或作为方案中的程序 [英] or as procedure in scheme

问题描述

我想将 or 应用于列表的每个元素，例如:(apply or '(#t #t #f)) 预期结果 #t，但出现错误:

I want to apply or to every element of list, example: (apply or '(#t #t #f)) expected result #t, but I'm getting error:

'#' 到 'apply' 的类型错误(kawa.lang.Macro)(预期:过程、序列或其他运算符)

'#' to 'apply' has wrong type (kawa.lang.Macro) (expected: procedure, sequence, or other operator)

据我所知，or 不是一个程序.有没有什么程序可以代替或?

As I understand or is not a procedure. Is there any procedure that can be used instead of or?

推荐答案

最简单的方法是使用 exists*.无论何时使用 (apply or some-list)，都可以使用 (exists values some-list).或者，如果您愿意，您可以定义一个使用 exists 来执行此操作的函数:

The easiest way to do this is with exists*. Whenever you would use (apply or some-list), you can use (exists values some-list). Or if you like, you can define a function that uses exists to do that:

#!r6rs
(import (rnrs base)
        (rnrs lists))

(define (or* . lst)
  (exists values lst))

values 是恒等函数，所以 (values x) 就是 x.

values is the identity function, so (values x) is just x.

exists 是一个高阶函数，定义为 (exists f (list x ...)) 等价于 (or (fx) ...).

exists is a higher-order function defined so that (exists f (list x ...)) is equivalent to (or (f x) ...).

例如 (exists values (list #t #t #f)) 等价于 (or (values #t) (values #t) (values #f))，与 (or #t #t #f) 相同.

For example (exists values (list #t #t #f)) is equivalent to (or (values #t) (values #t) (values #f)), which is the same as (or #t #t #f).

尝试一下:

> (apply or* '(#t #t #f))
#t
> (apply or* '(#f #f #f))
#f
> (or* #t #t #f)
#t
> (or*)
#f

*exists 有时被称为 ormap 或 any

*exists is sometimes known as ormap or any

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