我该如何申请“或"?到elisp中的列表 [英] How do I apply "or" to a list in elisp

问题描述

在elisp中，我可以像+一样求值或作为函数.

In elisp I can evaluate or as a function just like +.

(or nil 0 nil) ==> 0

(+ 1 0 1) ==> 2

我可以使用Apply将+应用于列表

I can use apply to apply + to a list

(apply '+ '(1 0 1)) ==> 2

所以，我会以相同的方式思考或工作，但事实并非如此.

So, I would think or would work the same way, but it doesn't.

(apply 'or '(nil 0 nil)) ==> error: (invalid-function or)

我想象这是由一些用于实施短路评估的内部魔术所引起的.如何使用apply在列表上执行或操作?

I imagine this comes from some internal magic used to implement the short-circuit evaluation. How can I use apply to execute the or operation over a list?

P.S.我想要的应用程序是查找命令行上是否有任何元素与特定模式匹配，因此我正在编写的重要部分是:

P.S. my desired application is to find out whether any elements on the command line match a particular pattern, so the important part of what I am writing is:

(apply 'or (mapcar (lambda (x) (string-match-p "pattern" x)) command-line-args))

但这不起作用

推荐答案

问题是or是一个宏(这是有问题的内部魔术")，而您正确地做到了这一点，因此它可以做短路.如果or是一个函数，则对其进行调用将需要遵循评估函数调用的通常规则:在进行调用之前，所有参数都需要进行求值.

The problem is that or is a macro (which is the "internal magic" in question), and you're right that that's done so it can do short-circuiting. If or was a function, then calling it would need to follow the usual rules for evaluating a function call: all the arguments would need to get evaluated before the call is made.

另请参见此问题- -这是关于Scheme的，但问题完全相同.

See also this question -- it's about Scheme but it's the exact same issue.

对于解决方案，您可能应该使用some，如:

As for a solution, you should probably use some, as in:

(some (lambda (x) (string-match-p "pattern" x)) command-line-args)

注意:这使用默认情况下emacs中不包含的通用lisp.只需使用(require 'cl)

Note: this uses common lisp that is not included in emacs by default. Just use (require 'cl)

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