sicp exercise 3.37

;; Exercise 3.37.  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'' versions 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.33

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

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

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

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

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