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[Emacs-diffs] Changes to loading.texi

From: Glenn Morris
Subject: [Emacs-diffs] Changes to loading.texi
Date: Thu, 06 Sep 2007 04:12:28 +0000

CVSROOT:        /sources/emacs
Module name:    emacs
Changes by:     Glenn Morris <gm>       07/09/06 04:12:28

Index: loading.texi
RCS file: loading.texi
diff -N loading.texi
--- loading.texi        7 Apr 2007 01:46:44 -0000       1.74
+++ /dev/null   1 Jan 1970 00:00:00 -0000
@@ -1,968 +0,0 @@
address@hidden -*-texinfo-*-
address@hidden This is part of the GNU Emacs Lisp Reference Manual.
address@hidden Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 
address@hidden   2002, 2003, 2004, 2005, 2006, 2007  Free Software Foundation, 
address@hidden See the file elisp.texi for copying conditions.
address@hidden ../info/loading
address@hidden Loading, Byte Compilation, Customization, Top
address@hidden Loading
address@hidden loading
address@hidden library
address@hidden Lisp library
-  Loading a file of Lisp code means bringing its contents into the Lisp
-environment in the form of Lisp objects.  Emacs finds and opens the
-file, reads the text, evaluates each form, and then closes the file.
-  The load functions evaluate all the expressions in a file just
-as the @code{eval-buffer} function evaluates all the
-expressions in a buffer.  The difference is that the load functions
-read and evaluate the text in the file as found on disk, not the text
-in an Emacs buffer.
address@hidden top-level form
-  The loaded file must contain Lisp expressions, either as source code
-or as byte-compiled code.  Each form in the file is called a
address@hidden form}.  There is no special format for the forms in a
-loadable file; any form in a file may equally well be typed directly
-into a buffer and evaluated there.  (Indeed, most code is tested this
-way.)  Most often, the forms are function definitions and variable
-  A file containing Lisp code is often called a @dfn{library}.  Thus,
-the ``Rmail library'' is a file containing code for Rmail mode.
-Similarly, a ``Lisp library directory'' is a directory of files
-containing Lisp code.
-* How Programs Do Loading:: The @code{load} function and others.
-* Load Suffixes::           Details about the suffixes that @code{load} tries.
-* Library Search::          Finding a library to load.
-* Loading Non-ASCII::       address@hidden characters in Emacs Lisp files.
-* Autoload::                Setting up a function to autoload.
-* Repeated Loading::        Precautions about loading a file twice.
-* Named Features::          Loading a library if it isn't already loaded.
-* Where Defined::           Finding which file defined a certain symbol.
-* Unloading::              How to "unload" a library that was loaded.
-* Hooks for Loading::      Providing code to be run when
-                             particular libraries are loaded.
address@hidden menu
address@hidden How Programs Do Loading
address@hidden How Programs Do Loading
-  Emacs Lisp has several interfaces for loading.  For example,
address@hidden 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 (@pxref{Autoload}).  @code{require} loads a
-file if it isn't already loaded (@pxref{Named Features}).  Ultimately,
-all these facilities call the @code{load} function to do the work.
address@hidden 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, @code{load} first looks for a file named
address@hidden@var{filename}.elc}, that is, for a file whose name is
address@hidden with the extension @samp{.elc} appended.  If such a
-file exists, it is loaded.  If there is no file by that name, then
address@hidden looks for a file named @address@hidden  If that
-file exists, it is loaded.  Finally, if neither of those names is
-found, @code{load} looks for a file named @var{filename} with nothing
-appended, and loads it if it exists.  (The @code{load} function is not
-clever about looking at @var{filename}.  In the perverse case of a
-file named @file{foo.el.el}, evaluation of @code{(load "foo.el")} will
-indeed find it.)
-If Auto Compression mode is enabled, as it is by default, then if
address@hidden 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 @code{jka-compr-load-suffixes} to the file name.
-The value of this variable must be a list of strings. Its standard
-value is @code{(".gz")}.
-If the optional argument @var{nosuffix} is address@hidden, then
address@hidden does not try the suffixes @samp{.elc} and @samp{.el}.  In
-this case, you must specify the precise file name you want, except
-that, if Auto Compression mode is enabled, @code{load} will still use
address@hidden to find compressed versions.  By
-specifying the precise file name and using @code{t} for
address@hidden, you can prevent perverse file names such as
address@hidden from being tried.
-If the optional argument @var{must-suffix} is address@hidden, then
address@hidden insists that the file name used must end in either
address@hidden or @samp{.elc} (possibly extended with a compression
-suffix), unless it contains an explicit directory name.
