solution to 4.31

[sicp.git] / src / sicp / streams.rkt

diff --git a/src/sicp/streams.rkt b/src/sicp/streams.rkt
index b68afe1ff0636c15a75de12e8d9192f788dadc9f..b0540aedb1246cec7e517dd7bc2401a477704ccb 100644 (file)
--- a/src/sicp/streams.rkt
+++ b/src/sicp/streams.rkt
@@ -1,5 +1,7 @@
 #lang planet neil/sicp
 
+(#%require (only racket random))
+
 (define (stream-car s) (car s))
 (define (stream-cdr s) (force (cdr s)))
 
@@ -120,4 +122,9 @@
                 (stream-cdr t))
     (pairs (stream-cdr s) (stream-cdr t)))))
 
-   
+(define (integral integrand initial-value dt)
+  (define int
+    (cons-stream initial-value
+                 (add-streams (scale-stream integrand dt)
+                              int)))
+  int)