(define-class (complex real-part imag-part)
  (method (magnitude)
    (sqrt (+ (* real-part real-part)
	     (* imag-part imag-part))))
  (method (angle)
    (atan (/ imag-part real-part))) )

(define-class (counter)
  (instance-vars (count 0))
  (method (next)
    (set! count (+ count 1))
    count) )

(define-class (doubler)
  (method (say stuff) (se stuff stuff)))