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{-# LANGUAGE FlexibleContexts #-}
module FailDueToGivenOverlapping where
class C a where
class D a where
dop :: a -> ()
instance C a => D [a]
-- should succeed since we can't learn anything more for 'a'
foo :: (C a, D [Int]) => a -> ()
foo x = dop [x]
class E a where
eop :: a -> ()
instance E [a] where
eop = undefined
-- should fail since we can never be sure that we learnt
-- everything about the free unification variable.
bar :: E [Int] => () -> ()
bar _ = eop [undefined]
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