 | and @code{load-file-rep-suffixes} all have their standard values, this |
| 218 | function returns @code{(".elc" ".elc.gz" ".el" ".el.gz")} if Auto |
| 219 | Compression mode is enabled and @code{(".elc" ".el")} if Auto |
| 220 | Compression mode is disabled. |
| 221 | @end defun |
| 222 | |
| 223 | To summarize, @code{load} normally first tries the suffixes in the |
| 224 | value of @code{(get-load-suffixes)} and then those in |
| 225 | @code{load-file-rep-suffixes}. If @var{nosuffix} is non-@code{nil}, |
| 226 | it skips the former group, and if @var{must-suffix} is non-@code{nil}, |
| 227 | it skips the latter group. |
| 228 | |
| 229 | @node Library Search |
| 230 | @section Library Search |
| 231 | @cindex library search |
| 232 | @cindex find library |
| 233 | |
| 234 | When Emacs loads a Lisp library, it searches for the library |
| 235 | in a list of directories specified by the variable @code{load-path}. |
| 236 | |
| 237 | @defvar load-path |
| 238 | @cindex @env{EMACSLOADPATH} environment variable |
| 239 | The value of this variable is a list of directories to search when |
| 240 | loading files with @code{load}. Each element is a string (which must be |
| 241 | a directory name) or @code{nil} (which stands for the current working |
| 242 | directory). |
| 243 | @end defvar |
| 244 | |
| 245 | Each time Emacs starts up, it sets up the value of @code{load-path} |
| 246 | in several steps. First, it initializes @code{load-path} to the |
| 247 | directories specified by the environment variable @env{EMACSLOADPATH}, |
| 248 | if that exists. The syntax of @env{EMACSLOADPATH} is the same as used |
| 249 | for @code{PATH}; directory names are separated by @samp{:} (or |
| 250 | @samp{;}, on some operating systems), and @samp{.} stands for the |
| 251 | current default directory. Here is an example of how to set |
| 252 | @env{EMACSLOADPATH} variable from @command{sh}: |
| 253 | |
| 254 | @smallexample |
| 255 | export EMACSLOADPATH |
| 256 | EMACSLOADPATH=/home/foo/.emacs.d/lisp:/opt/emacs/lisp |
| 257 | @end smallexample |
| 258 | |
| 259 | @noindent |
| 260 | Here is how to set it from @code{csh}: |
| 261 | |
| 262 | @smallexample |
| 263 | setenv EMACSLOADPATH /home/foo/.emacs.d/lisp:/opt/emacs/lisp |
| 264 | @end smallexample |
| 265 | |
| 266 | If @env{EMACSLOADPATH} is not set (which is usually the case), Emacs |
| 267 | initializes @code{load-path} with the following two directories: |
| 268 | |
| 269 | @smallexample |
| 270 | "/usr/local/share/emacs/@var{version}/site-lisp" |
| 271 | @end smallexample |
| 272 | |
| 273 | @noindent |
| 274 | and |
| 275 | |
| 276 | @smallexample |
| 277 | "/usr/local/share/emacs/site-lisp" |
| 278 | @end smallexample |
| 279 | |
| 280 | @noindent |
| 281 | The first one is for locally installed packages for a particular Emacs |
| 282 | version; the second is for locally installed packages meant for use |
| 283 | with all installed Emacs versions. |
| 284 | |
| 285 | If you run Emacs from the directory where it was built---that is, an |
| 286 | executable that has not been formally installed---Emacs puts two more |
| 287 | directories in @code{load-path}. These are the @code{lisp} and |
| 288 | @code{site-lisp} subdirectories of the main build directory. (Both |
| 289 | are represented as absolute file names.) |
| 290 | |
| 291 | Next, Emacs ``expands'' the initial list of directories in |
| 292 | @code{load-path} by adding the subdirectories of those directories. |
| 293 | Both immediate subdirectories and subdirectories multiple levels down |
| 294 | are added. But it excludes subdirectories whose names do not start |
| 295 | with a letter or digit, and subdirectories named @file{RCS} or |
| 296 | @file{CVS}, and subdirectories containing a file named |
| 297 | @file{.nosearch}. |
| 298 | |
| 299 | Next, Emacs adds any extra load directory that you specify using the |
| 300 | @samp{-L} command-line option (@pxref{Action Arguments,,,emacs, The |
| 301 | GNU Emacs Manual}). It also adds the directories where optional |
| 302 | packages are installed, if any (@pxref{Packaging Basics}). |
| 303 | |
| 304 | It is common to add code to one's init file (@pxref{Init File}) to |
| 305 | add one or more directories to @code{load-path}. For example: |
| 306 | |
| 307 | @smallexample |
| 308 | (push "~/.emacs.d/lisp" load-path) |
| 309 | @end smallexample |
| 310 | |
| 311 | Dumping Emacs uses a special value of @code{load-path}. If the |
| 312 | value of @code{load-path} at the end of dumping is unchanged (that is, |
| 313 | still the same special value), the dumped Emacs switches to the |
| 314 | ordinary @code{load-path} value when it starts up, as described above. |
| 315 | But if @code{load-path} has any other value at the end of dumping, |
| 316 | that value is used for execution of the dumped Emacs also. |
| 317 | |
| 318 | @deffn Command locate-library library &optional nosuffix path interactive-call |
| 319 | This command finds the precise file name for library @var{library}. It |
