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5outh/plugin.hs

Last active November 25, 2016 18:23
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mapVar and plugIn functions
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plugin.hs
mapVar :: (Char -> Expr a) => Expr a -> Expr a
mapVar f (Var d) = f d
mapVar _ (Const a) = Const a
mapVar f (a :+: b) = (mapVar f a) :+: (mapVar f b)
mapVar f (a :*: b) = (mapVar f a) :*: (mapVar f b)
mapVar f (a :^: b) = (mapVar f a) :^: (mapVar f b)
mapVar f (a :/: b) = (mapVar f a) :/: (mapVar f b)
plugIn :: Char -> a -> Expr a -> Expr a
plugIn c val = mapVar (\x -> if x == c then Const val else Var x)
@TimoWilken
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Shouldn't the type signature of mapVar be (Char -> Expr a) -> Expr a -> Expr a instead of (Char -> Expr a) => Expr a -> Expr a?

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