elisp: set-mark w/ fringe-indicator (like xyzzy)

gistfile1.el

(defvar fringe-indicator-ol nil)
(defun fringe-indicator (pt bitmap)
  (let ((s (make-string 1 ?x)))
	(when fringe-indicator-ol (delete-overlay fringe-indicator-ol))
	(setq fringe-indicator-ol (make-overlay pt (1+ pt)))
	(put-text-property 0 1 'display (list 'left-fringe bitmap) s)
	(overlay-put fringe-indicator-ol 'before-string s)))

(defadvice set-mark-command (after fringe-indicator-adv activate)
  "indicate mark-position at fringe."
  (fringe-indicator (point) 'right-triangle))