PolyKind issue in GHC 7.6.1rc1: How to make a kind a functional dependency?

[Simon Peyton-Jones]

| Iavor and I collaborated on the design of the building blocks of
| singleton types, as we wanted our work to be interoperable. A recent
| scan through TypeLits tells me, though, that somewhere along the way,
| our designs diverged a bit. Somewhere on the to-do list is to re-unify
| the interfaces, and actually just to import TypeLits into
| Data.Singletons so the definitions are one and the same. Iavor, I'm
| happy to talk about the details if you are.

That would be good!

Simon