| 320 | searches for the library in the same way @code{load} does, and the |
| 321 | argument @var{nosuffix} has the same meaning as in @code{load}: don't |
| 322 | add suffixes @samp{.elc} or @samp{.el} to the specified name |
| 323 | @var{library}. |
| 324 | |
| 325 | If the @var{path} is non-@code{nil}, that list of directories is used |
| 326 | instead of @code{load-path}. |
| 327 | |
| 328 | When @code{locate-library} is called from a program, it returns the file |
| 329 | name as a string. When the user runs @code{locate-library} |
| 330 | interactively, the argument @var{interactive-call} is @code{t}, and this |
| 331 | tells @code{locate-library} to display the file name in the echo area. |
| 332 | @end deffn |
| 333 | |
| 334 | @cindex shadowed Lisp files |
| 335 | @deffn Command list-load-path-shadows &optional stringp |
| 336 | This command shows a list of @dfn{shadowed} Emacs Lisp files. A |
| 337 | shadowed file is one that will not normally be loaded, despite being |
| 338 | in a directory on @code{load-path}, due to the existence of another |
| 339 | similarly-named file in a directory earlier on @code{load-path}. |
| 340 | |
| 341 | For instance, suppose @code{load-path} is set to |
| 342 | |
| 343 | @smallexample |
| 344 | ("/opt/emacs/site-lisp" "/usr/share/emacs/23.3/lisp") |
| 345 | @end smallexample |
| 346 | |
| 347 | @noindent |
| 348 | and that both these directories contain a file named @file{foo.el}. |
| 349 | Then @code{(require 'foo)} never loads the file in the second |
| 350 | directory. Such a situation might indicate a problem in the way Emacs |
| 351 | was installed. |
| 352 | |
| 353 | When called from Lisp, this function prints a message listing the |
| 354 | shadowed files, instead of displaying them in a buffer. If the |
| 355 | optional argument @code{stringp} is non-@code{nil}, it instead returns |
| 356 | the shadowed files as a string. |
| 357 | @end deffn |
| 358 | |
| 359 | @node Loading Non-ASCII |
| 360 | @section Loading Non-@acronym{ASCII} Characters |
| 361 | |
| 362 | When Emacs Lisp programs contain string constants with non-@acronym{ASCII} |
| 363 | characters, these can be represented within Emacs either as unibyte |
| 364 | strings or as multibyte strings (@pxref{Text Representations}). Which |
| 365 | representation is used depends on how the file is read into Emacs. If |
| 366 | it is read with decoding into multibyte representation, the text of the |
| 367 | Lisp program will be multibyte text, and its string constants will be |
| 368 | multibyte strings. If a file containing Latin-1 characters (for |
| 369 | example) is read without decoding, the text of the program will be |
| 370 | unibyte text, and its string constants will be unibyte strings. |
| 371 | @xref{Coding Systems}. |
| 372 | |
| 373 | In most Emacs Lisp programs, the fact that non-@acronym{ASCII} |
| 374 | strings are multibyte strings should not be noticeable, since |
| 375 | inserting them in unibyte buffers converts them to unibyte |
| 376 | automatically. However, if this does make a difference, you can force |
| 377 | a particular Lisp file to be interpreted as unibyte by writing |
| 378 | @samp{unibyte: t} in a local variables section. With |
| 379 | that designator, the file will unconditionally be interpreted as |
| 380 | unibyte, even in an ordinary multibyte Emacs session. This can matter |
| 381 | when making keybindings to non-@acronym{ASCII} characters written as |
| 382 | @code{?v@var{literal}}. |
| 383 | |
| 384 | @node Autoload |
| 385 | @section Autoload |
| 386 | @cindex autoload |
| 387 | |
| 388 | The @dfn{autoload} facility allows you to register the existence of |
| 389 | a function or macro, but put off loading the file that defines it. |
| 390 | The first call to the function automatically reads the proper file, in |
| 391 | order to install the real definition and other associated code, then |
| 392 | runs the real definition as if it had been loaded all along. |
| 393 | |
| 394 | There are two ways to set up an autoloaded function: by calling |
| 395 | @code{autoload}, and by writing a special ``magic'' comment in the |
| 396 | source before the real definition. @code{autoload} is the low-level |
| 397 | primitive for autoloading; any Lisp program can call @code{autoload} at |
| 398 | any time. Magic comments are the most convenient way to make a function |
| 399 | autoload, for packages installed along with Emacs. These comments do |
| 400 | nothing on their own, but they serve as a guide for the command |
| 401 | @code{update-file-autoloads}, which constructs calls to @code{autoload} |
| 402 | and arranges to execute them when Emacs is built. |
| 403 | |
| 404 | @defun autoload function filename &optional docstring interactive type |
| 405 | This function defines the function (or macro) named @var{function} so as |
| 406 | to load automatically from @var{filename}. The string @var{filename} |
| 407 | specifies the file to load to get the real definition of @var{function}. |
| 408 | |
