Emacs: regular expression replacing to change case

Every once in a while I want to replace all instances of values like:

<BarFoo>

with

<barfoo>

i.e. do a regular expression replace of all things inside angle brackets with its lowercase equivalent.

Anyone got a nice snippet of Lisp that does this? It's safe to assume that we're dealing with just ASCII values. Bonus points for anything that is generic enough to take a full regular expression, and doesn't just handle the angle brackets example. Even more bonus points to an answer which just uses M-x query-replace-regexp.

Thanks,

Dom

Try M-x query-replace-regexp with "<\([^>]+\)>" as the search string and "<\,(downcase \1)>" as the replacement.

This should work for Emacs 22 and later, see this Steve Yegge blog post for more details on how Lisp expressions can be used in the replacement string.

For earlier versions of Emacs you could try something like this:

(defun tags-to-lower-case ()
  (interactive)
  (save-excursion
    (goto-char (point-min))
    (while (re-search-forward "<[^>]+>" nil t)
      (replace-match (downcase (match-string 0)) t))))