(defparameter *body* (klass (*object*) area $height volume))
(defparameter *tube* (klass (*body*) $radius))

(defmeth init *body* (u)	 
	 (setf ($height u) 1))

(defmeth area *tube* (u)
	 (* pi (expt ($radius u) 2)))

(defmeth volume *body* (u)
	 (* ($height u) (area u)))

(defmeth init *tube* (u)
	 (next u)
	 (setf ($radius u) 10))

(defun !tube ()
  (let ((tub (inst *tube*)))
    (format t "~a~%" (volume tub))
    (with-zlots tub 
      #'(lambda (prop value) 
	  (if (dollarp prop)
	      (format t "~a = ~a~%" prop value))))
    (with-vars tub
      #'(lambda (prop value)
	  (format t "~a = ~a~%" prop value)))))