Managing extensions

I'd be very interested in the possibility of managing geographic data with this project. Haskell does not have native efficient libraries to handle geographic data, but there are bindings to existing c++ ones such as https://github.com/ewestern/geos.

Overall, the most interesting things with postgresql are often contained in extensions (the engine itself is quite good, but its extensibility is key to its success). What's your opinion on extensions for this project, and what's already there for them ?