ref: faf4d16a06726e00ca9997479421f9fd13157e51
dir: /lib/Control/Applicative.hs/
module Control.Applicative(
Applicative(..),
(<$>), (<$), (<**>),
liftA, liftA3,
Alternative(..),
guard, asum, optional,
) where
import Primitives -- for fixity
import Data.Bool_Type
import Data.Functor
import Data.Function
import Data.List_Type
import Data.Maybe_Type
infixl 4 <*>, *>, <*, <**>
class Functor f => Applicative f where
pure :: forall a . a -> f a
(<*>) :: forall a b . f (a -> b) -> f a -> f b
(*>) :: forall a b . f a -> f b -> f b
(<*) :: forall a b . f a -> f b -> f a
liftA2 :: forall a b c . (a -> b -> c) -> f a -> f b -> f c
(<*>) = liftA2 id
a1 *> a2 = (id <$ a1) <*> a2
a1 <* a2 = const <$> a1 <*> a2
liftA2 f a b = f <$> a <*> b
liftA :: forall f a b . Applicative f => (a -> b) -> f a -> f b
liftA f a = pure f <*> a
liftA3 :: forall f a b c d . Applicative f => (a -> b -> c -> d) -> f a -> f b -> f c -> f d
liftA3 f a b c = f <$> a <*> b <*> c
(<**>) :: forall f a b . Applicative f => f a -> f (a -> b) -> f b
(<**>) = liftA2 (\ a f -> f a)
-------------------------------------------------------
infixl 3 <|>
class Applicative f => Alternative f where
empty :: forall a . f a
(<|>) :: forall a . f a -> f a -> f a
some :: forall a . f a -> f [a]
some a = (:) <$> a <*> many a
many :: forall a . f a -> f [a]
many a = some a <|> pure []
guard :: forall f a . Alternative f => Bool -> f ()
guard b = if b then pure () else empty
asum :: forall f a . Alternative f => [f a] -> f a
asum [] = empty
asum (a:as) = a <|> asum as
optional :: forall f a . Alternative f => f a -> f (Maybe a)
optional a = Just <$> a <|> pure Nothing