(emacs.info) Lisp Libraries

 
 Libraries of Lisp Code for Emacs
 ================================
 
    Lisp code for Emacs editing commands is stored in files whose names
 conventionally end in `.el'.  This ending tells Emacs to edit them in
 Emacs-Lisp mode ( Executing Lisp).
 
    To execute a file of Emacs Lisp code, use `M-x load-file'.  This
 command reads a file name using the minibuffer and then executes the
 contents of that file as Lisp code.  It is not necessary to visit the
 file first; in any case, this command reads the file as found on disk,
 not text in an Emacs buffer.
 
    Once a file of Lisp code is installed in the Emacs Lisp library
 directories, users can load it using `M-x load-library'.  Programs can
 load it by calling `load-library', or with `load', a more primitive
 function that is similar but accepts some additional arguments.
 
    `M-x load-library' differs from `M-x load-file' in that it searches
 a sequence of directories and tries three file names in each directory.
 Suppose your argument is LIB; the three names are `LIB.elc', `LIB.el',
 and lastly just `LIB'.  If `LIB.elc' exists, it is by convention the
 result of compiling `LIB.el'; it is better to load the compiled file,
 since it will load and run faster.
 
    If `load-library' finds that `LIB.el' is newer than `LIB.elc' file,
 it prints a warning, because it's likely that somebody made changes to
 the `.el' file and forgot to recompile it.
 
    Because the argument to `load-library' is usually not in itself a
 valid file name, file name completion is not available.  Indeed, when
 using this command, you usually do not know exactly what file name will
 be used.
 
    The sequence of directories searched by `M-x load-library' is
 specified by the variable `load-path', a list of strings that are
 directory names.  The default value of the list contains the directory
 where the Lisp code for Emacs itself is stored.  If you have libraries
 of your own, put them in a single directory and add that directory to
 `load-path'.  `nil' in this list stands for the current default
 directory, but it is probably not a good idea to put `nil' in the list.
 If you find yourself wishing that `nil' were in the list, most likely
 what you really want to do is use `M-x load-file' this once.
 
    Often you do not have to give any command to load a library, because
 the commands defined in the library are set up to "autoload" that
 library.  Trying to run any of those commands calls `load' to load the
 library; this replaces the autoload definitions with the real ones from
 the library.
 
    Emacs Lisp code can be compiled into byte-code which loads faster,
 takes up less space when loaded, and executes faster.   Byte
 Compilation (elisp)Byte Compilation.  By convention, the compiled code
 for a library goes in a separate file whose name consists of the
 library source file with `c' appended.  Thus, the compiled code for
 `foo.el' goes in `foo.elc'.  That's why `load-library' searches for
 `.elc' files first.
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