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+@c -*-texinfo-*-
+@c This is part of the XEmacs Lisp Reference Manual.
+@c Copyright (C) 1990, 1991, 1992, 1993, 1994 Free Software Foundation, Inc.
+@c See the file lispref.texi for copying conditions.
+@setfilename ../../info/loading.info
+@node Loading, Byte Compilation, Macros, Top
+@chapter Loading
+@cindex loading
+@cindex library
+@cindex Lisp library
+Loading a file of Lisp code means bringing its contents into the Lisp
+environment in the form of Lisp objects.  XEmacs 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-current-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.
+@cindex 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
+@dfn{top-level 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
+definitions.
+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.
+@menu
+* How Programs Do Loading::     The @code{load} function and others.
+* 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.
+* Unloading::			How to ``unload'' a library that was loaded.
+* Hooks for Loading::		Providing code to be run when
+				  particular libraries are loaded.
+@end menu
+@node How Programs Do Loading
+@section How Programs Do Loading
+XEmacs Lisp has several interfaces for loading.  For example,
+@code{autoload} creates a placeholder object for a function 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.
+@defun load filename &optional missing-ok nomessage nosuffix
+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
+@file{@var{filename}.elc}, that is, for a file whose name is
+@var{filename} with @samp{.elc} appended.  If such a file exists, it is
+loaded.  If there is no file by that name, then @code{load} looks for a
+file named @file{@var{filename}.el}.  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 the optional argument @var{nosuffix} is non-@code{nil}, then the
+suffixes @samp{.elc} and @samp{.el} are not tried.  In this case, you
+must specify the precise file name you want.
+If @var{filename} is a relative file name, such as @file{foo} or
+@file{baz/foo.bar}, @code{load} searches for the file using the variable
+@code{load-path}.  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.
+@code{load} tries all three possible suffixes in the first directory in
+@code{load-path}, then all three suffixes in the second directory, and
+so on.
+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
+Compilation}.
+Messages like @samp{Loading foo...} and @samp{Loading foo...done} appear
+in the echo area during loading unless @var{nomessage} is
+non-@code{nil}.
+@cindex 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.
+@kindex 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
+@var{filename}}).  But if @var{missing-ok} is non-@code{nil}, then
+@code{load} 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.
+@code{load} returns @code{t} if the file loads successfully.
+@end defun
+@ignore
+@deffn Command load-file filename
+This function loads the file @var{filename}.  If @var{filename} is an
+absolute file name, then it is loaded.  If it is relative, then the
+current default directory is assumed.  @code{load-path} is not used, and
+suffixes are not appended.  Use this function if you wish to specify
+the file to be loaded exactly.
+@end deffn
+@deffn Command load-library library
+This function loads the library named @var{library}.  A library is
+nothing more than a file that may be loaded as described earlier.  This
+function is identical to @code{load}, save that it reads a file name
+interactively with completion.
+@end deffn
+@end ignore
+@defopt load-path
+@cindex @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
+directory).  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/paths.h} when XEmacs is
+built.
+The syntax of @code{EMACSLOADPATH} is the same as used for @code{PATH};
+@samp{:} (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:
+@c This overfull hbox is OK.  --rjc 16mar92
+@smallexample
+setenv EMACSLOADPATH .:/user/bil/emacs:/usr/lib/emacs/lisp
+@end smallexample
+Here is how to set it using @code{sh}:
+@smallexample
+export EMACSLOADPATH
+EMACSLOADPATH=.:/user/bil/emacs:/usr/local/lib/emacs/lisp
+@end smallexample
+Here is an example of code you can place in a @file{.emacs} file to add
+several directories to the front of your default @code{load-path}:
+@smallexample
+@group
+(setq load-path
+(append (list nil "/user/bil/emacs"
+"/usr/local/lisplib"
+"~/emacs")
+load-path))
+@end group
+@end smallexample
+@c Wordy to rid us of an overfull hbox.  --rjc 15mar92
+@noindent
+In this example, the path searches the current working directory first,
+followed then by the @file{/user/bil/emacs} directory, the
+@file{/usr/local/lisplib} directory, and the @file{~/emacs} directory,
+which are then followed by the standard directories for Lisp code.
+The command line options @samp{-l} or @samp{-load} specify a Lisp
+library to load as part of Emacs startup.  Since this file might be in
+the current directory, Emacs 18 temporarily adds the current directory
+to the front of @code{load-path} so the file can be found there.  Newer
+Emacs versions also find such files in the current directory, but
+without altering @code{load-path}.
