common-lisp - 循环宏中的 "for"和 "as"关键字有什么区别吗？

Question

在 Common Lisp 中，在循环宏中，和 和 如 关键字似乎具有相同的功能:

(loop for i from 1 to 3 do (print i))
(loop as i from 1 to 3 do (print i))

我错过了一些细微的区别吗？如果没有，为什么要使用两个不同但相同的关键字呢？

Answer 1

6.1.2.1 Iteration Control :

The for and as keywords are synonyms; they can be used interchangeably. ... By convention, for introduces new iterations and as introduces iterations that depend on a previous iteration specification.

例如。:

(loop for x from 1 to 10
  as x2 = (* x x)
  as x4 = (* x2 x2)
  for y from 10 downto 1
  as y2 = (* y y)
  as y4 = (* y2 y2)
  sum (* x4 y4))

为什么？!

传统! :-)

并且...

"... a computer language is not just a way of getting a computer to perform operations, but rather ... it is a novel formal medium for expressing ideas about methodology" Abelson/Sussman "Structure and Interpretation of Computer Programs".

IOW，我们编写代码供人们(包括 6 个月后的您)阅读，而不仅仅是供计算机执行。

使您的代码更具可读性的一切都是“公平游戏”。