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kcsongor/Overlapping.hs

Created November 30, 2017 11:43
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Overlapping.hs
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}
module Overlapping where
class C a b where
f :: a -> b -> Bool
instance C a b where
f _ _ = False
instance {-# OVERLAPPING #-} C a a where
f _ _ = True
-- >>> f 'a' 'b'
-- True
--
-- >>> f 'a' "starfish"
-- False
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