为什么在PLT-Scheme 372中'(a.b.c)评估为(bac)? [英] Why does '(a . b . c) evaluate to (b a c) in PLT-Scheme 372?

问题描述

我试图了解对，缺点，点分元组和正确列表之间的关系PLT-方案372.我的问题的详细上下文如下:

I'm trying to understand the relations between pair, cons, dotted tuples and proper list in PLT-Scheme 372. The detailed context of my question is as follows:

在阅读了一些教科书并进行反复试验后，我得到了以下理解和直观的想法(我可能是错的...):

After reading some textbook and doing trial-and-error, I have got the following understanding and intuitive ideas (I may be wrong...):

1. 所有列表都是成对的，例如:

1. all lists are pairs, e.g.:

(pair? (list 'a 'b 'c)) => #t

所有优点都是成对的，例如:

all conses are pairs, e.g.:

(pair? (cons 'a (cons 'b 'c))) => #t

一些点分隔的元组是成对的，例如:

some dot-separated tuples are pairs, e.g.:

(pair? '(a . b)) => #t
(pair? '(a . b . c)) => #t 在标准R5RS中，这不是合法语法.

然后我碰到了这个问题:为什么'(a.b.c)求和(b a c)?在哪里可以找到点的完整使用手册?

Then I bumped into this problem: Why does '(a . b . c) evaluate to (b a c)? Where can I find a complete usage manual of dot?

'(a . b)                => (a . b)   
'(a . b . c)            => (b a c)
'(a . b . c . d)        => illegal use of `.'
'(cons 'a (cons 'b 'c)) => (a b . c)

推荐答案

对于球拍(PLT)，有一个很好的描述此处.

For Racket (PLT), there is a good description here.

关于语法(a . b . c)，请参见页面底部，它是特定于球拍的阅读器扩展，旨在将诸如(< 1 2)的典型测试表示为(1 . < . 2).

Regarding the syntax (a . b . c) look at the bottom of the page, it's a Racket-specific reader extension designed to express typical tests like (< 1 2) as (1 . < . 2).

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