stream - 显示无限流的连续项目的问题

Question

; defining stream-for-each
(define (stream-for-each proc s)
  (if (stream-null? s)
      'done
      (begin (proc (stream-car s))
        (stream-for-each (stream-cdr s)))))

; Defining a method to display the stream
(define (display-stream s)
  (stream-for-each display-line s))

(define (display-line x)
  (newline)
  (display x))

; Creating a stream that uses Newton-Raphson
; method to find the Square Root of 2
(define (sqrt-improve guess x)
  (avg guess (/ x guess)))

(define (sqrt-stream x)
  (define guesses
    (cons-stream 1.0
                 (stream-map (lambda (guess)
                              (sqrt-improve guess x))
                             guesses)))
  guesses)

现在测试它..

=> (stream-ref (sqrt-stream 2) 11)
Value: 1.414213562373095

看来流工作正常；但是当我尝试显示它时:

=> (display-stream (sqrt-stream 2))
1.
;The procedure #[compound-procedure 13 stream-for-each] 
has been called with 1 argument; it requires exactly 2 arguments.

据我所知，调用 stream-for-each 时带有 2 个参数，但我一定遗漏了一些东西。如有任何澄清，我将不胜感激。代码取自:http://mitpress.mit.edu/sicp/full-text/book/book-Z-H-24.html#%_sec_3.5.3

Answer 1

您只是在递归调用 (stream-for-each (stream-cdr s)) 中缺少一个参数。您的函数 stream-for-each 具有契约(Contract) 过程？溪流？ -> '完成 但你只提供了一个流(这是错误所说的)。