testsuite/tests/typecheck/should_fail/tcfail121.hs


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{-# LANGUAGE FlexibleInstances #-}

module ShouldFail where

class Foo a where
  op :: a -> a

instance {-# OVERLAPPABLE #-} Foo a => Foo [a] 
instance {-# OVERLAPPING #-} Foo [Int]

foo :: Foo a => [a] -> [a]
foo x = op x
-- Correct instance depends on instantiation of 'a'