-If @var{filename} is a relative file name, such as @file{foo} or
address@hidden/foo.bar}, @code{load} searches for the file using the variable
address@hidden  It appends @var{filename} to each of the directories
-listed in @code{load-path}, and loads the first file it finds whose name
-matches.  The current default directory is tried only if it is specified
-in @code{load-path}, where @code{nil} stands for the default directory.
address@hidden tries all three possible suffixes in the first directory in
address@hidden, then all three suffixes in the second directory, and
-so on.  @xref{Library Search}.
-If you get a warning that @file{foo.elc} is older than @file{foo.el}, it
-means you should consider recompiling @file{foo.el}.  @xref{Byte
-When loading a source file (not compiled), @code{load} performs
-character set translation just as Emacs would do when visiting the file.
address@hidden Systems}.
-Messages like @samp{Loading foo...} and @samp{Loading foo...done} appear
-in the echo area during loading unless @var{nomessage} is
address@hidden load errors
-Any unhandled errors while loading a file terminate loading.  If the
-load was done for the sake of @code{autoload}, any function definitions
-made during the loading are undone.
address@hidden file-error
-If @code{load} can't find the file to load, then normally it signals the
-error @code{file-error} (with @samp{Cannot open load file
address@hidden).  But if @var{missing-ok} is address@hidden, then
address@hidden just returns @code{nil}.
-You can use the variable @code{load-read-function} to specify a function
-for @code{load} to use instead of @code{read} for reading expressions.
-See below.
address@hidden returns @code{t} if the file loads successfully.
address@hidden defun
address@hidden Command load-file filename
-This command loads the file @var{filename}.  If @var{filename} is a
-relative file name, then the current default directory is assumed.
-This command does not use @code{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.
address@hidden deffn
address@hidden Command load-library library
-This command loads the library named @var{library}.  It is equivalent to
address@hidden, except in how it reads its argument interactively.
address@hidden deffn
address@hidden load-in-progress
-This variable is address@hidden if Emacs is in the process of loading a
-file, and it is @code{nil} otherwise.
address@hidden defvar
address@hidden load-read-function
address@hidden of load-read-function}
address@hidden do not allow page break at anchor; work around Texinfo 
-This variable specifies an alternate expression-reading function for
address@hidden and @code{eval-region} to use instead of @code{read}.
-The function should accept one argument, just as @code{read} does.
-Normally, the variable's value is @code{nil}, which means those
-functions should use @code{read}.
-Instead of using this variable, it is cleaner to use another, newer
-feature: to pass the function as the @var{read-function} argument to
address@hidden  @xref{Definition of eval-region,, Eval}.
address@hidden defvar
-  For information about how @code{load} is used in building Emacs, see
address@hidden Emacs}.
address@hidden Load Suffixes
address@hidden Load Suffixes
-We now describe some technical details about the exact suffixes that
address@hidden tries.
address@hidden load-suffixes
-This is a list of suffixes indicating (compiled or source) Emacs Lisp
-files.  It should not include the empty string.  @code{load} uses
-these suffixes in order when it appends Lisp suffixes to the specified
-file name.  The standard value is @code{(".elc" ".el")} which produces
-the behavior described in the previous section.
address@hidden defvar
address@hidden load-file-rep-suffixes
-This is a list of suffixes that indicate representations of the same
-file.  This list should normally start with the empty string.
-When @code{load} searches for a file it appends the suffixes in this
-list, in order, to the file name, before searching for another file.
-Enabling Auto Compression mode appends the suffixes in
address@hidden to this list and disabling Auto
-Compression mode removes them again.  The standard value of
address@hidden if Auto Compression mode is disabled is
address@hidden("")}.  Given that the standard value of
address@hidden is @code{(".gz")}, the standard value
-of @code{load-file-rep-suffixes} if Auto Compression mode is enabled
-is @code{("" ".gz")}.
address@hidden defvar
address@hidden get-load-suffixes
-This function returns the list of all suffixes that @code{load} should
-try, in order, when its @var{must-suffix} argument is address@hidden
-This takes both @code{load-suffixes} and @code{load-file-rep-suffixes}
-into account.  If @code{load-suffixes}, @code{jka-compr-load-suffixes}
-and @code{load-file-rep-suffixes} all have their standard values, this
-function returns @code{(".elc" ".elc.gz" ".el" ".el.gz")} if Auto
-Compression mode is enabled and @code{(".elc" ".el")} if Auto
-Compression mode is disabled.
