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{-# LANGUAGE UndecidableInstances, FlexibleContexts,
MultiParamTypeClasses, FunctionalDependencies #-}
-- The Show instance for S would have form
-- instance X T c => Show S
-- which is hard to deal with. It sent GHC 5.01 into
-- an infinite loop; now it should be rejected.
module ShouldFail where
data T = T Integer
class X a b | a -> b where
f :: a -> b
instance X T c => Show T where
show _ = ""
data S = S T deriving Show
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