TypeError not raised

This error happens only sometimes. So it's an indicator of some underlying condition.

self = <test_typeclass.TestTypeclass testMethod=test_typeclasses>

    def test_typeclasses(self):
        A, B =\
                data.A == d.B & deriving(Show, Eq)
        self.assertTrue(has_instance(A, Show))
        self.assertTrue(has_instance(A, Eq))
        self.assertFalse(has_instance(A, Ord))
        with self.assertRaises(te):
            Ord[B]
        with self.assertRaises(te):
>           A, B = data.A == d.B & deriving(Show, Ord)
E           AssertionError: TypeError not raised

tests/test_typeclass.py:19: AssertionError

I guess that the underlying cause is that there's a required ordering that's not guaranteed.