(elisp)How Programs Do Loading
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 (Note: Autoload). `require' loads a file if it isn't already loaded (Note: 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 `.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. 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 the optional argument NOSUFFIX is non-`nil', then the suffixes `.elc' and `.el' are not tried. In this case, you must specify the precise file name you want. By specifying the precise file name and using `t' for NOSUFFIX, you can prevent perverse file names such as `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', unless it contains an explicit directory name. If FILENAME does not contain an explicit directory name, and does not end in a suffix, then `load' insists on adding one. 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. Note: Library Search. If you get a warning that `foo.elc' is older than `foo.el', it means you should consider recompiling `foo.el'. Note: Byte Compilation. When loading a source file (not compiled), `load' performs character set translation just as Emacs would do when visiting the file. Note: Coding Systems. 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. `load-path' is not used, and suffixes are not appended. 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 in how it reads its argument interactively. - 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-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. Normally, the variable's value is `nil', which means those functions should use `read'. *Note:* 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'. Note: Eval. For information about how `load' is used in building Emacs, see Note: Building Emacs.
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