lisp 从列表中过滤掉不匹配谓词的结果 [英] lisp filter out results from list not matching predicate

问题描述

我正在尝试使用 emacs 方言学习 lisp，但我有一个问题.假设 list 有一些成员，其谓词评估为假.如何在没有这些成员的情况下创建新列表?类似于 { A in L: p(A) is true }.在python中有过滤器功能，lisp中是否有等价的东西?如果没有，我该怎么做?

I am trying to learn lisp, using emacs dialect and I have a question. let us say list has some members, for which predicate evaluates to false. how do I create a new list without those members? something like { A in L: p(A) is true }. in python there is filter function, is there something equivalent in lisp? if not, how do I do it?

谢谢

推荐答案

这些函数都在 CL 包中，你需要 (require 'cl) 来使用它们:

These functions are in the CL package, you will need to (require 'cl) to use them:

(remove-if-not #'evenp '(1 2 3 4 5))

这将返回一个包含参数中所有偶数的新列表.

This will return a new list with all even numbers from the argument.

还要查找delete-if-not，它的作用相同，但修改了它的参数列表.

Also look up delete-if-not, which does the same, but modifies its argument list.

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