(clim:define-application-frame application ()
  ((fat :accessor fat)
   (carbs :accessor carbs)
   (calories :accessor calories))
  (:panes
   (fat-label   (clim:make-pane 'clim:label-pane :label "Fat"))
   (carbs-label (clim:make-pane 'clim:label-pane :label "Carbs"))
   (fat-input   (clim:make-pane 'clim:text-field))
   (carbs-input (clim:make-pane 'clim:text-field))
   (calories-output (clim:make-pane 'clim:text-field))
   (button (clim:make-pane 'clim:push-button
			               :label "Calculate"
			               :activate-callback #'update-calories)))
  (:layouts
   (default
       (with-slots (fat carbs calories) clim:*application-frame*
	     (setf fat fat-input
	           carbs carbs-input
	           calories calories-output)
	     (clim:vertically (:width 300)
	       (clim:tabling ()
	         (list fat-label   fat-input)
	         (list carbs-label carbs-input))
	       button
	       calories)))))

(defun update-calories (gadget)
  (declare (ignore gadget))
  (let* ((fat (read-from-string (clim:gadget-value (fat clim:*application-frame*))))
	     (carbs (read-from-string (clim:gadget-value (carbs clim:*application-frame*))))
	     (calories (+ (* fat 9) (* carbs 4))))
    (setf (clim:gadget-value (calories clim:*application-frame*))
	      (format nil "~d calorie~:p" calories))))

(defun run-application ()
  (clim:run-frame-top-level
   (clim:make-application-frame 'application)))