address@hidden defun
-To summarize, @code{load} normally first tries the suffixes in the
-value of @code{(get-load-suffixes)} and then those in
address@hidden  If @var{nosuffix} is address@hidden,
-it skips the former group, and if @var{must-suffix} is address@hidden,
-it skips the latter group.
address@hidden Library Search
address@hidden Library Search
address@hidden library search
address@hidden find library
-  When Emacs loads a Lisp library, it searches for the library
-in a list of directories specified by the variable @code{load-path}.
address@hidden load-path
address@hidden @code{EMACSLOADPATH} environment variable
-The value of this variable is a list of directories to search when
-loading files with @code{load}.  Each element is a string (which must be
-a directory name) or @code{nil} (which stands for the current working
address@hidden defopt
-  The value of @code{load-path} is initialized from the environment
-variable @code{EMACSLOADPATH}, if that exists; otherwise its default
-value is specified in @file{emacs/src/epaths.h} when Emacs is built.
-Then the list is expanded by adding subdirectories of the directories
-in the list.
-  The syntax of @code{EMACSLOADPATH} is the same as used for @code{PATH};
address@hidden:} (or @samp{;}, according to the operating system) separates
-directory names, and @samp{.} is used for the current default directory.
-Here is an example of how to set your @code{EMACSLOADPATH} variable from
-a @code{csh} @file{.login} file:
-setenv EMACSLOADPATH .:/user/bil/emacs:/usr/local/share/emacs/20.3/lisp
address@hidden smallexample
-  Here is how to set it using @code{sh}:
address@hidden smallexample
-  Here is an example of code you can place in your init file (@pxref{Init
-File}) to add several directories to the front of your default
-(setq load-path
-      (append (list nil "/user/bil/emacs"
-                    "/usr/local/lisplib"
-                    "~/emacs")
-              load-path))
address@hidden group
address@hidden smallexample
address@hidden Wordy to rid us of an overfull hbox.  --rjc 15mar92
-In this example, the path searches the current working directory first,
-followed then by the @file{/user/bil/emacs} directory, the
address@hidden/usr/local/lisplib} directory, and the @file{~/emacs} directory,
-which are then followed by the standard directories for Lisp code.
-  Dumping Emacs uses a special value of @code{load-path}.  If the value of
address@hidden at the end of dumping is unchanged (that is, still the
-same special value), the dumped Emacs switches to the ordinary
address@hidden value when it starts up, as described above.  But if
address@hidden has any other value at the end of dumping, that value
-is used for execution of the dumped Emacs also.
-  Therefore, if you want to change @code{load-path} temporarily for
-loading a few libraries in @file{site-init.el} or @file{site-load.el},
-you should bind @code{load-path} locally with @code{let} around the
-calls to @code{load}.
-  The default value of @code{load-path}, when running an Emacs which has
-been installed on the system, includes two special directories (and
-their subdirectories as well):
address@hidden smallexample
address@hidden smallexample
-The first one is for locally installed packages for a particular Emacs
-version; the second is for locally installed packages meant for use with
-all installed Emacs versions.
-  There are several reasons why a Lisp package that works well in one
-Emacs version can cause trouble in another.  Sometimes packages need
-updating for incompatible changes in Emacs; sometimes they depend on
-undocumented internal Emacs data that can change without notice;
-sometimes a newer Emacs version incorporates a version of the package,
-and should be used only with that version.
-  Emacs finds these directories' subdirectories and adds them to
address@hidden when it starts up.  Both immediate subdirectories and
-subdirectories multiple levels down are added to @code{load-path}.
-  Not all subdirectories are included, though.  Subdirectories whose
-names do not start with a letter or digit are excluded.  Subdirectories
-named @file{RCS} or @file{CVS} are excluded.  Also, a subdirectory which
-contains a file named @file{.nosearch} is excluded.  You can use these
-methods to prevent certain subdirectories of the @file{site-lisp}
-directories from being searched.
-  If you run Emacs from the directory where it was built---that is, an
-executable that has not been formally installed---then @code{load-path}
-normally contains two additional directories.  These are the @code{lisp}
-and @code{site-lisp} subdirectories of the main build directory.  (Both
-are represented as absolute file names.)
address@hidden Command locate-library library &optional nosuffix path 
-This command finds the precise file name for library @var{library}.  It
-searches for the library in the same way @code{load} does, and the
-argument @var{nosuffix} has the same meaning as in @code{load}: don't
-add suffixes @samp{.elc} or @samp{.el} to the specified name
-If the @var{path} is address@hidden, that list of directories is used
-instead of @code{load-path}.
