如何映射一对/元组? [英] How to map over a Pair/Tuple?

问题描述

在 Haskell 中，我会做 join (***).在 Idris 中，flatten (***) 不起作用((***) 很复杂).

In Haskell I would do join (***). In Idris flatten (***) does not work ((***) is complicated).

推荐答案

在 Idris 中，没有 Functor/Applicative/Monad 实例用于<代码>r ->_ 和 -> 没有 Arrow 实例，只能通过 Morphism，所以使用flatten来做\外汇 ->f x x 导致非常冗长的代码，充满了从/到 Morphism.

In Idris, there's no Functor/Applicative/Monad instances for r -> _ and no Arrow instance for ->, only via Morphism, so using flatten to do \f x -> f x x leads to horribly verbose code full of going from/to Morphism.

你可以做到，当然，我只是不确定它是否值得......比较一下:

You can do it, of course, I'm just not sure it's worth it... compare this:

import Control.Arrow
import Data.Morphisms

both : (a -> b) -> (a, a) -> (b, b)
both = applyMor . applyMor (flatten (Mor (Mor . (***)))) . Mor

为此:

both : (a -> b) -> (a, a) -> (b, b)
both f (x, y) = (f x, f y)

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