这不应该在某个图书馆吗？ [英] Shouldn't this be in a library somewhere?

问题描述

我正在编写一些代码来生成大量随机值并将它们添加到结构中，并且我需要一种机制来链接相同的IO操作。所以，我写了这个：

I was writing some code to generate a lot of random values and add them to a structure, and I needed a mechanism to chain up identical IO actions. So, I wrote this:

chain :: Monad m => Int -> (a -> m a) -> a -> m a
chain 0 _ a = return a
chain n f a = f =<< chain (n-1) f a

我怀疑这应该在某个图书馆某处，但我无法在Control.Monad中找到它。这个功能已经写好了吗？有没有更简单的方法来做到这一点？

I get a suspicion that this should be in some library somewhere, but I couldn't find it in Control.Monad. Is this function already written? Is there an easier way to do this?

推荐答案

我不知道它是否存在某处，但它可以被整齐地定义as：

I don't know if it exists somewhere, but it can be neatly defined as:

chain :: Monad m => Int -> (c -> m c) -> c -> m c
chain n = foldr (>=>) return . replicate n

中有几个潜在有用的函数（<$ c）例如，$ c> foldr（> =>）return 是 concatM ），尽管不完全是链。

monad-loops has a few potentially useful functions in that vein (foldr (>=>) return, for instance, is concatM), though not exactly your chain.

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