您不能从Scheme中的函数返回任何内容吗? [英] Can you return nothing from a function in Scheme?

问题描述

我正在编写一个方案解释器，对于if语句，例如:

I'm writing a scheme interpreter, and in the case of an if statement such as:

(if (< 1 0) 'true)

我尝试过的所有解释器都将返回一个新提示.但是，当我对此进行编码时，对于是否存在替代表达式，我会有一个if.如果什么都没打印出来，我该怎么办?

Any interpreter I've tried just returns a new prompt. But when I coded this, I had an if for whether there was an alternative expression. What can I return in the if such that nothing gets printed?

(if (has-alternative if-expr)
  (eval (alternative if-expr))
  #f) ;; what do I return here?

推荐答案

根据

如果< test>产生#f而没有< alternate> 指定后，则结果 表达式未指定.

If <test> yields #f and no <alternate> is specified, then the result of the expression is unspecified.

因此，疯狂，退回任何您想要的东西！尽管#f或'()是我个人期望的结果.

So go wild, return anything you want! Although #f or '() are what I, personally, would expect.

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