Up to 3.37

constraints_propagation.rkt

@@ -161,6 +161,18 @@
 (define (connect connector new-constraint)
   ((connector 'connect) new-constraint))
 
+(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))
+
+(define (c+ x y)
+  (let ((z (make-connector)))
+    (adder x y z)
+    z))
 
 ;; 3.33
 
@@ -225,3 +237,37 @@
   (forget-value! x 'user)
   (set-value! y 81 'user)
   (check-equal? (get-value x) 9))
+
+;; 3.37
+
+(define (c- x y)
+  (let ((z (make-connector)))
+    (adder z y x)
+    z))
+
+(define (cv x)
+  (let ((z (make-connector)))
+    (constant x z)
+    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))
+
+(module+ test
+
+  (define C (make-connector))
+  (define F (celsius-fahrenheit-converter C))
+
+  (set-value! C -40 'user)
+  (check-equal? (get-value F) -40)
+
+  (forget-value! C 'user)
+  (set-value! F 212 'user)
+  (check-equal? (get-value C) 100))