[Haskell-cafe] type trickery

Hello haskell-cafe! After making "data Number = Zero | Succ Number" an instance of Integral, I wondered how I could do the same with galois fields. So starting with Z mod p, I figured I'd need something like this data GF = GF Integer Integer so that each element of the finite field would remember p. However I can't think of a way to use the typesystem to ensure that p is always the same. I think that would need an infinite number of different types, but the type hackers here probably know something better. Adrian