+Dumping Emacs uses a special value of @code{load-path}.  If the value of
+@code{load-path} at the end of dumping is unchanged (that is, still the
+same special value), the dumped Emacs switches to the ordinary
+@code{load-path} value when it starts up, as described above.  But if
+@code{load-path} 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}.
+@end defopt
+@defun locate-file filename path-list &optional suffixes mode
+This function searches for a file in the same way that @code{load} does,
+and returns the file found (if any). (In fact, @code{load} uses this
+function to search through @code{load-path}.) It searches for
+@var{filename} through @var{path-list}, expanded by one of the optional
+@var{suffixes} (string of suffixes separated by @samp{:}s), checking for
+access @var{mode} (0|1|2|4 = exists|executable|writeable|readable),
+default readable.
+@code{locate-file} keeps hash tables of the directories it searches
+through, in order to speed things up.  It tries valiantly to not get
+confused in the face of a changing and unpredictable environment, but
+can occasionally get tripped up.  In this case, you will have to call
+@code{locate-file-clear-hashing} to get it back on track.  See that
+function for details.
+@end defun
+@defun locate-file-clear-hashing path
+This function clears the hash records for the specified list of
+directories.  @code{locate-file} uses a hashing scheme to speed lookup, and
+will correctly track the following environmental changes:
+@itemize @bullet
+@item
+changes of any sort to the list of directories to be searched.
+@item
+addition and deletion of non-shadowing files (see below) from the
+directories in the list.
+@item
+byte-compilation of a .el file into a .elc file.
+@end itemize
+@code{locate-file} will primarily get confused if you add a file that
+shadows (i.e. has the same name as) another file further down in the
+directory list.  In this case, you must call
+@code{locate-file-clear-hashing}.
+@end defun
+@defvar load-in-progress
+This variable is non-@code{nil} if Emacs is in the process of loading a
+file, and it is @code{nil} otherwise.
+@end defvar
+@defvar load-read-function
+This variable specifies an alternate expression-reading function for
+@code{load} 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}.
+@end defvar
+@defopt load-warn-when-source-newer
+This variable specifies whether @code{load} should check whether the
+source is newer than the binary.  If this variable is true, then when a
+@samp{.elc} file is being loaded and the corresponding @samp{.el} is
+newer, a warning message will be printed.  The default is @code{nil},
+but it is bound to @code{t} during the initial loadup.
+@end defopt
+@defopt load-warn-when-source-only
+This variable specifies whether @code{load} should warn when loading a
+@samp{.el} file instead of an @samp{.elc}.  If this variable is true,
+then when @code{load} is called with a filename without an extension,
+and the @samp{.elc} version doesn't exist but the @samp{.el} version
+does, then a message will be printed.  If an explicit extension is
+passed to @code{load}, no warning will be printed.  The default is
+@code{nil}, but it is bound to @code{t} during the initial loadup.
+@end defopt
+@defopt load-ignore-elc-files
+This variable specifies whether @code{load} should ignore @samp{.elc}
+files when a suffix is not given.  This is normally used only to
+bootstrap the @samp{.elc} files when building XEmacs, when you use the
+command @samp{make all-elc}. (This forces the @samp{.el} versions to be
+loaded in the process of compiling those same files, so that existing
+out-of-date @samp{.elc} files do not make it mess things up.)
+@end defopt
+To learn how @code{load} is used to build XEmacs, see @ref{Building XEmacs}.
+@node Autoload
+@section Autoload
+@cindex 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
+@code{autoload}, 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 do nothing on their own; they serve as a guide
+for the command @code{update-file-autoloads}, which constructs calls to
+@code{autoload} and arranges to execute them when Emacs is built.  Magic
+comments are the most convenient way to make a function autoload, but
+only for packages installed along with Emacs.
+@defun 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}.
+The argument @var{docstring} is the documentation string for the
+function.  Normally, this is the identical to the documentation string
+in the function definition itself.  Specifying the documentation string
+in the call to @code{autoload} makes it possible to look at the
+documentation without loading the function's real definition.
+If @var{interactive} is non-@code{nil}, then the function can be called
+interactively.  This lets completion in @kbd{M-x} work without loading
+the function's real definition.  The complete interactive specification
+need not be 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}.
+@cindex 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:
+@example
+(autoload @var{filename} @var{docstring} @var{interactive} @var{type})
+@end example
+For example,
+@example
+@group
+(symbol-function 'run-prolog)
+@result{} (autoload "prolog" 169681 t nil)
+@end group
+@end example
+@noindent
+In this case, @code{"prolog"} is the name of the file to load, 169681
+refers to the documentation string in the @file{emacs/etc/DOC} file
+(@pxref{Documentation Basics}), @code{t} means the function is
+interactive, and @code{nil} that it is not a macro or a keymap.
