Applicative型クラス

定義

code:purs(hs)

class Apply f <= Applicative f where

pure :: forall a. a -> f a

Haskellの場合

code:hs

class (Functor f) => Applicative f where

pure :: a -> f a

(<*>) :: f (a -> b) -> f a -> f b

instance例

Maybe

code:hs

instance Applicative Maybe where

pure = Just

Nothing <*> _ = Nothing

(Just f) <*> something = fmap f something

List

code:hs

instance Applicative [] where

Either

code:hs

instance Applicative Either a where

pure = Right

IO

code:hs

instance Applicative IO where

pure = return

a <*> b = do

f <- a

x <- b

return (f x)

code:hs

(IO 関数) <*> (IO 値) = do

関数 <- IO 関数

値 <- IO 値

(->) r

関連

参考