-When @code{locate-library} is called from a program, it returns the file
-name as a string.  When the user runs @code{locate-library}
-interactively, the argument @var{interactive-call} is @code{t}, and this
-tells @code{locate-library} to display the file name in the echo area.
address@hidden deffn
address@hidden Loading Non-ASCII
address@hidden Loading address@hidden Characters
-  When Emacs Lisp programs contain string constants with address@hidden
-characters, these can be represented within Emacs either as unibyte
-strings or as multibyte strings (@pxref{Text Representations}).  Which
-representation is used depends on how the file is read into Emacs.  If
-it is read with decoding into multibyte representation, the text of the
-Lisp program will be multibyte text, and its string constants will be
-multibyte strings.  If a file containing Latin-1 characters (for
-example) is read without decoding, the text of the program will be
-unibyte text, and its string constants will be unibyte strings.
address@hidden Systems}.
-  To make the results more predictable, Emacs always performs decoding
-into the multibyte representation when loading Lisp files, even if it
-was started with the @samp{--unibyte} option.  This means that string
-constants with address@hidden characters translate into multibyte
-strings.  The only exception is when a particular file specifies no
-  The reason Emacs is designed this way is so that Lisp programs give
-predictable results, regardless of how Emacs was started.  In addition,
-this enables programs that depend on using multibyte text to work even
-in a unibyte Emacs.  Of course, such programs should be designed to
-notice whether the user prefers unibyte or multibyte text, by checking
address@hidden, and convert representations
-  In most Emacs Lisp programs, the fact that address@hidden strings are
-multibyte strings should not be noticeable, since inserting them in
-unibyte buffers converts them to unibyte automatically.  However, if
-this does make a difference, you can force a particular Lisp file to be
-interpreted as unibyte by writing @samp{-*-unibyte: t;-*-} in a
-comment on the file's first line.  With that designator, the file will
-unconditionally be interpreted as unibyte, even in an ordinary
-multibyte Emacs session.  This can matter when making keybindings to
address@hidden characters written as @address@hidden
address@hidden Autoload
address@hidden Autoload
address@hidden autoload
-  The @dfn{autoload} facility allows you to make a function or macro
-known in Lisp, but put off loading the file that defines it.  The first
-call to the function automatically reads the proper file to install the
-real definition and other associated code, then runs the real definition
-as if it had been loaded all along.
-  There are two ways to set up an autoloaded function: by calling
address@hidden, and by writing a special ``magic'' comment in the
-source before the real definition.  @code{autoload} is the low-level
-primitive for autoloading; any Lisp program can call @code{autoload} at
-any time.  Magic comments are the most convenient way to make a function
-autoload, for packages installed along with Emacs.  These comments do
-nothing on their own, but they serve as a guide for the command
address@hidden, which constructs calls to @code{autoload}
-and arranges to execute them when Emacs is built.
address@hidden autoload function filename &optional docstring interactive type
-This function defines the function (or macro) named @var{function} so as
-to load automatically from @var{filename}.  The string @var{filename}
-specifies the file to load to get the real definition of @var{function}.
-If @var{filename} does not contain either a directory name, or the
-suffix @code{.el} or @code{.elc}, then @code{autoload} insists on adding
-one of these suffixes, and it will not load from a file whose name is
-just @var{filename} with no added suffix.  (The variable
address@hidden specifies the exact required suffixes.)
-The argument @var{docstring} is the documentation string for the
-function.  Specifying the documentation string in the call to
address@hidden makes it possible to look at the documentation without
-loading the function's real definition.  Normally, this should be
-identical to the documentation string in the function definition
-itself.  If it isn't, the function definition's documentation string
-takes effect when it is loaded.
-If @var{interactive} is address@hidden, that says @var{function} can be
-called interactively.  This lets completion in @kbd{M-x} work without
-loading @var{function}'s real definition.  The complete interactive
-specification is not given here; it's not needed unless the user
-actually calls @var{function}, and when that happens, it's time to load
-the real definition.
-You can autoload macros and keymaps as well as ordinary functions.
-Specify @var{type} as @code{macro} if @var{function} is really a macro.
-Specify @var{type} as @code{keymap} if @var{function} is really a
-keymap.  Various parts of Emacs need to know this information without
-loading the real definition.
-An autoloaded keymap loads automatically during key lookup when a prefix
-key's binding is the symbol @var{function}.  Autoloading does not occur
-for other kinds of access to the keymap.  In particular, it does not
-happen when a Lisp program gets the keymap from the value of a variable
-and calls @code{define-key}; not even if the variable name is the same
-symbol @var{function}.
address@hidden function cell in autoload
-If @var{function} already has a non-void function definition that is not
-an autoload object, @code{autoload} does nothing and returns @code{nil}.
