2015/12/03
SICP 問題 3.35
平方器を新しい基本制約として定義する.
(define (squarer a b)
(define (process-new-value)
(if (has-value? b)
(if (< (get-value b) 0)
(error "square less than 0 -- SQUARER" (get-balue b))
(set-value! a (sqrt b) me))
(set-value! b (square a) me)))
(define (process-forget-value)
(forget-value! a me)
(forget-value! b me)
(process-new-value))
(define (me request)
(cond ((eq? request 'I-have-a-value)
(process-new-value))
((eq? request 'I-lost-my-value)
(process-forget-value))
(else
(error "Unknown request -- SQUARER" request))))
me)