35 lines
873 B
Haskell
35 lines
873 B
Haskell
module Moi where
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newtype Moi s a = Moi { runMoi :: s -> (a, s) }
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instance Functor (Moi s) where
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-- fmap :: (a -> b) -> Moi s a -> Moi s b
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fmap f (Moi g) = Moi (\x -> h $ g x)
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where h (a, b) = (f a, b)
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instance Applicative (Moi s) where
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-- pure :: a -> Moi s a
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pure a = Moi (\s -> (a, s))
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-- (<*>) :: Moi s (a -> b) -> Moi s a -> Moi s b
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(Moi f) <*> (Moi g) = Moi (\s -> ((fst (f s)) (fst (g s)), s))
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instance Monad (Moi s) where
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return = pure
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-- (>>=) :: Moi s a -> (a -> Moi s b) -> Moi s b
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(Moi f) >>= g = Moi (\s -> (runMoi (g (fst (f s)))) (snd (f s)))
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get :: Moi s s
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get = Moi $ \a -> (a, a)
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put :: s -> Moi s ()
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put s = Moi $ \_ -> ((), s)
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exec :: Moi s a -> s -> s
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exec (Moi sa) s = snd (sa s)
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eval :: Moi s a -> s -> a
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eval (Moi sa) s = fst (sa s)
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modify :: (s -> s) -> Moi s ()
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modify f = Moi $ \a -> ((), f a)
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