The Science of Programming/SwayPresentations/Objects/EnvironmentsAsObjects< The Science of Programming | SwayPresentations/Objects
Environments as Objects
If you are going to use an existing 'object' as an 'Object', then environments are a better choice.
In Scheme, environments are first-class 'objects'.
(define (account amount) (define (deposit d) (set! amount (+ amount d))) (define (withdraw w) (set! amount (- amount w))) (procedure-environment (lambda () 1)) )
We need the 'dot' operator:
(define (dot obj message) (eval message obj) )
Now, our account looks like:
(define a (account 100)) ((dot a 'withdraw) 10) ((dot a 'deposit) 20)