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Re: elisp programming questions

From: Barry Margolin
Subject: Re: elisp programming questions
Date: Thu, 25 Oct 2012 05:24:35 -0400
User-agent: MT-NewsWatcher/3.5.3b3 (Intel Mac OS X)

In article <address@hidden>,
 Evan Driscoll <address@hidden> wrote:

> I have a question: I'm working on a (major) mode, and when I make
> changes to the keymap, they don't "stick" until I restart emacs. It'd
> be nice to know how to fix this, but as I was typing it, I realized
> there may be a better way to solve this problem anyway; see below.
> To demo my problem:
> 1. Save the code below to a file, open in emacs
> 2. M-x eval-buffer
> 3. M-x say-hi-mode
> 4. Press [left]; note how the minibuffer says hi
>    Press [right]; note how the cursor moves
> 5. M-x revert-buffer
> 6. Uncomment the second define-key on line 8
> 7. M-x eval-buffer
> 8. Repeat steps 3 and 4. Note how [right] still
>    moves the cursor instead of saying hi
> Can someone tell me if there's a way to make the changes take effect?
> -----
> ALTERNATELY: is there some hook or something I can use which will get
> called whenever (after) the point is moved by any means? I will be
> overriding the cursor controls, but really what I want is just to
> display some stuff related to the point's new location, and ideally it'd
> work whether the user uses arrow keys, C-p/C-n/etc., the mouse, or
> anything else.
> Thanks,
> Evan
> -----
> The code:
> (defun say-hi ()
>   (interactive)
>   (message "Hello!"))
> (defvar say-hi-mode-map
>   (let ((map (make-keymap)))
>     (define-key map [left] 'say-hi)
>     ;;(define-key map [right] 'say-hi)
>     map
>     ))

DEFVAR only assigns the variable if it doesn't already have a value. So 
when you run it the second time, it doesn't do anything because the 
variable is already initialized.  Change it to:

(defvar say-hi-mode-map (make-keymap))
(define-key map [left] 'say-hi)
(define-key map [right] 'say-hi)

> (define-derived-mode say-hi-mode
>   special-mode "Trace"
>   "Major mode for viewing IO traces"
>   (use-local-map say-hi-mode-map))

Barry Margolin, address@hidden
Arlington, MA
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