-If the function cell of @var{function} is void, or is already an autoload
-object, then it is defined as an autoload object like this:
-(autoload @var{filename} @var{docstring} @var{interactive} @var{type})
address@hidden example
-For example,
-(symbol-function 'run-prolog)
-     @result{} (autoload "prolog" 169681 t nil)
address@hidden group
address@hidden example
-In this case, @code{"prolog"} is the name of the file to load, 169681
-refers to the documentation string in the
address@hidden/etc/address@hidden file (@pxref{Documentation Basics}),
address@hidden means the function is interactive, and @code{nil} that it is
-not a macro or a keymap.
address@hidden defun
address@hidden autoload errors
-  The autoloaded file usually contains other definitions and may require
-or provide one or more features.  If the file is not completely loaded
-(due to an error in the evaluation of its contents), any function
-definitions or @code{provide} calls that occurred during the load are
-undone.  This is to ensure that the next attempt to call any function
-autoloading from this file will try again to load the file.  If not for
-this, then some of the functions in the file might be defined by the
-aborted load, but fail to work properly for the lack of certain
-subroutines not loaded successfully because they come later in the file.
-  If the autoloaded file fails to define the desired Lisp function or
-macro, then an error is signaled with data @code{"Autoloading failed to
-define function @var{function-name}"}.
address@hidden update-file-autoloads
address@hidden update-directory-autoloads
address@hidden magic autoload comment
address@hidden autoload cookie
address@hidden cookie}
-  A magic autoload comment (often called an @dfn{autoload cookie})
-consists of @samp{;;;###autoload}, on a line by itself,
-just before the real definition of the function in its
-autoloadable source file.  The command @kbd{M-x update-file-autoloads}
-writes a corresponding @code{autoload} call into @file{loaddefs.el}.
-Building Emacs loads @file{loaddefs.el} and thus calls @code{autoload}.
address@hidden update-directory-autoloads} is even more powerful; it updates
-autoloads for all files in the current directory.
-  The same magic comment can copy any kind of form into
address@hidden  If the form following the magic comment is not a
-function-defining form or a @code{defcustom} form, it is copied
-verbatim.  ``Function-defining forms'' include @code{define-skeleton},
address@hidden, @code{define-generic-mode} and
address@hidden as well as @code{defun} and
address@hidden  To save space, a @code{defcustom} form is converted to
-a @code{defvar} in @file{loaddefs.el}, with some additional information
-if it uses @code{:require}.
-  You can also use a magic comment to execute a form at build time
address@hidden executing it when the file itself is loaded.  To do this,
-write the form @emph{on the same line} as the magic comment.  Since it
-is in a comment, it does nothing when you load the source file; but
address@hidden update-file-autoloads} copies it to @file{loaddefs.el}, where
-it is executed while building Emacs.
-  The following example shows how @code{doctor} is prepared for
-autoloading with a magic comment:
-(defun doctor ()
-  "Switch to *doctor* buffer and start giving psychotherapy."
-  (interactive)
-  (switch-to-buffer "*doctor*")
-  (doctor-mode))
address@hidden smallexample
-Here's what that produces in @file{loaddefs.el}:
-(autoload (quote doctor) "doctor" "\
-Switch to *doctor* buffer and start giving psychotherapy.
-\(fn)" t nil)
address@hidden smallexample
address@hidden @code{fn} in function's documentation string
-The backslash and newline immediately following the double-quote are a
-convention used only in the preloaded uncompiled Lisp files such as
address@hidden; they tell @code{make-docfile} to put the
-documentation string in the @file{etc/DOC} file.  @xref{Building Emacs}.
-See also the commentary in @file{lib-src/make-docfile.c}.  @samp{(fn)}
-in the usage part of the documentation string is replaced with the
-function's name when the various help functions (@pxref{Help
-Functions}) display it.
-  If you write a function definition with an unusual macro that is not
-one of the known and recognized function definition methods, use of an
-ordinary magic autoload comment would copy the whole definition into
address@hidden  That is not desirable.  You can put the desired
address@hidden call into @code{loaddefs.el} instead by writing this:
-;;;###autoload (autoload 'foo "myfile")
-(mydefunmacro foo
-  ...)
address@hidden smallexample
address@hidden Repeated Loading
address@hidden Repeated Loading
address@hidden repeated loading
-  You can load a given file more than once in an Emacs session.  For
-example, after you have rewritten and reinstalled a function definition
-by editing it in a buffer, you may wish to return to the original
-version; you can do this by reloading the file it came from.