| 409 | If @var{filename} does not contain either a directory name, or the |
| 410 | suffix @code{.el} or @code{.elc}, then @code{autoload} insists on adding |
| 411 | one of these suffixes, and it will not load from a file whose name is |
| 412 | just @var{filename} with no added suffix. (The variable |
| 413 | @code{load-suffixes} specifies the exact required suffixes.) |
| 414 | |
| 415 | The argument @var{docstring} is the documentation string for the |
| 416 | function. Specifying the documentation string in the call to |
| 417 | @code{autoload} makes it possible to look at the documentation without |
| 418 | loading the function's real definition. Normally, this should be |
| 419 | identical to the documentation string in the function definition |
| 420 | itself. If it isn't, the function definition's documentation string |
| 421 | takes effect when it is loaded. |
| 422 | |
| 423 | If @var{interactive} is non-@code{nil}, that says @var{function} can be |
| 424 | called interactively. This lets completion in @kbd{M-x} work without |
| 425 | loading @var{function}'s real definition. The complete interactive |
| 426 | specification is not given here; it's not needed unless the user |
| 427 | actually calls @var{function}, and when that happens, it's time to load |
| 428 | the real definition. |
| 429 | |
| 430 | You can autoload macros and keymaps as well as ordinary functions. |
| 431 | Specify @var{type} as @code{macro} if @var{function} is really a macro. |
| 432 | Specify @var{type} as @code{keymap} if @var{function} is really a |
| 433 | keymap. Various parts of Emacs need to know this information without |
| 434 | loading the real definition. |
| 435 | |
| 436 | An autoloaded keymap loads automatically during key lookup when a prefix |
| 437 | key's binding is the symbol @var{function}. Autoloading does not occur |
| 438 | for other kinds of access to the keymap. In particular, it does not |
| 439 | happen when a Lisp program gets the keymap from the value of a variable |
| 440 | and calls @code{define-key}; not even if the variable name is the same |
| 441 | symbol @var{function}. |
| 442 | |
| 443 | @cindex function cell in autoload |
| 444 | If @var{function} already has a non-void function definition that is not |
| 445 | an autoload object, @code{autoload} does nothing and returns @code{nil}. |
| 446 | If the function cell of @var{function} is void, or is already an autoload |
| 447 | object, then it is defined as an autoload object like this: |
| 448 | |
| 449 | @example |
| 450 | (autoload @var{filename} @var{docstring} @var{interactive} @var{type}) |
| 451 | @end example |
| 452 | |
| 453 | For example, |
| 454 | |
| 455 | @example |
| 456 | @group |
| 457 | (symbol-function 'run-prolog) |
| 458 | @result{} (autoload "prolog" 169681 t nil) |
| 459 | @end group |
| 460 | @end example |
| 461 | |
| 462 | @noindent |
| 463 | In this case, @code{"prolog"} is the name of the file to load, 169681 |
| 464 | refers to the documentation string in the |
| 465 | @file{emacs/etc/DOC-@var{version}} file (@pxref{Documentation Basics}), |
| 466 | @code{t} means the function is interactive, and @code{nil} that it is |
| 467 | not a macro or a keymap. |
| 468 | @end defun |
| 469 | |
| 470 | @cindex autoload errors |
| 471 | The autoloaded file usually contains other definitions and may require |
| 472 | or provide one or more features. If the file is not completely loaded |
| 473 | (due to an error in the evaluation of its contents), any function |
| 474 | definitions or @code{provide} calls that occurred during the load are |
| 475 | undone. This is to ensure that the next attempt to call any function |
| 476 | autoloading from this file will try again to load the file. If not for |
| 477 | this, then some of the functions in the file might be defined by the |
| 478 | aborted load, but fail to work properly for the lack of certain |
| 479 | subroutines not loaded successfully because they come later in the file. |
| 480 | |
| 481 | If the autoloaded file fails to define the desired Lisp function or |
| 482 | macro, then an error is signaled with data @code{"Autoloading failed to |
| 483 | define function @var{function-name}"}. |
| 484 | |
| 485 | @findex update-file-autoloads |
| 486 | @findex update-directory-autoloads |
| 487 | @cindex magic autoload comment |
| 488 | @cindex autoload cookie |
| 489 | @anchor{autoload cookie} |
| 490 | A magic autoload comment (often called an @dfn{autoload cookie}) |
| 491 | consists of @samp{;;;###autoload}, on a line by itself, |
| 492 | just before the real definition of the function in its |
| 493 | autoloadable source file. The command @kbd{M-x update-file-autoloads} |
| 494 | writes a corresponding @code{autoload} call into @file{loaddefs.el}. |
| 495 | (The string that serves as the autoload cookie and the name of the |
| 496 | file generated by @code{update-file-autoloads} can be changed from the |
| 497 | above defaults, see below.) |
| 498 | Building Emacs loads @file{loaddefs.el} and thus calls @code{autoload}. |
