src/sicp/ex3_81.rkt

   1 #lang racket
   2
   3 (define (rand-seq init req-stream)
   4   (let ((req (stream-car req-stream)))
   5     (cond ((eq? req 'reset)
   6            (let ((new-init (stream-car (stream-cdr req-stream))))
   7              (let ((new-rand-val (rand-update new-init)))
   8                (cons-stream
   9                 new-rand-val
  10                 (rand-seq new-rand-val
  11                           (stream-cdr (stream-cdr req-stream)))))))
  12           ((eq? req 'generate)
  13            (let ((new-val (rand-update init)))
  14              (cons-stream
  15               new-val
  16               (rand-seq new-val (stream-cdr req-stream))))))))
  17