Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!usc!orion.oac.uci.edu!ucivax!megatek!hollen
From: hollen@megatek (Dion Hollenbeck)
Newsgroups: comp.emacs
Subject: Re: toggling key definitions
Message-ID: <HOLLEN.90Nov29073252@fridge.megatek>
Date: 29 Nov 90 15:32:52 GMT
References: <9322@ncar.ucar.edu>
Sender: news@megatek.UUCP
Organization: Megatek Corporation, San Diego, California
Lines: 44
In-reply-to: southern@neit.cgd.ucar.edu's message of 28 Nov 90 19:32:39 GMT

In article <9322@ncar.ucar.edu> southern@neit.cgd.ucar.edu writes:
>
>  I would like to use only one key to toggle between the start-kbd-macro
>  and end-kbd-macro commands such that:
>   if I currently am not defining a keyboard macro, 7 maps to start-kbd-macro 
>   if I currently am     defining a keyboard macro, 7 maps to end-kbd-macro.
> 

Someone suggested a way to do this which required that inside the
function which is REALLY bound to the key, test the state of something
and then call the appropriate function.  Like this:

(defun toggle-kbd-macro ()
  "Start or end a keyboard macro."
  (if defining-kbd-macro
      (end-kbd-macro)
    (start-kbd-macro)))

This is fine when one has some sort of variable to test, but may
be difficult to implement in some cases.  I propose a more generic
method which will work in all cases regardless of whether variables
are present to be tested.  It also does not require such variables
to be created if not used for any other purposes.  The mere act
of calling a function indicates the state and from there, that
function knows the next state which should be set up.

(define-key function-keymap "7" 'my-start-kbd-macro)   ; "7"

(defun my-start-kbd-macro ()
	"Start keyboard macro and change key state."
	(define-key function-keymap "7" 'my-end-kbd-macro)   ; "7"
	(start-kbd-macro))

(defun my-end-kbd-macro ()
	"Start keyboard macro and change key state."
	(define-key function-keymap "7" 'my-start-kbd-macro)   ; "7"
	(end-kbd-macro))

This is used in edt.el to handle the ADVANCE/BACKUP keys.  You can 
look at the code there for more explicit examples if you need.
--
	Dion Hollenbeck             (619) 455-5590 x2814
	Megatek Corporation, 9645 Scranton Road, San Diego, CA  92121
        uunet!megatek!hollen       or  hollen@megatek.uucp