Flip between js, tmpl and css files in emacs

flip-files.el

(defun open-if-exists (filename)
 (when (file-exists-p filename) (set-buffer (find-file filename)) filename))

(defun get-flipped-ext (extension)
 (cond ((string= extension "js")   "tmpl")
       ((string= extension "tmpl") "css")
       ((string= extension "css")  "js")
       (t                          nil)))

(defun try-file-flip (base extension tries)
 (let ((flipped-ext (get-flipped-ext extension)))
   (when (and (< tries 2) flipped-ext)
         (unless (open-if-exists (concat base "." flipped-ext))
           (try-file-flip base flipped-ext (+ tries 1))))))

;; Switch between [something].js -> [something].tmpl -> [something].css
(defun flip-between-viewparts ()
 (interactive)
 (let* ((file-name (buffer-file-name))
        (file-base (file-name-sans-extension file-name))
        (extension (file-name-extension file-name)))
   (try-file-flip file-base extension 0)))