I haven't heard anyone mention this yet, and it's a biggie, so I guess I'd better de-lurk and explain it. The issue is this: There is a legal distinction between static and dynamic linking, or at least some licenses (the GPL is the one I'm aware of) believe that there is. In particular, they assert that you are legally creating a "derived work" if you statically link with their library, and that your library, even if it's just a thin bindings wrapper, must therefore comply by their license terms. They make no such claim for dynamic linking. Of course, Haskell on most platforms and default configurations links everything statically! So I believe this means that you have to comply by the licenses of all your dependencies! Now, there's a difference between complying by those licenses and being under them yourself, but for example I believe this means that if we have a package named "hs-save-the-whales" that is under the GPL, and a front-end package "hs-redeem-them-for-valuable-cash-prizes" which makes use of the functionality in hs-save-the-whales, the front-end MUST be offered under the GPL, and, additionally, CANNOT be offered under BSD (I think). I think it would be a very useful and valuable thing for Cabal to detect this situation and warn appropriately! Contamination by undesired licenses is a serious flaw in the packaging of a package; it just happens to be a legal flaw rather than a technical one. Indeed, I would argue that this is far more important than any hypothetical per-file licensing. -- Dan Knapp "An infallible method of conciliating a tiger is to allow oneself to be devoured." (Konrad Adenauer)