| 499 | @kbd{M-x update-directory-autoloads} is even more powerful; it updates |
| 500 | autoloads for all files in the current directory. |
| 501 | |
| 502 | The same magic comment can copy any kind of form into |
| 503 | @file{loaddefs.el}. The form following the magic comment is copied |
| 504 | verbatim, @emph{except} if it is one of the forms which the autoload |
| 505 | facility handles specially (e.g.@: by conversion into an |
| 506 | @code{autoload} call). The forms which are not copied verbatim are |
| 507 | the following: |
| 508 | |
| 509 | @table @asis |
| 510 | @item Definitions for function or function-like objects: |
| 511 | @code{defun} and @code{defmacro}; also @code{defun*} and |
| 512 | @code{defmacro*} (@pxref{Argument Lists,,,cl,CL Manual}), and |
| 513 | @code{define-overloadable-function} (see the commentary in |
| 514 | @file{mode-local.el}). |
| 515 | |
| 516 | @item Definitions for major or minor modes: |
| 517 | @code{define-derived-mode}, @code{define-minor-mode}, |
| 518 | @code{define-compilation-mode}, @code{define-generic-mode}, |
| 519 | @code{easy-mmode-define-global-mode}, @code{define-global-minor-mode}, |
| 520 | @code{define-globalized-minor-mode}, and |
| 521 | @code{easy-mmode-define-minor-mode}. |
| 522 | |
| 523 | @item Other definition types: |
| 524 | @code{defcustom}, @code{defgroup}, @code{defclass} |
| 525 | (@pxref{Top,EIEIO,,eieio,EIEIO}), and @code{define-skeleton} (see the |
| 526 | commentary in @file{skeleton.el}). |
| 527 | @end table |
| 528 | |
| 529 | You can also use a magic comment to execute a form at build time |
| 530 | @emph{without} executing it when the file itself is loaded. To do this, |
| 531 | write the form @emph{on the same line} as the magic comment. Since it |
| 532 | is in a comment, it does nothing when you load the source file; but |
| 533 | @kbd{M-x update-file-autoloads} copies it to @file{loaddefs.el}, where |
| 534 | it is executed while building Emacs. |
| 535 | |
| 536 | The following example shows how @code{doctor} is prepared for |
| 537 | autoloading with a magic comment: |
| 538 | |
| 539 | @smallexample |
| 540 | ;;;###autoload |
| 541 | (defun doctor () |
| 542 | "Switch to *doctor* buffer and start giving psychotherapy." |
| 543 | (interactive) |
| 544 | (switch-to-buffer "*doctor*") |
| 545 | (doctor-mode)) |
| 546 | @end smallexample |
| 547 | |
| 548 | @noindent |
| 549 | Here's what that produces in @file{loaddefs.el}: |
| 550 | |
| 551 | @smallexample |
| 552 | (autoload (quote doctor) "doctor" "\ |
| 553 | Switch to *doctor* buffer and start giving psychotherapy. |
| 554 | |
| 555 | \(fn)" t nil) |
| 556 | @end smallexample |
| 557 | |
| 558 | @noindent |
| 559 | @cindex @code{fn} in function's documentation string |
| 560 | The backslash and newline immediately following the double-quote are a |
| 561 | convention used only in the preloaded uncompiled Lisp files such as |
| 562 | @file{loaddefs.el}; they tell @code{make-docfile} to put the |
| 563 | documentation string in the @file{etc/DOC} file. @xref{Building Emacs}. |
| 564 | See also the commentary in @file{lib-src/make-docfile.c}. @samp{(fn)} |
| 565 | in the usage part of the documentation string is replaced with the |
| 566 | function's name when the various help functions (@pxref{Help |
| 567 | Functions}) display it. |
| 568 | |
| 569 | If you write a function definition with an unusual macro that is not |
| 570 | one of the known and recognized function definition methods, use of an |
| 571 | ordinary magic autoload comment would copy the whole definition into |
| 572 | @code{loaddefs.el}. That is not desirable. You can put the desired |
| 573 | @code{autoload} call into @code{loaddefs.el} instead by writing this: |
| 574 | |
| 575 | @smallexample |
| 576 | ;;;###autoload (autoload 'foo "myfile") |
| 577 | (mydefunmacro foo |
| 578 | ...) |
| 579 | @end smallexample |
| 580 | |
| 581 | You can use a non-default string as the autoload cookie and have the |
| 582 | corresponding autoload calls written into a file whose name is |
| 583 | different from the default @file{loaddefs.el}. Emacs provides two |
| 584 | variables to control this: |
| 585 | |
| 586 | @defvar generate-autoload-cookie |
| 587 | The value of this variable should be a string whose syntax is a Lisp |
| 588 | comment. @kbd{M-x update-file-autoloads} copies the Lisp form that |
| 589 | follows the cookie into the autoload file it generates. The default |
| 590 | value of this variable is @code{";;;###autoload"}. |
| 591 | @end defvar |
| 592 | |
| 593 | @defvar generated-autoload-file |
| 594 | The value of this variable names an Emacs Lisp file where the autoload |
| 595 | calls should go. The default value is @file{loaddefs.el}, but you can |
| 596 | override that, e.g., in the ``Local Variables'' section of a |
| 597 | @file{.el} file (@pxref{File Local Variables}). The autoload file is |
| 598 | assumed to contain a trailer starting with a formfeed character. |
| 599 | @end defvar |
| 600 | |
| 601 | @node Repeated Loading |