+@end defun
+@cindex 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 appear defined, but
+they might fail to work properly for the lack of certain subroutines
+defined later in the file and not loaded successfully.
+XEmacs as distributed comes with many autoloaded functions.
+The calls to @code{autoload} are in the file @file{loaddefs.el}.
+There is a convenient way of updating them automatically.
+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}"}.
+@findex update-file-autoloads
+@findex update-directory-autoloads
+A magic autoload comment looks like @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}.
+@kbd{M-x 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
+@file{loaddefs.el}.  If the form following the magic comment is not a
+function definition, it is copied verbatim.  You can also use a magic
+comment to execute a form at build time @emph{without} executing it when
+the file itself is loaded.  To do this, write the form @dfn{on the same
+line} as the magic comment.  Since it is in a comment, it does nothing
+when you load the source file; but @code{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:
+@smallexample
+;;;###autoload
+(defun doctor ()
+"Switch to *doctor* buffer and start giving psychotherapy."
+(interactive)
+(switch-to-buffer "*doctor*")
+(doctor-mode))
+@end smallexample
+@noindent
+Here's what that produces in @file{loaddefs.el}:
+@smallexample
+(autoload 'doctor "doctor"
+"\
+Switch to *doctor* buffer and start giving psychotherapy."
+t)
+@end smallexample
+@noindent
+The backslash and newline immediately following the double-quote are a
+convention used only in the preloaded Lisp files such as
+@file{loaddefs.el}; they tell @code{make-docfile} to put the
+documentation string in the @file{etc/DOC} file.  @xref{Building XEmacs}.
+@node Repeated Loading
+@section Repeated Loading
+@cindex repeated loading
+You may load one 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
+@code{load-library} 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, remember to byte-compile it if
+necessary; otherwise you may find yourself inadvertently reloading the
+older, byte-compiled file instead of your newer, non-compiled file!
+When writing the forms in a Lisp library file, keep in mind that the
+file might be loaded more than once.  For example, the choice of
+@code{defvar} vs.@: @code{defconst} for defining a variable depends on
+whether it is desirable to reinitialize the variable if the library is
+reloaded: @code{defconst} does so, and @code{defvar} does not.
+(@xref{Defining Variables}.)
+The simplest way to add an element to an alist is like this:
+@example
+(setq minor-mode-alist
+(cons '(leif-mode " Leif") minor-mode-alist))
+@end example
+@noindent
+But this would add multiple elements if the library is reloaded.
+To avoid the problem, write this:
+@example
+(or (assq 'leif-mode minor-mode-alist)
+(setq minor-mode-alist
+(cons '(leif-mode " Leif") minor-mode-alist)))
+@end example
+To add an element to a list just once, use @code{add-to-list}
+(@pxref{Setting Variables}).
+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:
+@example
+(defvar foo-was-loaded)
+(if (not (boundp 'foo-was-loaded))
+@var{execute-first-time-only})
+(setq foo-was-loaded t)
+@end example
+@noindent
+If the library uses @code{provide} to provide a named feature, you can
+use @code{featurep} to test whether the library has been loaded.
+@ifinfo
+@xref{Named Features}.
+@end ifinfo
+@node Named Features
+@section Features
+@cindex features
+@cindex requiring features
+@cindex providing features
+@code{provide} and @code{require} are an alternative to
+@code{autoload} 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
+@dfn{requiring} 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
+@code{features} 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
+@code{features}; if it fails to do so, @code{require} signals an error.
+@cindex load error with require
+Features are normally named after the files that provide them, so that
+@code{require} need not be given the file name.
+For example, in @file{emacs/lisp/prolog.el},
+the definition for @code{run-prolog} includes the following code:
+@smallexample
+(defun run-prolog ()
+"Run an inferior Prolog process, input and output via buffer *prolog*."
+(interactive)
+(require 'comint)
+(switch-to-buffer (make-comint "prolog" prolog-program-name))
+(inferior-prolog-mode))
+@end smallexample
+@noindent
+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.
+The @file{comint.el} file contains the following top-level expression:
+@smallexample
+(provide 'comint)
+@end smallexample
+@noindent
+This adds @code{comint} to the global @code{features} list, so that
+@code{(require 'comint)} will henceforth know that nothing needs to be
+done.
+@cindex 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.
+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.
+@smallexample
+@group
+(provide 'my-feature)  ; @r{Ignored by byte compiler,}
+;   @r{evaluated by @code{load}.}
+(require 'my-feature)  ; @r{Evaluated by byte compiler.}
+@end group
+@end smallexample
+@noindent
+The compiler ignores the @code{provide}, then processes the
+@code{require} by loading the file in question.  Loading the file does
+execute the @code{provide} call, so the subsequent @code{require} call
+does nothing while loading.
