411 REFERENCE · Wikibooks
The Science of Programming/SwayPresentations/Objects/ClosuresAsObjects
Reference material by Wikibooks contributors. This retains its source identity and is not 411 news reporting.
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.
Next
Previous
Top