Haskell：一些和许多 [英] Haskell: some and many

问题描述

在 Control.Applicative.Alternative 某些和多 $ c>好吗？如果我写了某些$ Just 42 之类的东西，它似乎会导致无限递归，这似乎不是非常有用......

解决方案

当用作解析器组合器时，它们是有意义的。 某些表示解析器尽可能经常应用，但至少应用一次。 many 类似，但不允许解析。如果可能， Just ... 永远不会失败，因此解析器会循环。

What are some and many in Control.Applicative.Alternative good for? If I write something like some $ Just 42, it seems to cause infinite recursion, which seems not very useful...

解决方案

They make sense, when used as a parser combinator. some means, that the parser is applied as often as possible, but at least once. many is similar, but allows no parse. In case of Maybe, Just ... never "fails", thus your parser loops.

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