This doesn't really solve GP's problem, as the Nothing type is generally still equal to itself. Certainly useful for general purpose programming languages, though.

The problem is really that you're using the wrong equality type here. You get the right semantics if you use `= : A -> A -> Bool` and then apply it to a `Maybe A` and a `Maybe A` by lifting it: you end up with `Nothing` if either input was `Nothing`, and `Just answer` if both were known.