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{-# LANGUAGE MultiParamTypeClasses, FlexibleInstances #-}
module Tcfail218 where
class C a b where foo :: (a,b)
instance C [Int] Bool where foo = undefined
instance C [a] b where foo = undefined
instance {-# INCOHERENT #-} C a Int where foo = undefined
x :: ([a],Bool)
-- Needs C [a] b.
-- Should fail, as a more specific, unifying but not matching
-- non-incoherent instance exists, namely C [Int] Bool
x = foo
-- Needs C [a] Int.
-- Should succeed, because two instances match, but one is incoherent
y :: ([a],Int)
y = foo
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