cells example

(defmodel other ()
  ((content :accessor content
	    :initarg :content
	    :initform (c-in "Test"))))

(defmodel node ()
  ((elements :accessor node-elements
             :initarg :elements
             :initform '())
   (first-element :reader first-element
		  :initform (c? (first (^node-elements))))
   (first-content-reversed :reader first-content-reversed
			   :initform (c? (reverse (content (^first-element)))))))

(defobserver first-content-reversed ((self node))
  (format t "reversed content changed: ~A~%" new-value))

(defun test-node ()
  (let* ((other (make-instance 'other))
	 (node (make-instance 'node :elements (list other))))
    (assert (string= "tseT" (first-content-reversed node)))
    (setf (content other) "Foobar")
    (assert (string= "rabooF" (first-content-reversed node)))))