I am working my way through the Wizard Book Structure and Interpretation of Programming in my free evenings. All was going well, until I tried to implement streams in Chapter Three. I am using (Dr)Racket, not Scheme, so this might be my problem.

在我空闲的晚上，我正在努力学习向导书的结构和编程的解释。在我尝试在第三章实现Streams之前，一切都很顺利。我用的是(DR)球拍，而不是方案，所以这可能是我的问题。

The crux of the problem is that when I try to create streams I get a memory issue: "interactions disabled; out of memory". This suggests to me that there is something wrong with the way I am using delay.

问题的症结在于，当我尝试创建流时，我得到了一个内存问题：“交互被禁用；内存不足”。在我看来，这表明我使用延迟的方式有问题。

Thanks in advance for any advice :)

提前感谢您的任何建议：)

I have tried the code suggested in the text:

我已经尝试了文本中建议的代码：

#lang racket

(define (cons-stream a b)
  (cons a (delay b)))

(define (car-stream s)
  (car s))

(define (cdr-stream s)
  (force (cdr s)))

where I am calling Racket's delay and force. I have also tried implementing delay and force myself following the text, but I come across the same memory error.

我把球拍的延迟和武力称为。我也尝试了实现延迟和强制自己遵循文本，但我遇到了相同的记忆错误。

To test that this is all working I tried writing an infinite stream of 1s:

为了测试这一切是否正常工作，我尝试编写一个无限的1流：

(define (ones) (cons-stream 1 (ones)))

and a very large interval:

和一个非常大的间隔：

(define (interval low high)
  (if (> low high)
      null
      (cons-stream low
                   (interval (+ low 1) high))))

(define (first-integers n)
  (interval 0 n))

(define test-interval
  (first-integers 10000000000000000000000000))

To my understanding of the text, neither of these should cause problems because we only generate the streams when required. However, something I've done causes a memory issue and so I think the code tries to generate the entire stream!

根据我对文本的理解，这两种方法都不会造成问题，因为我们只在需要时才生成流。然而，我所做的一些事情导致了内存问题，所以我认为代码会尝试生成整个流！

We can not define

我们不能定义

(define (cons-stream a b)
  (cons a (delay b)))

because define creates a function cons-stream, so on every function call all arguments will be evaluated before the call is made. Which defeats the whole purpose -- b will be already evaluated.

因为定义创建了一个函数cons-stream，所以在每次调用函数时，都会在调用之前计算所有参数。这与整个目的背道而驰--b将被评估。

See also How is delay implemented?.

另见延迟是如何实现的？