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### 15.1 How Programs Do Loading

Emacs Lisp has several interfaces for loading. For example, `autoload` creates a placeholder object for a function defined in a file; trying to call the autoloading function loads the file to get the function’s real definition (see Autoload). `require` loads a file if it isn’t already loaded (see Named Features). Ultimately, all these facilities call the `load` function to do the work.

Function: load filename &optional missing-ok nomessage nosuffix must-suffix

  This function finds and opens a file of Lisp code, evaluates all the forms in it, and closes the file.

  To find the file, `load` first looks for a file named `filename.elc`, that is, for a file whose name is filename with the extension ‘`.elc`’ appended. If such a file exists, it is loaded. If there is no file by that name, then `load` looks for a file named `filename.el`. If that file exists, it is loaded. If Emacs was compiled with support for dynamic modules (see Dynamic Modules), `load` next looks for a file named `filename.ext`, where ext is a system-dependent file-name extension of shared libraries. Finally, if neither of those names is found, `load` looks for a file named filename with nothing appended, and loads it if it exists. (The `load` function is not clever about looking at filename. In the perverse case of a file named `foo.el.el`, evaluation of `(load "foo.el")` will indeed find it.)

  If Auto Compression mode is enabled, as it is by default, then if `load` can not find a file, it searches for a compressed version of the file before trying other file names. It decompresses and loads it if it exists. It looks for compressed versions by appending each of the suffixes in `jka-compr-load-suffixes` to the file name. The value of this variable must be a list of strings. Its standard value is `(".gz")`.

  If the optional argument nosuffix is non-`nil`, then `load` does not try the suffixes ‘`.elc`’ and ‘`.el`’. In this case, you must specify the precise file name you want, except that, if Auto Compression mode is enabled, `load` will still use `jka-compr-load-suffixes` to find compressed versions. By specifying the precise file name and using `t` for nosuffix, you can prevent file names like `foo.el.el` from being tried.

  If the optional argument must-suffix is non-`nil`, then `load` insists that the file name used must end in either ‘`.el`’ or ‘`.elc`’ (possibly extended with a compression suffix) or the shared-library extension, unless it contains an explicit directory name.

  If the option `load-prefer-newer` is non-`nil`, then when searching suffixes, `load` selects whichever version of a file (‘`.elc`’, ‘`.el`’, etc.) has been modified most recently.

  If filename is a relative file name, such as `foo` or `baz/foo.bar`, `load` searches for the file using the variable `load-path`. It appends filename to each of the directories listed in `load-path`, and loads the first file it finds whose name matches. The current default directory is tried only if it is specified in `load-path`, where `nil` stands for the default directory. `load` tries all three possible suffixes in the first directory in `load-path`, then all three suffixes in the second directory, and so on. See Library Search.

  Whatever the name under which the file is eventually found, and the directory where Emacs found it, Emacs sets the value of the variable `load-file-name` to that file’s name.

  If you get a warning that `foo.elc` is older than `foo.el`, it means you should consider recompiling `foo.el`. See Byte Compilation.

  When loading a source file (not compiled), `load` performs character set translation just as Emacs would do when visiting the file. See Coding Systems.

  When loading an uncompiled file, Emacs tries to expand any macros that the file contains (see Macros). We refer to this as eager macro expansion. Doing this (rather than deferring the expansion until the relevant code runs) can significantly speed up the execution of uncompiled code. Sometimes, this macro expansion cannot be done, owing to a cyclic dependency. In the simplest example of this, the file you are loading refers to a macro defined in another file, and that file in turn requires the file you are loading. This is generally harmless. Emacs prints a warning (‘`Eager macro-expansion skipped due to cycle…`’) giving details of the problem, but it still loads the file, just leaving the macro unexpanded for now. You may wish to restructure your code so that this does not happen. Loading a compiled file does not cause macroexpansion, because this should already have happened during compilation. See Compiling Macros.

  Messages like ‘`Loading foo...`’ and ‘`Loading foo...done`’ appear in the echo area during loading unless nomessage is non-`nil`.

  Any unhandled errors while loading a file terminate loading. If the load was done for the sake of `autoload`, any function definitions made during the loading are undone.

  If `load` can’t find the file to load, then normally it signals the error `file-error` (with ‘`Cannot open load file filename`’). But if missing-ok is non-`nil`, then `load` just returns `nil`.

  You can use the variable `load-read-function` to specify a function for `load` to use instead of `read` for reading expressions. See below.

  `load` returns `t` if the file loads successfully.

Command: load-file filename

  This command loads the file filename. If filename is a relative file name, then the current default directory is assumed. This command does not use `load-path`, and does not append suffixes. However, it does look for compressed versions (if Auto Compression Mode is enabled). Use this command if you wish to specify precisely the file name to load.

Command: load-library library

  This command loads the library named library. It is equivalent to `load`, except for the way it reads its argument interactively. See Lisp Libraries in The GNU Emacs Manual.

Variable: load-in-progress

  This variable is non-`nil` if Emacs is in the process of loading a file, and it is `nil` otherwise.

Variable: load-file-name

  When Emacs is in the process of loading a file, this variable’s value is the name of that file, as Emacs found it during the search described earlier in this section.

Variable: load-read-function

  This variable specifies an alternate expression-reading function for `load` and `eval-region` to use instead of `read`. The function should accept one argument, just as `read` does.

  By default, this variable’s value is `read`. See Input Functions.

  Instead of using this variable, it is cleaner to use another, newer feature: to pass the function as the read-function argument to `eval-region`. See Eval.

For information about how `load` is used in building Emacs, see Building Emacs.

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