-  When you load or reload files, bear in mind that the @code{load} and
address@hidden functions automatically load a byte-compiled file
-rather than a non-compiled file of similar name.  If you rewrite a file
-that you intend to save and reinstall, you need to byte-compile the new
-version; otherwise Emacs will load the older, byte-compiled file instead
-of your newer, non-compiled file!  If that happens, the message
-displayed when loading the file includes, @samp{(compiled; note, source is
-newer)}, to remind you to recompile it.
-  When writing the forms in a Lisp library file, keep in mind that the
-file might be loaded more than once.  For example, think about whether
-each variable should be reinitialized when you reload the library;
address@hidden does not change the value if the variable is already
-initialized.  (@xref{Defining Variables}.)
-  The simplest way to add an element to an alist is like this:
-(push '(leif-mode " Leif") minor-mode-alist)
address@hidden example
-But this would add multiple elements if the library is reloaded.
-To avoid the problem, write this:
-(or (assq 'leif-mode minor-mode-alist)
-    (push '(leif-mode " Leif") minor-mode-alist))
address@hidden example
-or this:
-(add-to-list '(leif-mode " Leif") minor-mode-alist)
address@hidden example
-  Occasionally you will want to test explicitly whether a library has
-already been loaded.  Here's one way to test, in a library, whether it
-has been loaded before:
-(defvar foo-was-loaded nil)
-(unless foo-was-loaded
-  @var{execute-first-time-only}
-  (setq foo-was-loaded t))
address@hidden example
-If the library uses @code{provide} to provide a named feature, you can
-use @code{featurep} earlier in the file to test whether the
address@hidden call has been executed before.
address@hidden Features}.
address@hidden ifnottex
address@hidden Named Features
address@hidden Features
address@hidden features
address@hidden requiring features
address@hidden providing features
-  @code{provide} and @code{require} are an alternative to
address@hidden for loading files automatically.  They work in terms of
-named @dfn{features}.  Autoloading is triggered by calling a specific
-function, but a feature is loaded the first time another program asks
-for it by name.
-  A feature name is a symbol that stands for a collection of functions,
-variables, etc.  The file that defines them should @dfn{provide} the
-feature.  Another program that uses them may ensure they are defined by
address@hidden the feature.  This loads the file of definitions if it
-hasn't been loaded already.
-  To require the presence of a feature, call @code{require} with the
-feature name as argument.  @code{require} looks in the global variable
address@hidden to see whether the desired feature has been provided
-already.  If not, it loads the feature from the appropriate file.  This
-file should call @code{provide} at the top level to add the feature to
address@hidden; if it fails to do so, @code{require} signals an error.
address@hidden load error with require
-  For example, in @file{emacs/lisp/prolog.el},
-the definition for @code{run-prolog} includes the following code:
-(defun run-prolog ()
-  "Run an inferior Prolog process, with I/O via buffer *prolog*."
-  (interactive)
-  (require 'comint)
-  (switch-to-buffer (make-comint "prolog" prolog-program-name))
-  (inferior-prolog-mode))
address@hidden smallexample
-The expression @code{(require 'comint)} loads the file @file{comint.el}
-if it has not yet been loaded.  This ensures that @code{make-comint} is
-defined.  Features are normally named after the files that provide them,
-so that @code{require} need not be given the file name.
-The @file{comint.el} file contains the following top-level expression:
-(provide 'comint)
address@hidden smallexample
-This adds @code{comint} to the global @code{features} list, so that
address@hidden(require 'comint)} will henceforth know that nothing needs to be
address@hidden byte-compiling @code{require}
-  When @code{require} is used at top level in a file, it takes effect
-when you byte-compile that file (@pxref{Byte Compilation}) as well as
-when you load it.  This is in case the required package contains macros
-that the byte compiler must know about.  It also avoids byte-compiler
-warnings for functions and variables defined in the file loaded with
-  Although top-level calls to @code{require} are evaluated during
-byte compilation, @code{provide} calls are not.  Therefore, you can
-ensure that a file of definitions is loaded before it is byte-compiled
-by including a @code{provide} followed by a @code{require} for the same
-feature, as in the following example.
-(provide 'my-feature)  ; @r{Ignored by byte compiler,}
-                       ;   @r{evaluated by @code{load}.}
-(require 'my-feature)  ; @r{Evaluated by byte compiler.}
address@hidden group
address@hidden smallexample
-The compiler ignores the @code{provide}, then processes the
address@hidden by loading the file in question.  Loading the file does
-execute the @code{provide} call, so the subsequent @code{require} call
-does nothing when the file is loaded.
address@hidden provide feature &optional subfeatures
-This function announces that @var{feature} is now loaded, or being
-loaded, into the current Emacs session.  This means that the facilities
-associated with @var{feature} are or will be available for other Lisp
-The direct effect of calling @code{provide} is to add @var{feature} to
-the front of the list @code{features} if it is not already in the list.
