SICP Exercise 3.37

sicp

Question

The celsius-fahrenheit-converter procedure is cumbersome when compared with a more expression-oriented style of definition, such as

(define (celsius-fahrenheit-converter x)
  (c+ (c* (c/ (cv 9) (cv 5))
          x)
      (cv 32)))

(define C (make-connector))
(define F (celsius-fahrenheit-converter C))

Here c+, c*, etc. are the “constraint” of the arithmetic operations. For example, c+ takes two connectors as arguments and returns a connector that is related to these by an adder constraint:

(define (c+ x y)
  (let ((z (make-connector)))
    (adder x y z)
    z))

Define analogous procedures c-, c*, c/, and cv (constant value) that enable us to define compound constraints as in the converter example above.

Answer

(define (c- x y)
  (let ((z (make-connector)))
    (adder y z x)
    z))

(define (c* x y)
  (let ((z (make-connector)))
    (multiplier x y z)
    z))

(define (c/ x y)
  (let ((z (make-connector)))
    (multiplier y z x)
    z))

(define (cv x )
  (let ((y (make-connector)))
    (constant x y)
    y))