Info: (elisp) Hooks

elisp: Hooks

 
 22.1 Hooks
 ==========
 
 A “hook” is a variable where you can store a function or functions to be
 called on a particular occasion by an existing program.  Emacs provides
 hooks for the sake of customization.  Most often, hooks are set up in
 the init file (Init File), but Lisp programs can set them also.
 Standard Hooks, for a list of some standard hook variables.
 
    Most of the hooks in Emacs are “normal hooks”.  These variables
 contain lists of functions to be called with no arguments.  By
 convention, whenever the hook name ends in ‘-hook’, that tells you it is
 normal.  We try to make all hooks normal, as much as possible, so that
 you can use them in a uniform way.
 
    Every major mode command is supposed to run a normal hook called the
 “mode hook” as one of the last steps of initialization.  This makes it
 easy for a user to customize the behavior of the mode, by overriding the
 buffer-local variable assignments already made by the mode.  Most minor
 mode functions also run a mode hook at the end.  But hooks are used in
 other contexts too.  For example, the hook ‘suspend-hook’ runs just
 before Emacs suspends itself (Suspending Emacs).
 
    The recommended way to add a hook function to a hook is by calling
 ‘add-hook’ (Setting Hooks).  The hook functions may be any of
 the valid kinds of functions that ‘funcall’ accepts (What Is a
 Function).  Most normal hook variables are initially void; ‘add-hook’
 knows how to deal with this.  You can add hooks either globally or
 buffer-locally with ‘add-hook’.
 
    If the hook variable’s name does not end with ‘-hook’, that indicates
 it is probably an “abnormal hook”.  That means the hook functions are
 called with arguments, or their return values are used in some way.  The
 hook’s documentation says how the functions are called.  You can use
 ‘add-hook’ to add a function to an abnormal hook, but you must write the
 function to follow the hook’s calling convention.  By convention,
 abnormal hook names end in ‘-functions’.
 
    If the variable’s name ends in ‘-function’, then its value is just a
 single function, not a list of functions.  ‘add-hook’ cannot be used to
 modify such a _single function hook_, and you have to use ‘add-function’
 instead (Advising Functions).
elisp: Hooks

Menu
