【SICP练习】143 练习3.81

练习3-81

原文

Exercise 3.81. Exercise 3.6 discussed generalizing the random-number generator to allow one to reset the random-number sequence so as to produce repeatable sequences of “random” numbers. Produce a stream formulation of this same generator that operates on an input stream of requests to generate a new random number or to reset the sequence to a specified value and that produces the desired stream of random numbers. Don’t use assignment in your solution.

代码

(define (random-update x) (remainder (+ (* 13 x) 5) 24))
;Value: random-update

(define random-init (random-update (expt 2 32)))
;Value: random-init

(define (random-number-generator command-stream) (define random-number (cons-stream random-init (stream-map (lambda (number command) (cond ((null? command) the-empty-stream) ((eq? command 'generator) (random-update number)) ((and (pair? command) (eq? (car command) 'reset)) (cdr command)) (else (error "bad command -- " command)))) random-number command-stream))) random-number)
;Value: random-number-generator

感谢您的访问，希望对您有所帮助。 欢迎大家关注或收藏、评论或点赞。

为使本文得到斧正和提问，转载请注明出处：
http://blog.csdn.net/nomasp

版权声明：本文为 NoMasp柯于旺 原创文章，未经许可严禁转载！欢迎访问我的博客：http://blog.csdn.net/nomasp