Scheme中`define`的返回值是多少? [英] What's the return value of `define` in Scheme?

问题描述

我对Scheme中define的返回值感到好奇.所以我在球拍中写了以下几行

I'm curious about the return value of define in Scheme. So I wrote the following lines in Racket

#lang r5rs
(display (define a 3))

得到错误

 define: not allowed in an expression context in: (define a 3)

我对此有2个问题:

1. 这是否意味着define没有返回值?
2. 根据R5RS，define不是表达式.这是一个程序结构.仅表达式具有返回值，其他形式没有返回值是真的吗?

1. Does it mean that define has no return value?
2. According to R5RS, define is not an expression. It's a program structure. Is it true that only expressions have return values, and other forms don't?

推荐答案

如果一棵树掉在森林里没有人在附近听到它，它发出声音了吗?"

在可以有意义地获得返回值的任何上下文中使用define都是无效的.因此，是否具有返回值是没有意义的.您将永远无法观察到它.

It's not valid to use define in any context where a return value could meaningfully be obtained. So it's moot whether it has a return value or not; you'll never be able to observe it.

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