It is possible for a class to have more than one parent. We can have a TA
class, a singer class, and a TA-singer class.
(define-class (singer)
(method (introduce) '(I am aiming for MTV awards!))
(method (sing) '(tralala lalala)))
(define-class (TA)
(method (introduce) '(GO BEARS!))
(method (teach) '(Let me help you with that box-and-pointer diagram)) )
(define-class (singer-TA)
(parent (singer) (TA)) )
(define-class (TA-singer)
(parent (TA) (singer)) )
> (define rohin (instantiate singer-TA))
> (define mona (instantiate TA-singer))
> (ask rohin 'introduce)
(I am aiming for MTV awards!)
> (ask rohin 'sing)
(tralala lalala)
> (ask rohin 'teach)
(Let me help you with that box-and-pointer diagram)
> (ask mona 'introduce)
(GO BEARS!)
> (ask mona 'sing)
(tralala lalala)
> (ask mona 'teach)
(Let me help you with that box-and-pointer diagram)
Note that TA-singer and singer-TA both inherit the TA class and singer
class, but in different order. When we ask instances of both class the same
message, the first parent takes precedence.
For quizzes, you may have a copy of this sheet in addition to your one-page-double-sided cheatsheet you normally have.