Quick and dirty way to define a toggle between related files in emacs

toggle-related-files.el

(defun td-toggle-related (file to from)
  "toggles between file.from.ext and file.to.ext"
  (let ((to-from (replace-regexp-in-string to from file)) 
        (from-to (replace-regexp-in-string from to file)))
    (if (equal file to-from) from-to to-from)))

(defun td-toggle-model-view (&optional file)
  "opens related file"
  (interactive)
  (or file (setq file (buffer-name)))
  (let ((target (td-toggle-related file ".model.php" ".view.html.php")))
    (if (get-buffer target) 
	(switch-to-buffer target) 
      (find-file target))))

(defun td-toggle-model-test (&optional file)
  "opens related file"
  (interactive)
  (or file (setq file (buffer-name)))
  (let ((target (td-toggle-related file ".model.php" ".model-test.php")))
    (if (get-buffer target) 
	(switch-to-buffer target) 
      (find-file target))))

(defun td-model-view-other-window ()
 "open in a different window"
 (interactive)
 (delete-other-windows)
 (split-window)
 (td-toggle-model-view))

(defun td-model-test-other-window ()
 "open in a different window"
 (interactive)
 (delete-other-windows)
 (split-window)
 (td-toggle-model-test))


(global-set-key "\C-xr" 'td-toggle-model-view)
(global-set-key "\C-xt" 'td-toggle-model-test)

(global-set-key "\C-x5r" 'td-model-view-other-window)
(global-set-key "\C-x5t" 'td-model-test-other-window)