-The argument @var{feature} must be a symbol.  @code{provide} returns
-If provided, @var{subfeatures} should be a list of symbols indicating
-a set of specific subfeatures provided by this version of
address@hidden  You can test the presence of a subfeature using
address@hidden  The idea of subfeatures is that you use them when a
-package (which is one @var{feature}) is complex enough to make it
-useful to give names to various parts or functionalities of the
-package, which might or might not be loaded, or might or might not be
-present in a given version.  @xref{Network Feature Testing}, for
-an example.
-     @result{} (bar bish)
-(provide 'foo)
-     @result{} foo
-     @result{} (foo bar bish)
address@hidden smallexample
-When a file is loaded to satisfy an autoload, and it stops due to an
-error in the evaluation of its contents, any function definitions or
address@hidden calls that occurred during the load are undone.
address@hidden defun
address@hidden require feature &optional filename noerror
-This function checks whether @var{feature} is present in the current
-Emacs session (using @code{(featurep @var{feature})}; see below).  The
-argument @var{feature} must be a symbol.
-If the feature is not present, then @code{require} loads @var{filename}
-with @code{load}.  If @var{filename} is not supplied, then the name of
-the symbol @var{feature} is used as the base file name to load.
-However, in this case, @code{require} insists on finding @var{feature}
-with an added @samp{.el} or @samp{.elc} suffix (possibly extended with
-a compression suffix); a file whose name is just @var{feature} won't
-be used.  (The variable @code{load-suffixes} specifies the exact
-required Lisp suffixes.)
-If @var{noerror} is address@hidden, that suppresses errors from actual
-loading of the file.  In that case, @code{require} returns @code{nil}
-if loading the file fails.  Normally, @code{require} returns
-If loading the file succeeds but does not provide @var{feature},
address@hidden signals an error, @samp{Required feature @var{feature}
-was not provided}.
address@hidden defun
address@hidden featurep feature &optional subfeature
-This function returns @code{t} if @var{feature} has been provided in
-the current Emacs session (i.e.@:, if @var{feature} is a member of
address@hidden)  If @var{subfeature} is address@hidden, then the
-function returns @code{t} only if that subfeature is provided as well
-(i.e.@: if @var{subfeature} is a member of the @code{subfeature}
-property of the @var{feature} symbol.)
address@hidden defun
address@hidden features
-The value of this variable is a list of symbols that are the features
-loaded in the current Emacs session.  Each symbol was put in this list
-with a call to @code{provide}.  The order of the elements in the
address@hidden list is not significant.
address@hidden defvar
address@hidden Where Defined
address@hidden Which File Defined a Certain Symbol
address@hidden symbol-file symbol &optional type
-This function returns the name of the file that defined @var{symbol}.
-If @var{type} is @code{nil}, then any kind of definition is
-acceptable.  If @var{type} is @code{defun} or @code{defvar}, that
-specifies function definition only or variable definition only.
-The value is normally an absolute file name.  It can also be
address@hidden, if the definition is not associated with any file.
address@hidden defun
-  The basis for @code{symbol-file} is the data in the variable
address@hidden load-history
-This variable's value is an alist connecting library file names with the
-names of functions and variables they define, the features they provide,
-and the features they require.
-Each element is a list and describes one library.  The @sc{car} of the
-list is the absolute file name of the library, as a string.  The rest
-of the list elements have these forms:
address@hidden @code
address@hidden @var{var}
-The symbol @var{var} was defined as a variable.
address@hidden (defun . @var{fun})
-The function @var{fun} was defined.
address@hidden (t . @var{fun})
-The function @var{fun} was previously an autoload before this library
-redefined it as a function.  The following element is always
address@hidden(defun . @var{fun})}, which represents defining @var{fun} as a
address@hidden (autoload . @var{fun})
-The function @var{fun} was defined as an autoload.
address@hidden (require . @var{feature})
-The feature @var{feature} was required.
address@hidden (provide . @var{feature})
-The feature @var{feature} was provided.
address@hidden table
-The value of @code{load-history} may have one element whose @sc{car} is
address@hidden  This element describes definitions made with
address@hidden on a buffer that is not visiting a file.
address@hidden defvar
-  The command @code{eval-region} updates @code{load-history}, but does so
-by adding the symbols defined to the element for the file being visited,
-rather than replacing that element.  @xref{Eval}.
address@hidden Unloading
address@hidden Unloading
address@hidden unloading packages
address@hidden Emacs 19 feature
-  You can discard the functions and variables loaded by a library to
-reclaim memory for other Lisp objects.  To do this, use the function
address@hidden Command unload-feature feature &optional force
-This command unloads the library that provided feature @var{feature}.
