operate-on-word-at-point-or-region.el

(defun operate-on-point-or-region (fn)
  "Get the current unspaced string at point, or the current region, if selected, and replace it with the return value of fn - an ordinary defun."
  (let (pos1 pos2 meat)
    (if (and transient-mark-mode mark-active)
        (setq pos1 (region-beginning)
              pos2 (region-end))
      (setq pos1 (car (bounds-of-thing-at-point 'symbol))
            pos2 (cdr (bounds-of-thing-at-point 'symbol))))
    (setq meat (funcall fn (buffer-substring-no-properties pos1 pos2)))
    (delete-region pos1 pos2)
    (insert  meat)))