testsuite/tests/typecheck/should_fail/tcfail121.hs

   1
   2 {-# LANGUAGE FlexibleInstances #-}
   3
   4 module ShouldFail where
   5
   6 class Foo a where
   7   op :: a -> a
   8
   9 instance {-# OVERLAPPABLE #-} Foo a => Foo [a]
  10 instance {-# OVERLAPPING #-} Foo [Int]
  11
  12 foo :: Foo a => [a] -> [a]
  13 foo x = op x
  14 -- Correct instance depends on instantiation of 'a'