query-replace-regexp-swap ?

[Bastien]

I often come across this problem: how to swap two strings in a buffer?
For instance, say that you want to exchange #000 and #FFF in an HTML
page: all #000 should become #FFF and all #FFF should become #000.

How to do this with one *single* function ?

For now i use this:

==%<==================================================================
(defun query-replace-regexp-swap (regexp-a regexp-b beg end)
  "Swap A and B strings in the selected region."
  (interactive
   (let ((regexp-a (read-string "Regexp A: "))
         (regexp-b (read-string "Regexp B: ")))
     (list regexp-a regexp-b (region-beginning) (region-end))))
  (save-match-data
    (save-excursion
      (goto-char beg)
      (let* ((regexp (concat "\\(" regexp-a "\\)\\|"
                             "\\(" regexp-b "\\)"))
             (match-a (save-excursion
                        (re-search-forward regexp-a end t)
                        (match-string 0)))
             (match-b (save-excursion
                        (re-search-forward regexp-b end t)
                        (match-string 0))))
        (while (re-search-forward regexp nil t)
          (cond ((match-string 1) 
                 (when (y-or-n-p (format "Replace with %s? " match-b))
                                 (replace-match match-b t t)))
                ((match-string 2) 
                 (when (y-or-n-p (format "Replace with %s? " match-a))
                                 (replace-match match-a t t)))))))))
======================================================================

... which is quite UGLY.

Any idea on how to use `perform-replace' to achieve this in a more
efficient way?

-- 
Bastien