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{-# LANGUAGE DataKinds, MultiParamTypeClasses, FunctionalDependencies,
PolyKinds, UndecidableInstances, ScopedTypeVariables #-}
module T6015 where
data Proxy a = Proxy
class Value a t | a -> t where value :: Proxy a -> t
instance Value True Bool where value _ = True
instance Value a t => Value (Just a) (Maybe t)
where value _ = Just (value (Proxy :: Proxy a))
test = value (Proxy :: Proxy (Just True))
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