Squarer as a primitive constraint
Ben Bitdiddle tells Louis that one way to avoid the trouble in exercise 3.34 is to define a squarer as a new primitive constraint. Fill in the missing portions in Ben's outline for a procedure to implement such a constraint:
(define (squarer a b) (define (process-new-value) (if (has-value? b) (if (< (get-value b) 0) (error "square less than 0 -- SQUARER" (get-value b)) <alternative1>) <alternative2>)) (define (process-forget-value) <body1>) (define (me request) <body2>) <rest of definition> me)
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