Hi Henning,
Uniplate is simple (only multi parameter type classes, and even then only in a very simple usage), fast (one of the fastest generics libraries) and concise (probably the most concise generics library). It's also not as powerful as most of the other generics libraries, but I find it does about 98% of the generics tasks I need. Uniplate is used extensively in virtually all my tools, for example HLint.
Must a package import Uniplate, if it uses Uniplate generics, or is it a preprocessor like I sketched?
Uniplate is a library, not a preprocessor. To depend on uniplate simply add it to your cabal file, and import the correct module. There is no preprocessor, and there are no wacky extensions. If you restrict yourself to some part of the library it's even totally Haskell 98, but none of it's not Haskell 2011.
As an example, I guess your function returns all the Int's embedded within a data type, at any level?
I abstracted the Bin example from GHC's generic extension introduction:
That's one thing Uniplate can't do. But if you want a preprocessor to generate Binary instances can I recommend Derive (http://community.haskell.org/~ndm/derive). Thanks, Neil