(define-application-frame puzzle ()
   ((puzzle-array :initform (make-array '(4 4))))
   (:menu-bar t)
   (:panes
     (display
       (outlining ()
         (make-pane 'application-pane
                    :text-cursor nil
                    :width :compute
                    :height :compute
                    :incremental-redisplay T
                    :display-function 'draw-puzzle))))
   (:layout
     (:default display)))

 (defmethod run-frame-top-level :before ((puzzle puzzle))
   ;; Initialize the puzzle
   ...)

 (define-presentation-type puzzle-cell ()
                           :inherit-from '(integer 1 15))

 (defmethod draw-puzzle ((puzzle puzzle) stream &key max-width max-height)
   (declare (ignore max-width max-height))
   ;; Draw the puzzle, presenting each cell as a PUZZLE-CELL
   ...)

 (define-puzzle-command com-move-cell
                        ((cell 'puzzle-cell :gesture :select))
   ;; Move the selected cell to the adjacent open cell,
   ;; if there is one
   ...)

 (define-puzzle-command (com-scramble :menu t)
                        ()
   ;; Scramble the pieces of the puzzle
   ...)

 (define-puzzle-command (com-exit-puzzle :menu "Exit")
                        ()
   (frame-exit *application-frame*))

 (defun puzzle ()
   (let ((puzzle