#include "containers.h"
module Utils.Containers.Internal.State where
import Control.Monad (ap, liftM2)
import Control.Applicative (liftA)
import Utils.Containers.Internal.Prelude
import Prelude ()
newtype State s a = State {runState :: s -> (s, a)}
instance Functor (State s) where
fmap = liftA
instance Monad (State s) where
return = pure
m >>= k = State $ \ s -> case runState m s of
(s', x) -> runState (k x) s'
instance Applicative (State s) where
pure x = State $ \ s -> (s, x)
(<*>) = ap
m *> n = State $ \s -> case runState m s of
(s', _) -> runState n s'
#if MIN_VERSION_base(4,10,0)
liftA2 = liftM2
#endif
execState :: State s a -> s -> a
execState m x = snd (runState m x)