+@defun provide feature
+This function announces that @var{feature} is now loaded, or being
+loaded, into the current XEmacs session.  This means that the facilities
+associated with @var{feature} are or will be available for other Lisp
+programs.
+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
+@var{feature}.
+@smallexample
+features
+@result{} (bar bish)
+(provide 'foo)
+@result{} foo
+features
+@result{} (foo bar bish)
+@end smallexample
+When a file is loaded to satisfy an autoload, and it stops due to an
+error in the evaluating its contents, any function definitions or
+@code{provide} calls that occurred during the load are undone.
+@xref{Autoload}.
+@end defun
+@defun require feature &optional filename
+This function checks whether @var{feature} is present in the current
+XEmacs session (using @code{(featurep @var{feature})}; see below).  If it
+is not, 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 file name to load.
+If loading the file fails to provide @var{feature}, @code{require}
+signals an error, @samp{Required feature @var{feature} was not
+provided}.
+@end defun
+@defun featurep feature
+This function returns @code{t} if @var{feature} has been provided in the
+current XEmacs session (i.e., @var{feature} is a member of
+@code{features}.)
+@end defun
+@defvar features
+The value of this variable is a list of symbols that are the features
+loaded in the current XEmacs session.  Each symbol was put in this list
+with a call to @code{provide}.  The order of the elements in the
+@code{features} list is not significant.
+@end defvar
+@node Unloading
+@section Unloading
+@cindex unloading
+@c 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
+@code{unload-feature}:
+@deffn 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{defconst}, @code{defvar}, @code{defun},
+@code{defmacro}, @code{defsubst}, @code{definf-function} and
+@code{defalias}.  It then restores any autoloads formerly associated
+with those symbols.  (Loading saves these in the @code{autoload}
+property of the symbol.)
+Ordinarily, @code{unload-feature} refuses to unload a library on which
+other loaded libraries depend.  (A library @var{a} depends on library
+@var{b} if @var{a} contains a @code{require} for @var{b}.)  If the
+optional argument @var{force} is non-@code{nil}, dependencies are
+ignored and you can unload any library.
+@end deffn
+The @code{unload-feature} function is written in Lisp; its actions are
+based on the variable @code{load-history}.
+@defvar load-history
+This variable's value is an alist connecting library 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 name of the library, as a string.  The rest of the list is
+composed of these kinds of objects:
+@itemize @bullet
+@item
+Symbols that were defined by this library.
+@item
+Lists of the form @code{(require . @var{feature})} indicating
+features that were required.
+@item
+Lists of the form @code{(provide . @var{feature})} indicating
+features that were provided.
+@end itemize
+The value of @code{load-history} may have one element whose @sc{car} is
+@code{nil}.  This element describes definitions made with
+@code{eval-buffer} on a buffer that is not visiting a file.
+@end 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.
+@node Hooks for Loading
+@section Hooks for Loading
+@cindex loading hooks
+@cindex hooks for loading
+@ignore @c Not currently in XEmacs.  JWZ hates it.
+You can ask for code to be executed if and when a particular library is
+loaded, by calling @code{eval-after-load}.
+@defun eval-after-load library form
+This function arranges to evaluate @var{form} at the end of loading the
+library @var{library}, if and when @var{library} is loaded.  If
+@var{library} is already loaded, it evaluates @var{form} right away.
+The library name @var{library} must exactly match the argument of
+@code{load}.  To get the proper results when an installed library is
+found by searching @code{load-path}, you should not include any
+directory names in @var{library}.
+An error in @var{form} does not undo the load, but does prevent
+execution of the rest of @var{form}.
+@end 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 of programs to be
+released.
+@end ignore
+@defvar after-load-alist
+An alist of expressions to evaluate if and when particular libraries are
+loaded.  Each element looks like this:
+@example
+(@var{filename} @var{forms}@dots{})
+@end example
+When @code{load} is run and the file-name argument is @var{filename},
+the @var{forms} in the corresponding element are executed at the end of
+loading.
+@var{filename} must match exactly!  Normally @var{filename} is the name
+of a library, with no directory specified, since that is how @code{load}
+is normally called.  An error in @var{forms} does not undo the load, but
+does prevent execution of the rest of the @var{forms}.
+@ignore @c eval-after-load not in XEmacs
+The function @code{load} checks @code{after-load-alist} in order to
+implement @code{eval-after-load}.
+@end ignore
+@end defvar
+@c Emacs 19 feature

Mercurial > hg > xemacs-beta

comparison man/lispref/loading.texi @ 0:376386a54a3c r19-14