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|
{-# LANGUAGE DeriveFunctor #-}
{-# LANGUAGE UnboxedTuples #-}
module State where
import GhcPrelude
newtype State s a = State { runState' :: s -> (# a, s #) }
deriving (Functor)
instance Applicative (State s) where
pure x = State $ \s -> (# x, s #)
m <*> n = State $ \s -> case runState' m s of
(# f, s' #) -> case runState' n s' of
(# x, s'' #) -> (# f x, s'' #)
instance Monad (State s) where
m >>= n = State $ \s -> case runState' m s of
(# r, s' #) -> runState' (n r) s'
get :: State s s
get = State $ \s -> (# s, s #)
gets :: (s -> a) -> State s a
gets f = State $ \s -> (# f s, s #)
put :: s -> State s ()
put s' = State $ \_ -> (# (), s' #)
modify :: (s -> s) -> State s ()
modify f = State $ \s -> (# (), f s #)
evalState :: State s a -> s -> a
evalState s i = case runState' s i of
(# a, _ #) -> a
execState :: State s a -> s -> s
execState s i = case runState' s i of
(# _, s' #) -> s'
runState :: State s a -> s -> (a, s)
runState s i = case runState' s i of
(# a, s' #) -> (a, s')
|
