Implement till 3.66

util.scm

@@ -68,4 +68,33 @@
   (display x)
   (newline))
 
+(define (take n xs)
+  (if (= n 0)
+    '()
+    (cons (stream-car xs)
+          (take (- n 1) (stream-cdr xs)))))
+
+(define (display-stream s)
+  (stream-for-each display-line s))
+
+(define (show x)
+  (display-line x)
+  x)
+
+(define (stream-ref s n)
+  (if (= n 0)
+      (stream-car s)
+      (stream-ref (stream-cdr s) (- n 1))))
+
+(define (partial-sums xs)
+  (cons-stream (stream-car xs)
+               (add-streams (partial-sums xs)
+                            (stream-cdr xs))))
+
+(define (scale-stream stream factor)
+  (stream-map (lambda (x) (* x factor)) stream))
+
+(define (add-streams s1 s2)
+  (stream-map + s1 s2))
+
 'util-loaded