(define-class (person name)
  (instance-vars (age '18))
  (method (greet)
	  (append (list 'hi 'i 'am name)   ;; NEW
		  (ask self 'sing)))        ;; NEW
  (method (sing)
	  '(cause this is thriller!)))


(define-class (rocker name)
  (parent (person name))
  (method (sing)
	  '(just a man and his will to survive!))
  (method (rocker-greet)
	  (append (ask self 'greet) '(and I am a rocker!))))


(define-class (rapper name)
  (parent (person name))
  (method (sing)
	  '(his palms are sweaty knees weak arms are heavy)))


(define-class (rocker-rapper name)
  (instance-vars (age 14))
  (parent (rocker name)
          (rapper name))
  )
  

(define bassanio (instantiate person 'bassanio))
(define antonio (instantiate rocker 'anton))
(define shylock (instantiate rapper 'shylock))
(define portia (instantiate rocker-rapper 'portia))