[Haskell-cafe] Unique Ordered Types

Hi I'm experimenting with a unit system in haskell where users can add "base units". I want to reduce units after multiplication and bring it into a canonical form. The problem is what kind of types can the units have. 1) data UnitA data UnitB Problem: They can't be ordered so UnitA * UnitB can be compared to UnitB * UnitA, but I can't make a canonical form, which would make type inference a lot better. 2) type UnitA = Zero type UnitB = Suc Zero Problem: Now they can be ordered. But users can create conflicting "basic units" Silvio