【SICP练习】120 练习3.51

练习3-51

原文

Exercise 3.51. In order to take a closer look at delayed evaluation, we will use the following procedure, which simply returns its argument after printing it:

(define (show x) 
   (display-line x) 
   x)

What does the interpreter print in response to evaluating each expression in the following sequence?

(define x (stream-map show (stream-enumerate-interval 0 10))) (stream-ref x 5) 
(stream-ref x 7)

代码

(define (show x)
  (display-line x)
  x)

(define x (stream-map show (stream-enumerate-interval 0 10)))

0
;Value: x

(stream-ref x 5)

1
2
3
4
5

;Value: 5

(stream-ref x 7)

6
7
;Value: 7

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