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26 lines
806 B
26 lines
806 B
{-# LANGUAGE InstanceSigs #-} |
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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 $ \s -> let (a, s') = g s |
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in (f a, s') |
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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 -> let (f', s') = f s |
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(a, s'') = g s' |
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in (f' a, s'') |
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instance Monad (Moi s) where |
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return :: a -> Moi s a |
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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 -> let (a, s') = f s |
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in runMoi (g a) s' |