Re: Idempotency of add-hook wrt lambda expressions

[M Jared Finder <jared@hpalace.com>]

Lennart Borgman wrote:
> On Wed, Mar 4, 2009 at 10:23 PM, Stefan Monnier
> <monnier@iro.umontreal.ca> wrote:
>>> if the code suggested does fix this without any other problems, why not?
>> Because it's a hack.  So it takes care of 80% of the cases but still
>> doesn't fix the remaining cases.  Fixing the remaining cases requires
>> using a symbol, so just use a symbol and get on with your life.
>> I'd much rather add a patch that complains when you pass a lambda to
>> add-hook.
> 
> Please do and do the same for menus. This would make it much easier to
> search for errors.
> 
> 
> 

I'm a user of Emacs and have created the following macro for my usage. 
I've been using it since Emacs 21.3 with no issues.  Maybe it'd be 
useful to add to Emacs?

   -- MJF

;;; Used like this:
;;;
;;; (hook-mode c-mode-common-hook
;;;   c-subword-mode
;;;  (c-set-offset 'case-label '+)
;;;  (setf (local-key-binding (kbd "C-c M-<right>"))
;;;        'c-forward-conditional
;;         (local-key-binding (kbd "C-c M-<left>"))
;;         'c-backward-conditional))

(defmacro hook-mode (hook &body modes)
   "Hook each member of MODES on HOOK.  If the member is a symbol,
call (member 1); if it is a list, just execute it directly.

This allows you to declaratively hook in minor modes on a major mode."
   (let ((body (loop for expr in modes
                     if (and (symbolp expr) (fboundp expr))
                       collect (list expr 1)
                     else if (listp expr)
                       collect expr
                     else do (error "%s does not appear to name a minor 
mode." expr))))
     `(hook-mode-attach ',hook (lambda () "Auto-generated by `hook-mode'"
                                       ,@body))))

(defvar hook-mode-*hooks* (make-hash-table :test #'eq))
(defun hook-mode-attach (hook function)
   (when (gethash hook hook-mode-*hooks*)
     (remove-hook hook (gethash hook hook-mode-*hooks*)))
   (add-hook hook function)
   (setf (gethash hook hook-mode-*hooks*) function))