emacs lisp for context in AucTeX

[Sanjoy Mahajan <sanjoy@mrao.cam.ac.uk>]

I wrote the following emacs lisp for my .emacs and pass it on (no
copyright) in case others find it useful.  I used variants for a decade
with the old tex mode, but just rewrote it for auctex and for context's
display math syntax (which deprecates $$...$$).

The purpose:

1. If you type {, [, or (, the appropriate right delimiter is inserted
   for you and the insertion point is placed between them.  So I never
   get unbalanced XYZ errors.  If you think it's a misfeature, delete
   the last three local-set-key's in the TeX-mode-hook.

2. Same feature if you type $ for inline math: you get $<insertion point
   here>$.  The old tex-mode code would do the same on typing a second $,
   so you'd get $$<insertion point here>$$ for tex's display math.

   The code below will also do that, except in context mode.

3. In context mode, typing the second $ will gobble up preceding
   whitespace and then insert 
\placeformula\startformula
<place insertion point here>
\stopformula

The whitespace-deletion code in start-context-math is a bit pathetic and
any improvements are welcome.  I couldn't get re-search-backward to work
for me because it wouldn't match greedily (so it would gobble up one
space but not all of them, for example), so instead it just looks one
character at a time and deletes what it should.

-Sanjoy


(defun insert-balanced (left right)
  "Make a left, right delmiter pair and be poised to type inside of them."
  (interactive)
  (insert left)
  (save-excursion
    (insert right)))

(defun start-context-math ()
  (interactive)
  (let* ((start (max (point-min) (- (point) 1)))
	 (stop  (min (point-max) (+ (point) 1))))
    ; if in the middle of a $$, turn inline math into context display math
    (if (equal "$$" (buffer-substring-no-properties start stop))
	(progn
	  (delete-region start stop)	;get rid of the $$
	  ; delete preceding spaces, if any
	  (while (and (< (point-min) (point))
		      (equal (buffer-substring-no-properties (- (point) 1)
							     (point))
			     " "))
	    (backward-delete-char 1))
	  ; delete a preceding newline, if any
	  (if (equal (buffer-substring-no-properties (- (point) 1)
						     (point))
		     "\n")
	    (backward-delete-char 1))
	  ; place 
	  (insert "\n\\placeformula\\startformula\n")
	  (save-excursion (insert "\n\\stopformula")))
      ; else: just doing inline math
      (insert-balanced ?\$ ?\$))))

(add-hook 'ConTeXt-mode-hook
	  '(lambda ()
	     (local-set-key "$" 'start-context-math)))

(add-hook 'TeX-mode-hook
	  '(lambda ()
	     (local-set-key "$" 
			    '(lambda ()
			       (interactive)
			       (insert-balanced ?\$ ?\$)))
	     (local-set-key "{"
			    '(lambda ()
			       (interactive)
			       (insert-balanced ?\{ ?\})))
	     (local-set-key "["
			    '(lambda ()
			       (interactive)
			       (insert-balanced ?\[ ?\])))
	     (local-set-key "("
			    '(lambda ()
			       (interactive)
			       (insert-balanced ?\( ?\))))))