sunlight checks your Cabalized package and ensures that it actually builds and passes its tests, even against mulitple dependency versions specified in your Cabal file. For example, your Cabal file might say that your package builds against base-4.5.1.0 and base-4.6.0.1. With sunlight you can automatically verify that this is actually the case. For more information, please see http://www.github.com/massysett/sunlight