If you're willing to go a completely different route from GHC.Generics, then you might be interested in the paper Generic Programming with Multiple Parameters [1] (whose existence I just learned of—thanks to Pedro, the author, for pointing it out to me). It does present a single Generic class that is capable of working over any number of type parameters, although the interface presented is significantly more complex than the current GHC.Generics. The only reason I mention backwards compatibility is that if we are going to introduce a GHC.Generics 2.0 some day, it'd be nice to have a way to subsume the old interface with the new one, and fortunately, the aforementioned paper includes an algorithm for doing so. My hope was that we'd be able to incorporate these ideas into a design that also grants the ability to write Generic instances for GADTs, but I don't think GHC has a fancy enough type system to do this satisfactorily at the moment. Ryan S. ----- [1] http://dreixel.net/research/pdf/gpmp_colour.pdf