伊斯利斯的哈斯克尔版本 - 注释（爆炸符号） [英] Haskell version of Idris !-notation (bang notation)

问题描述

我最近学习了一些Idris，有一件事情非常方便，就是！-notation，它让我缩短了一个do块中的monadic代码，比如

I've had the luxury of learning a bit of Idris lately and one thing I've found extremely convenient is the !-notation, which let's me shorten monadic code inside a do block such as

a' <- a
b' <- b
c' <- c
someFunction a' b' c'

更加美好

to the much nicer

someFunction !a !b !c

现在当我在Haskell中编写代码，我正在寻找类似的东西，但据我所知它并不存在（并且爆炸字符显然已用于严格的模式匹配）。有没有什么办法可以避免在do块中有一堆琐碎的左箭头？也许是一个扩展，增加了一个重写规则，或者是这个效果？

Now when I write code in Haskell, I'm looking for something similar but as far as I can tell it doesn't exist (and the bang character is obviously already used for strict pattern matching). Is there any way to avoid having a bunch of trivial left arrows inside a do block? Perhaps an extension that adds a rewriting rule, or something to that effect?

推荐答案

由于每个monad都是应用（GHC> = 7.10），我们可以写出

Since every monad is an Applicative (with GHC >= 7.10) we can write

someFunction <$> a <*> b <*> c

请注意，如果 someFunction 返回一个monadic类型 m T 的值，上面将返回 m（m T），这可能不是我们想要的正如@pigworker指出的那样）。然而，我们可以将加入这两层：

Note that if someFunction returns a monadic value of type m T, the above will return m (m T), which is likely not what we want (as @pigworker points out below). We can however join the two layers together:

join $ someFunction <$> a <*> b <*> c

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