[序对的无穷流]

chapter_3/README.md

@@ -106,5 +106,8 @@
 	* P235 - [练习 3.63](./exercise_3_63.md)
 	* P235 - [练习 3.64](./exercise_3_64.scm)
 	* P235 - [练习 3.65](./exercise_3_65.scm)
+	* P235 - [序对的无穷流](./pairs_stream.scm)
+
+
 
 

chapter_3/pairs_stream.scm

@@ -0,0 +1,33 @@
+#lang racket
+
+;; P235 - [序对的无穷流]
+
+(require "stream.scm")
+(require "infinite_stream.scm")
+(require "ch3support.scm")
+
+(define (interleave s1 s2)
+  (if (stream-null? s1)
+      s2
+      (cons-stream (stream-car s1)
+                   (interleave s2 (stream-cdr s1)))))
+
+(define (pairs s t)
+  (cons-stream
+    (list (stream-car s) (stream-car t))
+    (interleave
+      (stream-map (lambda (x) (list (stream-car s) x))
+                  (stream-cdr t))
+      (pairs (stream-cdr s) (stream-cdr t)))))
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+(displayln "int-pairs")
+(define int-pairs (pairs integers integers))
+(display-stream-n int-pairs 20)
+
+(displayln "prime-pairs")
+(define prime-pairs (stream-filter (lambda (pair)
+                                     (prime? (+ (car pair) (cadr pair))))
+                                   int-pairs))
+(display-stream-n prime-pairs 20)
+