33 lines
863 B
Haskell
33 lines
863 B
Haskell
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module Product where
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import Pretty
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data Product xs where
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Nil :: Product '[]
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Cons :: { pHead :: x, pTail :: Product xs } -> Product (x : xs)
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instance Pretty (Product xs) => Show (Product xs) where
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show = show . PP
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class Contains x xs where
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getElem :: Product xs -> x
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putElem :: x -> Product xs -> Product xs
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instance {-# OVERLAPS #-} Contains x (x : xs) where
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getElem (Cons x _) = x
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putElem x (Cons _ xs) = Cons x xs
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instance Contains x xs => Contains x (y : xs) where
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getElem (Cons _ xs) = getElem xs
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putElem x (Cons y xs) = Cons y (putElem x xs)
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modifyElem :: Contains x xs => (x -> x) -> Product xs -> Product xs
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modifyElem f xs = putElem (f $ getElem xs) xs
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instance Pretty (Product '[]) where
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pp _ = "{}"
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instance (Pretty x, Pretty (Product xs)) => Pretty (Product (x : xs)) where
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pp (Cons x xs) = pp x <+> "&" <+> pp xs
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