Add test integral from the book

mceval/test-eval.rkt

@@ -45,6 +45,23 @@
       (if (= a 0) 1 b))
     (try 0 (/ 1 0))))
 
+(define lazy-integral-program
+  '((define (integral integrand initial-value dt)
+      (define int
+        (cons initial-value
+              (add-lists (scale-list integrand dt)
+                         int)))
+      int)
+    
+    (define (solve f y0 dt)
+      (define y (integral dy y0 dt))
+      (define dy (map f y))
+      y)
+
+    (define solution (solve (lambda (x) x) 1 0.001))
+    
+    (list-ref solution 1000)))
+
 (#%require rackunit)
 
 (module+ test
@@ -60,7 +77,9 @@
                 (analyzing-eval-program (fib-program 5)))
   (check-equal? (dd-eval-program (fib-program 5))
                 (lazy-eval-program (fib-program 5)))
-  (check-equal? (lazy-eval-program lazy-test-program) 1))
+  (check-equal? (lazy-eval-program lazy-test-program) 1)
+  (check-= (lazy-eval-program lazy-integral-program) 2.7169 0.01)
+  )
 
 (module+ timing
   (define dd-fib (time-proc 100 (lambda () (dd-eval-program (fib-program 10)))))