haskell - 将函数组合成另一个函数

Question

标准库中是否有一个 Haskell 函数，它接受三个函数并返回一个函数，该函数将前两个函数的返回值应用于第三个函数，如下所示:

compact :: (a -> b) -> (a -> c) -> (b -> c -> d) -> a -> d
compact a b c = \x -> c (a x) (b x)

或者这个:

import Control.Arrow
compact' :: (a -> b) -> (a -> c) -> (b -> c -> d) -> a -> d
compact' a b c = uncurry c . (a &&& b)

这样:

compact (take 1) (drop 2) (++) [1,2,3,4] == [1,3,4]
compact (+10) (*2) (<) 11 == True
compact (+10) (*2) (<) 9 == False

Answer 1

如果您将签名重新排序为:

(b -> c -> d) -> (a -> b) -> (a -> c) -> a -> d

这相当于 liftM2 ，自 ((->) r) is an instance of Monad type class

liftM2 :: Monad m => (a1 -> a2 -> r) -> m a1 -> m a2 -> m r

和

\> liftM2 (++) (take 1) (drop 2) [1, 2, 3, 4]
[1,3,4]

<小时/>

类似地，liftA2来自Control.Applicative:

liftA2 :: Applicative f => (a -> b -> c) -> f a -> f b -> f c

\> liftA2 (++) (take 1) (drop 2) [1, 2, 3, 4]
[1,3,4]