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{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE FunctionalDependencies #-}
module T5978 where
class C from to | from -> to where
instance C Float Char where
instance C Double Bool where
polyFoo :: (C from to) => from
polyFoo = undefined
polyBar ::
(C fromA toA, C fromB toB) =>
(toA -> toB) ->
fromA -> fromB
polyBar = undefined
monoBar :: Double
monoBar = polyBar id monoFoo
-- fromA = Float, fromB = Double, toA = toB
-- [W] C Float to, C Double to
-- => [D] to ~ Char, [D] to ~ Bool
monoFoo :: Float
monoFoo = polyFoo
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