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{-# LANGUAGE NoImplicitPrelude #-}
module Control.Monad.State where
import Data.Tuple -- for fst, snd
import Data.Function -- for id
import Control.Monad
data State s a = State { runState :: s->(a,s) }
instance Monad State where
f >>= g = State (\s1 -> let (x,s2) = runState f s1 in runState g s2)
return x = State (\s -> (x,s))
mfix f = State (\state1 -> let result@(state1, x) = runState (f x) state1 in result)
unsafeInterleaveIO f = State (\state -> (state, snd $ runState f state))
get = State ( \s -> (s , s) )
put s = State ( \_ -> ((), s) )
modify f = State ( \s -> ((), f s) )
evalState x s = fst $ runState x s
execState x s = snd $ runState x s
-- mapState
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