| 602 | @section Repeated Loading |
| 603 | @cindex repeated loading |
| 604 | |
| 605 | You can load a given file more than once in an Emacs session. For |
| 606 | example, after you have rewritten and reinstalled a function definition |
| 607 | by editing it in a buffer, you may wish to return to the original |
| 608 | version; you can do this by reloading the file it came from. |
| 609 | |
| 610 | When you load or reload files, bear in mind that the @code{load} and |
| 611 | @code{load-library} functions automatically load a byte-compiled file |
| 612 | rather than a non-compiled file of similar name. If you rewrite a file |
| 613 | that you intend to save and reinstall, you need to byte-compile the new |
| 614 | version; otherwise Emacs will load the older, byte-compiled file instead |
| 615 | of your newer, non-compiled file! If that happens, the message |
| 616 | displayed when loading the file includes, @samp{(compiled; note, source is |
| 617 | newer)}, to remind you to recompile it. |
| 618 | |
| 619 | When writing the forms in a Lisp library file, keep in mind that the |
| 620 | file might be loaded more than once. For example, think about whether |
| 621 | each variable should be reinitialized when you reload the library; |
| 622 | @code{defvar} does not change the value if the variable is already |
| 623 | initialized. (@xref{Defining Variables}.) |
| 624 | |
| 625 | The simplest way to add an element to an alist is like this: |
| 626 | |
| 627 | @example |
| 628 | (push '(leif-mode " Leif") minor-mode-alist) |
| 629 | @end example |
| 630 | |
| 631 | @noindent |
| 632 | But this would add multiple elements if the library is reloaded. To |
| 633 | avoid the problem, use @code{add-to-list} (@pxref{List Variables}): |
| 634 | |
| 635 | @example |
| 636 | (add-to-list 'minor-mode-alist '(leif-mode " Leif")) |
| 637 | @end example |
| 638 | |
| 639 | Occasionally you will want to test explicitly whether a library has |
| 640 | already been loaded. If the library uses @code{provide} to provide a |
| 641 | named feature, you can use @code{featurep} earlier in the file to test |
| 642 | whether the @code{provide} call has been executed before (@pxref{Named |
| 643 | Features}). Alternatively, you could use something like this: |
| 644 | |
| 645 | @example |
| 646 | (defvar foo-was-loaded nil) |
| 647 | |
| 648 | (unless foo-was-loaded |
| 649 | @var{execute-first-time-only} |
| 650 | (setq foo-was-loaded t)) |
| 651 | @end example |
| 652 | |
| 653 | @noindent |
| 654 | |
| 655 | @node Named Features |
| 656 | @section Features |
| 657 | @cindex features |
| 658 | @cindex requiring features |
| 659 | @cindex providing features |
| 660 | |
| 661 | @code{provide} and @code{require} are an alternative to |
| 662 | @code{autoload} for loading files automatically. They work in terms of |
| 663 | named @dfn{features}. Autoloading is triggered by calling a specific |
| 664 | function, but a feature is loaded the first time another program asks |
| 665 | for it by name. |
| 666 | |
| 667 | A feature name is a symbol that stands for a collection of functions, |
| 668 | variables, etc. The file that defines them should @dfn{provide} the |
| 669 | feature. Another program that uses them may ensure they are defined by |
| 670 | @dfn{requiring} the feature. This loads the file of definitions if it |
| 671 | hasn't been loaded already. |
| 672 | |
| 673 | @cindex load error with require |
| 674 | To require the presence of a feature, call @code{require} with the |
| 675 | feature name as argument. @code{require} looks in the global variable |
| 676 | @code{features} to see whether the desired feature has been provided |
| 677 | already. If not, it loads the feature from the appropriate file. This |
| 678 | file should call @code{provide} at the top level to add the feature to |
| 679 | @code{features}; if it fails to do so, @code{require} signals an error. |
| 680 | |
| 681 | For example, in @file{idlwave.el}, the definition for |
| 682 | @code{idlwave-complete-filename} includes the following code: |
| 683 | |
| 684 | @smallexample |
| 685 | (defun idlwave-complete-filename () |
| 686 | "Use the comint stuff to complete a file name." |
| 687 | (require 'comint) |
| 688 | (let* ((comint-file-name-chars "~/A-Za-z0-9+@:_.$#%=@{@}\\-") |
| 689 | (comint-completion-addsuffix nil) |
| 690 | ...) |
| 691 | (comint-dynamic-complete-filename))) |
| 692 | @end smallexample |
| 693 | |
| 694 | @noindent |
| 695 | The expression @code{(require 'comint)} loads the file @file{comint.el} |
| 696 | if it has not yet been loaded, ensuring that |
| 697 | @code{comint-dynamic-complete-filename} is defined. Features are |
| 698 | normally named after the files that provide them, so that |
| 699 | @code{require} need not be given the file name. (Note that it is |
| 700 | important that the @code{require} statement be outside the body of the |
| 701 | @code{let}. Loading a library while its variables are let-bound can |
| 702 | have unintended consequences, namely the variables becoming unbound |
