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{-# LANGUAGE Haskell2010 #-}
{-# LANGUAGE MultiParamTypeClasses, UndecidableInstances #-}
module Bug where
class A a oops
data D d = D d
instance A a oops => Read (D a)
-- Actually this instance is ambiguous
-- and is now rightly rejected
data E e = E (D e) deriving Read
instance A Int Bool
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