函数式程序的模块化和对象的模块化

(define random-init 1)(define (rand-update x)  (remainder (+ (* 13 x) 5) 24))(define (random-numbers op-stream)  (define (numbers last-value op-stream)    (let ((op (stream-car op-stream)))      (cond ((pair? op)             (cons-stream (cadr op)                          (numbers (cadr op)                                   (stream-cdr op-stream))))            (else (let ((next-value (rand-update last-value)))                    (cons-stream next-value                                 (numbers next-value                                          (stream-cdr op-stream))))))))  (numbers random-init op-stream))(define the-op-stream (list->stream '(generate (reset 9))))(define the-random-numbers (random-numbers the-op-stream));要查看流中的全部元素，不能用“流.scm”里定义的show-n，因为最后只有一个元素的时候，op-stream是空，但还会调用numbers过程，所以需要利用延时求值(define (show-n-2 s n)  (if (= n 0)      '()      (let ((the-s (force s)))        (cons (stream-car the-s)              (show-n-2 (delay (stream-cdr the-s)) (- n 1))))))(show-n-2 (delay the-random-numbers) 2);参考sicp-solution隐式定义的版本:(define (random-numbers op-stream)  (define numbers    (cons-stream random-init                 (stream-map                  (lambda (num op)                    (if (pair? op)                        (cadr op)                        (rand-update num)))                  numbers op-stream)))  (stream-cdr numbers))(define the-random-numbers (random-numbers the-op-stream))(show-n-2 (delay the-random-numbers) 2)