| 703 | after the let exits.) |
| 704 | |
| 705 | The @file{comint.el} file contains the following top-level expression: |
| 706 | |
| 707 | @smallexample |
| 708 | (provide 'comint) |
| 709 | @end smallexample |
| 710 | |
| 711 | @noindent |
| 712 | This adds @code{comint} to the global @code{features} list, so that |
| 713 | @code{(require 'comint)} will henceforth know that nothing needs to be |
| 714 | done. |
| 715 | |
| 716 | @cindex byte-compiling @code{require} |
| 717 | When @code{require} is used at top level in a file, it takes effect |
| 718 | when you byte-compile that file (@pxref{Byte Compilation}) as well as |
| 719 | when you load it. This is in case the required package contains macros |
| 720 | that the byte compiler must know about. It also avoids byte compiler |
| 721 | warnings for functions and variables defined in the file loaded with |
| 722 | @code{require}. |
| 723 | |
| 724 | Although top-level calls to @code{require} are evaluated during |
| 725 | byte compilation, @code{provide} calls are not. Therefore, you can |
| 726 | ensure that a file of definitions is loaded before it is byte-compiled |
| 727 | by including a @code{provide} followed by a @code{require} for the same |
| 728 | feature, as in the following example. |
| 729 | |
| 730 | @smallexample |
| 731 | @group |
| 732 | (provide 'my-feature) ; @r{Ignored by byte compiler,} |
| 733 | ; @r{evaluated by @code{load}.} |
| 734 | (require 'my-feature) ; @r{Evaluated by byte compiler.} |
| 735 | @end group |
| 736 | @end smallexample |
| 737 | |
| 738 | @noindent |
| 739 | The compiler ignores the @code{provide}, then processes the |
| 740 | @code{require} by loading the file in question. Loading the file does |
| 741 | execute the @code{provide} call, so the subsequent @code{require} call |
| 742 | does nothing when the file is loaded. |
| 743 | |
| 744 | @defun provide feature &optional subfeatures |
| 745 | This function announces that @var{feature} is now loaded, or being |
| 746 | loaded, into the current Emacs session. This means that the facilities |
| 747 | associated with @var{feature} are or will be available for other Lisp |
| 748 | programs. |
| 749 | |
| 750 | The direct effect of calling @code{provide} is if not already in |
| 751 | @var{features} then to add @var{feature} to the front of that list and |
| 752 | call any @code{eval-after-load} code waiting for it (@pxref{Hooks for |
| 753 | Loading}). The argument @var{feature} must be a symbol. |
| 754 | @code{provide} returns @var{feature}. |
| 755 | |
| 756 | If provided, @var{subfeatures} should be a list of symbols indicating |
| 757 | a set of specific subfeatures provided by this version of |
| 758 | @var{feature}. You can test the presence of a subfeature using |
| 759 | @code{featurep}. The idea of subfeatures is that you use them when a |
| 760 | package (which is one @var{feature}) is complex enough to make it |
| 761 | useful to give names to various parts or functionalities of the |
| 762 | package, which might or might not be loaded, or might or might not be |
| 763 | present in a given version. @xref{Network Feature Testing}, for |
| 764 | an example. |
| 765 | |
| 766 | @smallexample |
| 767 | features |
| 768 | @result{} (bar bish) |
| 769 | |
| 770 | (provide 'foo) |
| 771 | @result{} foo |
| 772 | features |
| 773 | @result{} (foo bar bish) |
| 774 | @end smallexample |
| 775 | |
| 776 | When a file is loaded to satisfy an autoload, and it stops due to an |
| 777 | error in the evaluation of its contents, any function definitions or |
| 778 | @code{provide} calls that occurred during the load are undone. |
| 779 | @xref{Autoload}. |
| 780 | @end defun |
| 781 | |
| 782 | @defun require feature &optional filename noerror |
| 783 | This function checks whether @var{feature} is present in the current |
| 784 | Emacs session (using @code{(featurep @var{feature})}; see below). The |
| 785 | argument @var{feature} must be a symbol. |
| 786 | |
| 787 | If the feature is not present, then @code{require} loads @var{filename} |
| 788 | with @code{load}. If @var{filename} is not supplied, then the name of |
| 789 | the symbol @var{feature} is used as the base file name to load. |
| 790 | However, in this case, @code{require} insists on finding @var{feature} |
| 791 | with an added @samp{.el} or @samp{.elc} suffix (possibly extended with |
| 792 | a compression suffix); a file whose name is just @var{feature} won't |
| 793 | be used. (The variable @code{load-suffixes} specifies the exact |
| 794 | required Lisp suffixes.) |
| 795 | |
| 796 | If @var{noerror} is non-@code{nil}, that suppresses errors from actual |
| 797 | loading of the file. In that case, @code{require} returns @code{nil} |
| 798 | if loading the file fails. Normally, @code{require} returns |
| 799 | @var{feature}. |
| 800 | |
| 801 | If loading the file succeeds but does not provide @var{feature}, |
| 802 | @code{require} signals an error, @samp{Required feature @var{feature} |
| 803 | was not provided}. |
