Add implementation of exercise 3-37.

Author: ramsayleung

README.org

@@ -25,7 +25,7 @@
   习题完成情况:
   - 章节一: 43/46
   - 章节二: 88/97
-  - 章节三: 36/82
+  - 章节三: 37/82
   - 章节四: TODO
   - 章节五: TODO
 * 运行

chapter3/exercise3-37.rkt

@@ -0,0 +1,82 @@
+#lang racket
+(require "constraints.rkt")
+
+;;; 有种 C++ 运算符重载的感觉了
+(define (c+ x y)
+  (let ((z (make-connector)))
+    (adder x y z)
+    z))
+
+(define (c- x y)
+  (let ((z (make-connector)))
+    ;;; x - y = z 可以转换成 x = y + z
+    (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)))
+    ;; x / y = z 可以转换成 x = y * z
+    (multiplier y z x)
+    z))
+
+(define (cv x)
+  (let ((z (make-connector)))
+    (set-value! z x 'user)
+    z))
+
+(define (celsius-fahrenheit-converter x)
+  (c+ (c* (c/ (cv 9) (cv 5))
+          x)
+      (cv 32)))
+
+(module+ test
+  (require rackunit)
+
+  (test-case "Test for c+"
+             (define a (make-connector))
+             (define b (make-connector))
+             (define sum (c+ a b))
+             (set-value! a 10 'user)
+             (set-value! b 5 'user)
+             (check-equal? (get-value sum) 15))
+
+  (test-case "Test for c-"
+             (define a (make-connector))
+             (define b (make-connector))
+             (define c (c- a b))
+             (set-value! a 10 'user)
+             (set-value! b 3 'user)
+             (check-equal? (get-value c) 7))
+
+  (test-case "Test for c*"
+             (define a (make-connector))
+             (define b (make-connector))
+             (define product (c* a b))
+             (set-value! a 10 'user)
+             (set-value! b 5 'user)
+             (check-equal? (get-value product) 50))
+
+  (test-case "Test for c/"
+             (define a (make-connector))
+             (define b (make-connector))
+             (define c (c/ a b))
+             (set-value! a 6 'user)
+             (set-value! b 2 'user)
+             (check-equal? (get-value c) 3))
+
+  (test-case "Test for cv"
+             (define c (cv 6))
+             (check-equal? (get-value c) 6))
+
+  (test-case "Test for celsius-fahrenheit-converter"
+             (define C (make-connector))
+             (define F (celsius-fahrenheit-converter C))
+             (set-value! C 25 'user)
+             (check-equal? (get-value F) 77)
+             )
+  )