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From: Lars Magne Ingebrigtsen <larsi@ifi.uio.no>
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Subject: Re: September Gnus 0.60 is released
Date: 02 Apr 1996 22:01:55 +0200
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Hallvard B Furuseth <h.b.furuseth@usit.uio.no> writes:

> Should the hook be called:
> * every time (user-mail-address) is called (i.e. a hook to the
>   (user-mail-addres) *function*), or
> * just the first time user-mail-address is computed (i.e.  a hook to the
>   user-mail-addres *variable*)?

I think it should probably be called just the first time the address
is computed.  The point of this was that sometimes it can be rather
much work to get to the official mail address, so doing it more than
once is probably counterproductive.

Now -- the `user-mail-address' has to have a default string value.
The `user-mail-address' function should call the hook to alter the
`user-mail-address' function *unless* it has been changed by the
user.  

So how about doing something like this:

;; default.el
(defvar user-mail-address 
   (let ((address (concat (user-login-name) "@" (system-name))))
     (put-text-property 0 1 'user-address-function 'get-official-address
                        address)
     address))

(defun user-mail-address ()
  (let ((func (get-text-property 0 1 'user-address-function 
                                 user-mail-address)))
    (when func (funcall func)))
  user-mail-address)

(defun get-official-address ()
  (setq user-mail-address (whatever ...)))

Kludgy as hell, but this should ensure that `get-official-address' is
called once only, and that it is never called if the user sets
`user-mail-address' in her .emacs file.

-- 
  "Yes.  The journey through the human heart 
     would have to wait until some other time."