| 804 | @end defun |
| 805 | |
| 806 | @defun featurep feature &optional subfeature |
| 807 | This function returns @code{t} if @var{feature} has been provided in |
| 808 | the current Emacs session (i.e.@:, if @var{feature} is a member of |
| 809 | @code{features}.) If @var{subfeature} is non-@code{nil}, then the |
| 810 | function returns @code{t} only if that subfeature is provided as well |
| 811 | (i.e.@: if @var{subfeature} is a member of the @code{subfeature} |
| 812 | property of the @var{feature} symbol.) |
| 813 | @end defun |
| 814 | |
| 815 | @defvar features |
| 816 | The value of this variable is a list of symbols that are the features |
| 817 | loaded in the current Emacs session. Each symbol was put in this list |
| 818 | with a call to @code{provide}. The order of the elements in the |
| 819 | @code{features} list is not significant. |
| 820 | @end defvar |
| 821 | |
| 822 | @node Where Defined |
| 823 | @section Which File Defined a Certain Symbol |
| 824 | |
| 825 | @defun symbol-file symbol &optional type |
| 826 | This function returns the name of the file that defined @var{symbol}. |
| 827 | If @var{type} is @code{nil}, then any kind of definition is acceptable. |
| 828 | If @var{type} is @code{defun}, @code{defvar}, or @code{defface}, that |
| 829 | specifies function definition, variable definition, or face definition |
| 830 | only. |
| 831 | |
| 832 | The value is normally an absolute file name. It can also be @code{nil}, |
| 833 | if the definition is not associated with any file. If @var{symbol} |
| 834 | specifies an autoloaded function, the value can be a relative file name |
| 835 | without extension. |
| 836 | @end defun |
| 837 | |
| 838 | The basis for @code{symbol-file} is the data in the variable |
| 839 | @code{load-history}. |
| 840 | |
| 841 | @defvar load-history |
| 842 | The value of this variable is an alist that associates the names of |
| 843 | loaded library files with the names of the functions and variables |
| 844 | they defined, as well as the features they provided or required. |
| 845 | |
| 846 | Each element in this alist describes one loaded library (including |
| 847 | libraries that are preloaded at startup). It is a list whose @sc{car} |
| 848 | is the absolute file name of the library (a string). The rest of the |
| 849 | list elements have these forms: |
| 850 | |
| 851 | @table @code |
| 852 | @item @var{var} |
| 853 | The symbol @var{var} was defined as a variable. |
| 854 | @item (defun . @var{fun}) |
| 855 | The function @var{fun} was defined. |
| 856 | @item (t . @var{fun}) |
| 857 | The function @var{fun} was previously an autoload before this library |
| 858 | redefined it as a function. The following element is always |
| 859 | @code{(defun . @var{fun})}, which represents defining @var{fun} as a |
| 860 | function. |
| 861 | @item (autoload . @var{fun}) |
| 862 | The function @var{fun} was defined as an autoload. |
| 863 | @item (defface . @var{face}) |
| 864 | The face @var{face} was defined. |
| 865 | @item (require . @var{feature}) |
| 866 | The feature @var{feature} was required. |
| 867 | @item (provide . @var{feature}) |
| 868 | The feature @var{feature} was provided. |
| 869 | @end table |
| 870 | |
| 871 | The value of @code{load-history} may have one element whose @sc{car} is |
| 872 | @code{nil}. This element describes definitions made with |
| 873 | @code{eval-buffer} on a buffer that is not visiting a file. |
| 874 | @end defvar |
| 875 | |
| 876 | The command @code{eval-region} updates @code{load-history}, but does so |
| 877 | by adding the symbols defined to the element for the file being visited, |
| 878 | rather than replacing that element. @xref{Eval}. |
| 879 | |
| 880 | @node Unloading |
| 881 | @section Unloading |
| 882 | @cindex unloading packages |
| 883 | |
| 884 | @c Emacs 19 feature |
| 885 | You can discard the functions and variables loaded by a library to |
| 886 | reclaim memory for other Lisp objects. To do this, use the function |
| 887 | @code{unload-feature}: |
| 888 | |
| 889 | @deffn Command unload-feature feature &optional force |
| 890 | This command unloads the library that provided feature @var{feature}. |
| 891 | It undefines all functions, macros, and variables defined in that |
| 892 | library with @code{defun}, @code{defalias}, @code{defsubst}, |
| 893 | @code{defmacro}, @code{defconst}, @code{defvar}, and @code{defcustom}. |
| 894 | It then restores any autoloads formerly associated with those symbols. |
| 895 | (Loading saves these in the @code{autoload} property of the symbol.) |
| 896 | |
| 897 | Before restoring the previous definitions, @code{unload-feature} runs |
| 898 | @code{remove-hook} to remove functions in the library from certain |
| 899 | hooks. These hooks include variables whose names end in @samp{hook} |
| 900 | or @samp{-hooks}, plus those listed in |
| 901 | @code{unload-feature-special-hooks}, as well as |
| 902 | @code{auto-mode-alist}. This is to prevent Emacs from ceasing to |
| 903 | function because important hooks refer to functions that are no longer |
