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{-# LANGUAGE TypeSynonymInstances #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}
module T20542 where
class Foo a b where
foo :: a -> b
instance {-# OVERLAPPABLE #-} Show a => Foo a String where
foo = show
instance {-# OVERLAPPING #-} Read b => Foo String b where
foo = read
bar :: String -> String
bar = foo
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