(add-to-list 'auto-mode-alist '("\\.md$" . markdown-mode))

(setq ditaa-cmd "ditaa")
(defun ditaa-generate (start end)
  (interactive "r")
  (let ((tmpfile (make-temp-file "ditaa")))
    (write-region start end tmpfile)
    (shell-command
     (concat ditaa-cmd " " tmpfile " " (concat buffer-file-name ".png")))))

(provide 'my-markdown)