-It undefines all functions, macros, and variables defined in that
-library with @code{defun}, @code{defalias}, @code{defsubst},
address@hidden, @code{defconst}, @code{defvar}, and @code{defcustom}.
-It then restores any autoloads formerly associated with those symbols.
-(Loading saves these in the @code{autoload} property of the symbol.)
address@hidden unload-feature-special-hooks
-Before restoring the previous definitions, @code{unload-feature} runs
address@hidden to remove functions in the library from certain
-hooks.  These hooks include variables whose names end in @samp{hook}
-or @samp{-hooks}, plus those listed in
address@hidden  This is to prevent Emacs from
-ceasing to function because important hooks refer to functions that
-are no longer defined.
address@hidden @var{feature}-unload-hook
-If these measures are not sufficient to prevent malfunction, a library
-can define an explicit unload hook.  If @address@hidden
-is defined, it is run as a normal hook before restoring the previous
-definitions, @emph{instead of} the usual hook-removing actions.  The
-unload hook ought to undo all the global state changes made by the
-library that might cease to work once the library is unloaded.
address@hidden can cause problems with libraries that fail to do
-this, so it should be used with caution.
-Ordinarily, @code{unload-feature} refuses to unload a library on which
-other loaded libraries depend.  (A library @var{a} depends on library
address@hidden if @var{a} contains a @code{require} for @var{b}.)  If the
-optional argument @var{force} is address@hidden, dependencies are
-ignored and you can unload any library.
address@hidden deffn
-  The @code{unload-feature} function is written in Lisp; its actions are
-based on the variable @code{load-history}.
address@hidden unload-feature-special-hooks
-This variable holds a list of hooks to be scanned before unloading a
-library, to remove functions defined in the library.
address@hidden defvar
address@hidden Hooks for Loading
address@hidden Hooks for Loading
address@hidden loading hooks
address@hidden hooks for loading
-You can ask for code to be executed if and when a particular library is
-loaded, by calling @code{eval-after-load}.
address@hidden eval-after-load library form
-This function arranges to evaluate @var{form} at the end of loading
-the file @var{library}, each time @var{library} is loaded.  If
address@hidden is already loaded, it evaluates @var{form} right away.
-Don't forget to quote @var{form}!
-You don't need to give a directory or extension in the file name
address@hidden you just give a bare file name, like this:
-(eval-after-load "edebug" '(def-edebug-spec c-point t))
address@hidden example
-To restrict which files can trigger the evaluation, include a
-directory or an extension or both in @var{library}.  Only a file whose
-absolute true name (i.e., the name with all symbolic links chased out)
-matches all the given name components will match.  In the following
-example, @file{my_inst.elc} or @file{my_inst.elc.gz} in some directory
address@hidden/foo/bar} will trigger the evaluation, but not
-(eval-after-load "foo/bar/my_inst.elc" @dots{})
address@hidden example
address@hidden can also be a feature (i.e.@: a symbol), in which case
address@hidden is evaluated when @code{(provide @var{library})} is called.
-An error in @var{form} does not undo the load, but does prevent
-execution of the rest of @var{form}.
address@hidden defun
-In general, well-designed Lisp programs should not use this feature.
-The clean and modular ways to interact with a Lisp library are (1)
-examine and set the library's variables (those which are meant for
-outside use), and (2) call the library's functions.  If you wish to
-do (1), you can do it immediately---there is no need to wait for when
-the library is loaded.  To do (2), you must load the library (preferably
-with @code{require}).
-But it is OK to use @code{eval-after-load} in your personal
-customizations if you don't feel they must meet the design standards for
-programs meant for wider use.
address@hidden after-load-alist
-This variable, an alist built by @code{eval-after-load}, holds the
-expressions to evaluate when particular libraries are loaded.  Each
-element looks like this:
-(@var{regexp-or-feature} @address@hidden)
address@hidden example
-The key @var{regexp-or-feature} is either a regular expression or a
-symbol, and the value is a list of forms.  The forms are evaluated when
-the key matches the absolute true name of the file being
address@hidden or the symbol being @code{provide}d.
address@hidden defvar
-   arch-tag: df731f89-0900-4389-a436-9105241b6f7a
address@hidden ignore

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