Thank you, Ralf. Curiosity satisfied. :) Markus -- Markus Schnell
There is just one Generic Haskell project even though the actual language extension is a moving target of course because this is an active project.
The boilerplate approach is about lightweight generic programming IN Haskell. The fact that the boilerplate approach is supported by GHC is very, very convenient, but in a sense optional: in principle, you could write Typeable and Data instances yourself, and you could still leverage generic programming in Haskell. Anyway, some more information can be found on the boilerplate page.
Using both approaches together would be quite cool!?! There is no technical reason why this would be impossible. But it is certainly not the case that the two approaches are complementary. They overlap quite a bit. The boilerplate approach tries to be easy in the traversal arena. In the literature, there are some comments on how these and other approaches relate. I would still find it interesting to see a survey that works through some examples and compares the two approaches and others.
Ralf