3 Could not deduce `Eq (Foo a b)'
4 (arising from an instance declaration at drvfail004.hs:5)
5 from the context: (Ord a1, Ord b1)
6 Probable cause: missing `Eq (Foo a b)'
7 in instance declaration context
8 or missing instance declaration for `Eq (Foo a b)'
9 When checking the superclasses of an instance declaration
11 Compilation had errors