;; Evaluate expression to render a tree of all major modes
;; requires graphviz (http://www.graphviz.org/) to be installed

(let (tree)
  (dolist (f features)
    (require f))
  (mapatoms
   (lambda (a)
     (let ((p (get a 'derived-mode-parent)))
       (when p
	 (push (cons p a)
	       tree)))))
  (with-temp-buffer
    (insert "digraph {\n")
    (dolist (node tree)
      (insert (format "\"%s\" -> \"%s\";\n" (car node) (cdr node))))
    (insert "}\n")
    (shell-command-on-region (point-min) (point-max)
			     "dot -Tpng > dep.png")))