tcfail118.hs:10:29: error: [GHC-43085]
    • Overlapping instances for Eq Foo
        arising from the first field of ‘Bar’ (type ‘Foo’)
      Matching instances:
        instance Eq Foo -- Defined at tcfail118.hs:13:10
        instance Eq Foo -- Defined at tcfail118.hs:11:25
    • When deriving the instance for (Eq Bar)