Endo型

code:hs

-- Endo :: (a -> a) -> Endo a

newtype Endo a = Endo { appEndo :: a -> a }

code:ts

type Endo<T> = (x: T) => T;

instance

code:hs

instance Semigroup a => Semigroup (Endo a) where

Endo f <> Endo g = Endo (f . g)

code:hs

instance Monoid (Endo a) where

mempty = Endo id