| 904 | defined. |
| 905 | |
| 906 | Standard unloading activities also undoes ELP profiling of functions |
| 907 | in that library, unprovides any features provided by the library, and |
| 908 | cancels timers held in variables defined by the library. |
| 909 | |
| 910 | @vindex @var{feature}-unload-function |
| 911 | If these measures are not sufficient to prevent malfunction, a library |
| 912 | can define an explicit unloader named @code{@var{feature}-unload-function}. |
| 913 | If that symbol is defined as a function, @code{unload-feature} calls |
| 914 | it with no arguments before doing anything else. It can do whatever |
| 915 | is appropriate to unload the library. If it returns @code{nil}, |
| 916 | @code{unload-feature} proceeds to take the normal unload actions. |
| 917 | Otherwise it considers the job to be done. |
| 918 | |
| 919 | Ordinarily, @code{unload-feature} refuses to unload a library on which |
| 920 | other loaded libraries depend. (A library @var{a} depends on library |
| 921 | @var{b} if @var{a} contains a @code{require} for @var{b}.) If the |
| 922 | optional argument @var{force} is non-@code{nil}, dependencies are |
| 923 | ignored and you can unload any library. |
| 924 | @end deffn |
| 925 | |
| 926 | The @code{unload-feature} function is written in Lisp; its actions are |
| 927 | based on the variable @code{load-history}. |
| 928 | |
| 929 | @defvar unload-feature-special-hooks |
| 930 | This variable holds a list of hooks to be scanned before unloading a |
| 931 | library, to remove functions defined in the library. |
| 932 | @end defvar |
| 933 | |
| 934 | @node Hooks for Loading |
| 935 | @section Hooks for Loading |
| 936 | @cindex loading hooks |
| 937 | @cindex hooks for loading |
| 938 | |
| 939 | You can ask for code to be executed each time Emacs loads a library, |
| 940 | by using the variable @code{after-load-functions}: |
| 941 | |
| 942 | @defvar after-load-functions |
| 943 | This abnormal hook is run after loading a file. Each function in the |
| 944 | hook is called with a single argument, the absolute filename of the |
| 945 | file that was just loaded. |
| 946 | @end defvar |
| 947 | |
| 948 | If you want code to be executed when a @emph{particular} library is |
| 949 | loaded, use the function @code{eval-after-load}: |
| 950 | |
| 951 | @defun eval-after-load library form |
| 952 | This function arranges to evaluate @var{form} at the end of loading |
| 953 | the file @var{library}, each time @var{library} is loaded. If |
| 954 | @var{library} is already loaded, it evaluates @var{form} right away. |
| 955 | Don't forget to quote @var{form}! |
| 956 | |
| 957 | You don't need to give a directory or extension in the file name |
| 958 | @var{library}. Normally, you just give a bare file name, like this: |
| 959 | |
| 960 | @example |
| 961 | (eval-after-load "edebug" '(def-edebug-spec c-point t)) |
| 962 | @end example |
| 963 | |
| 964 | To restrict which files can trigger the evaluation, include a |
| 965 | directory or an extension or both in @var{library}. Only a file whose |
| 966 | absolute true name (i.e., the name with all symbolic links chased out) |
| 967 | matches all the given name components will match. In the following |
| 968 | example, @file{my_inst.elc} or @file{my_inst.elc.gz} in some directory |
| 969 | @code{..../foo/bar} will trigger the evaluation, but not |
| 970 | @file{my_inst.el}: |
| 971 | |
| 972 | @example |
| 973 | (eval-after-load "foo/bar/my_inst.elc" @dots{}) |
| 974 | @end example |
| 975 | |
| 976 | @var{library} can also be a feature (i.e.@: a symbol), in which case |
| 977 | @var{form} is evaluated at the end of any file where |
| 978 | @code{(provide @var{library})} is called. |
| 979 | |
| 980 | An error in @var{form} does not undo the load, but does prevent |
| 981 | execution of the rest of @var{form}. |
| 982 | @end defun |
| 983 | |
| 984 | Normally, well-designed Lisp programs should not use |
| 985 | @code{eval-after-load}. If you need to examine and set the variables |
| 986 | defined in another library (those meant for outside use), you can do |
| 987 | it immediately---there is no need to wait until the library is loaded. |
| 988 | If you need to call functions defined by that library, you should load |
| 989 | the library, preferably with @code{require} (@pxref{Named Features}). |
| 990 | |
| 991 | @defvar after-load-alist |
| 992 | This variable stores an alist built by @code{eval-after-load}, |
| 993 | containing the expressions to evaluate when certain libraries are |
| 994 | loaded. Each element looks like this: |
| 995 | |
| 996 | @example |
| 997 | (@var{regexp-or-feature} @var{forms}@dots{}) |
| 998 | @end example |
| 999 | |
| 1000 | The key @var{regexp-or-feature} is either a regular expression or a |
| 1001 | symbol, and the value is a list of forms. The forms are evaluated |
| 1002 | when the key matches the absolute true name or feature name of the |
| 1003 | library being loaded. |
| 1004 | @end defvar |