Scheme中定义表达式的类型 [英] Type of Define expression in Scheme

问题描述

简单地说:我的问题是Scheme中define表达式的类型是什么?

To put it simply: My question is whats is the type of a define expression in Scheme?

举个例子:

(define x 5)

或

(define x (lambda (n) (* n n)))

这对我来说有点混乱.有人可以帮忙吗?

It's a bit confusing for me. Can anyone help?

推荐答案

In Racket define 是一种特殊形式而不是表达式，所以它本身没有值，如果您尝试执行这样的操作，您会得到一个错误:

In Racket define is a special form and not an expression, so it doesn't have a value per-se, if you try to execute something like this you'll get an error:

(display (define x 42))
=>  define: not allowed in an expression context in: (define x 42)

如果它有一个值，它会类似于 void，但这将取决于解释器的特定实现细节(我相信我看到一个解释器在 define 之后返回 #t完成)

If it were to have a value it'd be something akin to void, but that will be dependent on the particular implementation details of the interpreter (I believe I saw one interpreter return #t after a define was completed)

常量 # 被大多数具有副作用且没有有用结果的表单和过程返回

The constant #<void> is returned by most forms and procedures that have a side-effect and no useful result

规范不要详细讨论这一点，或者 - 强调它依赖于实现的声明.

The specification doesn't go into details on this point, either - reinforcing the statement that it's implementation-dependent.

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