Complete exercise 3.6

3_5.rkt

@@ -7,11 +7,18 @@
     (modulo (+ (* a x) b) m)))
 
 (define random-init 7)			;**not in book**
+
 (define rand
   (let ((x random-init))
-    (lambda ()
-      (set! x (rand-update x))
-      x)))
+    (lambda (arg)
+      (cond ((eq? arg 'reset)
+             (lambda (seed)
+               (set! random-init seed)))
+            ((eq? arg 'generate)
+             (set! x (rand-update x))
+             x)
+            (else
+             (error "rand - unknown argument" arg))))))
 
 (define (random-in-range low high)
   (let ((range (- high low)))