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Commit d8ccd51

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added: MonadState
1 parent 7bd5f66 commit d8ccd51

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‎StateT.hs‎

Lines changed: 12 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -1,10 +1,18 @@
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{-# LANGUAGE MultiParamTypeClasses #-}
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{-# LANGUAGE FlexibleInstances #-}
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module StateT where
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import Control.Monad
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import Control.Monad.Trans
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newtype MyStateT s m a = MyStateT { runMyStateT :: s -> m (a,s) }
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class MonadTrans t where
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lift :: Monad m => m a -> t m a
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class (MonadState s m) where
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get :: m s
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put :: s -> m ()
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instance Monad m => Functor (MyStateT s m) where
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fmap = liftM
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@@ -24,6 +32,7 @@ instance MonadTrans (MyStateT s) where
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x' <- x
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return (x',s)
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get = MyStateT $ \ s -> return (s,s)
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put s = MyStateT $ \ _ -> return ((),s)
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instance Monad m => MonadState s (MyStateT s m) where
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get = MyStateT $ \ s -> return (s,s)
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put s = MyStateT $ \ _ -> return ((),s)
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