计划及浅连结 [英] Scheme and Shallow Binding

问题描述

 (define make (lambda (x) (lambda (y) (cons x (list y)))))

 (let ((x 7)
       (p (make 4)))
   (cons x (p 0)))

我新的计划和方案的功能，所以我有点笨重通过程序走，但我得到，如果我用深结合这一计划将返回（7 4 0）。说得通。你会这个程序做使用浅约束力？我得到这听起来愚蠢的，但在与利弊重新定义了一行P？因此，在这种情况下，我们将返回（7 0）？

I'm new to Scheme and functional program, so I am a bit clunky with walking through programs, but I get that if I used deep binding this program will return (7 4 0). Makes sense. What would this program do using shallow binding? I get this may sound dumb but is the p in the line with cons a redefinition? So in that case, we would return (7 0)?

基本上，我明白了深V的概念。浅约束力，但我觉得我混杂起来看方案时，因为我不是疯了熟悉它。

Basically, I understand the concept of deep v. shallow binding, but I feel like I'm jumbling it up when looking at Scheme because I'm not crazy familiar with it.

推荐答案

请参阅此维基百科的有关范围界定的讨论文章（它提到词法/动态范围和深/浅绑定）铭记计划是词法范围。将内斯的回答提供了更多信息。
现在，让我们来看看一步一步发生的事情在这个片段中code的：

See this wikipedia article for a discussion on scoping (it mentions lexical/dynamic scoping and deep/shallow binding) bearing in mind that Scheme is lexically scoped. Will Ness' answer provides additional information. For now, let's see step-by-step what's happening in this snippet of code:

; a variable called x is defined and assigned the value 7
(let ((x 7)
; make is called and returns a procedure p, inside its x variable has value 4
      (p (make 4)))
; 7 is appended at the head of the result of calling p with y = 0
  (cons x (p 0)))

=> '(7 4 0)

请注意，在第二行的闭合的在，由返回的拉姆达制造和变量 X创建内将被分配值 4 。这 X 无关与外 X ，因为方案是词法范围。

Notice that in the second line a closure is created in the lambda returned by make, and the variable x inside will be assigned the value 4. This x has nothing to do with the outer x, because Scheme is lexically scoped.

最后一行是不是重新定义，在previous段落内所提到的 X 制作从 X定义在的让前pression。

The last line is not a redefinition, as mentioned in the previous paragraph the x inside make is different from the x defined in the let expression.

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