InfoMagic Source Code 1993 July/THE_SOURCE_CODE_CD_ROM.iso/languages/elisp/functions/add-hook.el

Text File | 1990-07-22 | 2.6 KB | 66 lines

;From ark1!uakari.primate.wisc.edu!brutus.cs.uiuc.edu!liberte Thu Apr 19 12:34:17 EDT 1990
;Article 1772 of comp.emacs:
;Path: ark1!uakari.primate.wisc.edu!brutus.cs.uiuc.edu!liberte
;>From: [e-mail] (Daniel LaLiberte)
;Newsgroups: comp.emacs
;Subject: Re: text-mode-hook
;Message-ID: <[e-mail]>
;Date: 15 Apr 90 22:41:10 GMT
;References: <[e-mail]> <[e-mail]>
;    <[e-mail]>
;Sender: [e-mail]
;Organization: University of Illinois, Urbana-Champaign, Dept CS
;Lines: 50
;In-reply-to: [e-mail]'s message of 12 Apr 90 03:37:48 GMT
;
;
;Here is another, more general way to solve the multiple hook problem.
;I may not have covered every case, but compared to Bob Weiner's,
;this one tests whether the hook-var already contains the hook-function;
;it also allows the hook-var to initially contain either a single function
;or a list of functions, as run-hooks supports.
;
;Now that I look at it again, I'm not even sure that it works correctly.
;But I thought I would toss it out for what it's worth.

(defun add-hook (hook-var hook-function)
  "Prepend hook-function to hook-var's value, if it is not already an element.
hook-var's value may be a single function or a list of functions."
  (if (boundp hook-var)
      (let ((value (symbol-value hook-var)))
    (if (and (listp value) (not (eq (car value) 'lambda)))
        (and (not (memq hook-function value))
         (set hook-var
              (cons hook-function value)))
      (and (not (eq hook-function value))
           (set hook-var
            (list hook-function value)))))
    (set hook-var hook-function)
    ))

;---------
;For comparison, here is the definition of run-hooks in subr.el:
;
;(defun run-hooks (&rest hooklist)
;  "Takes hook names and runs each one in turn.  Major mode functions use this.
;Each argument should be a symbol, a hook variable.
;These symbols are processed in the order specified.
;If a hook symbol has a non-nil value, that value may be a function
;or a list of functions to be called to run the hook.
;If the value is a function, it is called with no arguments.
;If it is a list, the elements are called, in order, with no arguments."
;  (while hooklist
;    (let ((sym (car hooklist)))
;      (and (boundp sym)
;       (symbol-value sym)
;       (let ((value (symbol-value sym)))
;         (if (and (listp value) (not (eq (car value) 'lambda)))
;         (mapcar 'funcall value)
;           (funcall value)))))
;    (setq hooklist (cdr hooklist))))
;
;Dan LaLiberte
;uiucdcs!liberte
;[e-mail]
;[e-mail]