Last modified on 27 July 2009, at 20:15
Closures as Objects
From Structure and Interpretation of Computer Programs:
(define (account amount) (define (deposit d) (set! amount (+ amount d))) (define (withdraw w) (set! amount (- amount w))) (lambda (msg arg) (cond ((eq msg 'withdraw) (withdraw arg)) ((eq msg 'deposit) (deposit arg)) (else (error "unknown message: " msg)) ) ) )
Now we can treat account as a constructor:
(define a (account 100)) (a'withdraw 10) (a'deposit 20)
The closure that translates messages to function calls is a hack.