Add implementation of exercise 3-53

Author: ramsayleung

README.org

@@ -25,7 +25,7 @@
   习题完成情况:
   - 章节一: 43/46
   - 章节二: 88/97
-  - 章节三: 52/82
+  - 章节三: 53/82
   - 章节四: TODO
   - 章节五: TODO
 * 运行

chapter3/exercise3-50.rkt

@@ -9,6 +9,8 @@
        (apply stream-map
               (cons proc (map stream-cdr argstreams))))))
 
+(provide (rename-out [stream-map map-stream]))
+
 (module+ test
   (require rackunit)
 

chapter3/exercise3-53.org

@@ -0,0 +1,14 @@
+#+LATEX_CLASS: ramsay-org-article
+#+LATEX_CLASS_OPTIONS: [oneside,A4paper,12pt]
+#+AUTHOR: Ramsay Leung
+#+EMAIL: [email protected]
+#+DATE: 2025-07-27 Sun 22:22
+
+#+begin_src scheme
+  (define s (cons-stream 1 (add-stream s s)))
+#+end_src
+
+这样定义出来的 =s= 是一个流，其首元素是1，第二个元素就是 =s= 的第一个元素加上 =s= 的第一个元素，即2，第三个元素即 =s= 的第二个元素加 =s= 的第二个元素，即 =4=，以此类推:
+1 2 4 8 16 32 64 ... 
+
+可以算是一个无穷的二进制序列

chapter3/infinite-stream.rkt

@@ -1,5 +1,6 @@
 #lang racket
 (require "stream.rkt")
+(require "exercise3-50.rkt")
 
 (define (integers-starting-from n)
   (cons-stream n (integers-starting-from (+ n 1))))
@@ -16,6 +17,9 @@
              (not (divisible? x (stream-car stream))))
            (stream-cdr stream)))))
 
+(define (add-streams s1 s2)
+  (map-stream + s1 s2))
+
 (module+ test
   (require rackunit)
 
@@ -29,4 +33,14 @@
              (define primes (sieve (integers-starting-from 2)))
              (check-equal? (stream-ref primes 50) 233)
              )
+
+  (test-case "Test for infinite stream"
+             (define ones (cons-stream 1 ones))
+             (define integers (cons-stream 1 (add-streams ones integers)))
+             (define fibs (cons-stream 0
+                                       (cons-stream 1
+                                                    (add-streams (stream-cdr fibs)
+                                                                 fibs))))
+             (check-equal? (stream-ref fibs 6) 8)
+             )
   )