Haskell - 什么是Control.Applicative.Alternative对吗？ [英] Haskell - What is Control.Applicative.Alternative good for?

问题描述

我正在查看Haskell库中的 Applicative 类，并偶然发现 Alternative 。

I was looking at the Applicative class within Haskell libraries and stumbled across Alternative.

这个课程有什么好处？谷歌搜索没有透露任何特别有见地的东西。它似乎是完全不合适的，因为它与Applicative包捆绑在一起。

What is this class good for? A google search did not reveal anything particularly insightful. And it seems to be completely out of place, bundled as it is with the Applicative package.

有人可以发布一个你可能会使用这个类的场景吗？

Could someone please post a possible scenario where you would use this class?

推荐答案

它通常与解析器组合器一起使用。例如，如果 space 是一个匹配单个空格字符的解析器组合符，那么多个空格将会匹配连续的空格。

It's commonly used with parser combinators. For example, if space is a parser combinator that matches a single whitespace character, many space would be one that would match consecutive whitespace.

虽然我可以同意它在 Control.Applicative 中稍微不合适。

I can agree that it's slightly out of place in Control.Applicative, though.

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