Please excuse me if anyone feels that this email isn't appropriate for this mailing list. Though these are somewhat Debian-specific questions, I thought that some Haskell folks could lent their insight. You would be the users after all.
Also see the recent discussion on glasgow-haskell-users about a library building/packaging system (which didn't really reach a conclusion).
There aren't many examples of libraries (without any binaries) that are packaged thus far. I noticed that ctklight installs stuff in /usr/share/hugs98/extentions, but it can be used with GHC also, so I am not sure why its done this way. I don't use hugs too much though, also I don't know anything about nhc.
So I'm considering sticking the *.lhs files for HUnit, for example, in /usr/share/hunit. Then people can alter their Makefiles to include that directory in either hugs or ghc, but I see one problem with that: GHC would want to compile the source files, and stick them in /usr/share/hunit, but would be unable to (because of permissions problems when users compile).
The package could install binary files, but then it would build-depend on ghc which doesn't exist for several Debian platforms. So I guess it could check to see if ghc is installed on the building computer and stick binaries in /usr/lib.
I think I would have two versions of each package: one that builds & installs a package for GHC, and one that installs source files for use with Hugs (GHCi can use the GHC package). These really are entirely different beasts, and in most cases will have zero files in common, so I think it makes sense to separate them altogether. That way you don't have to require GHC in order to install the Hugs version of the package, and vice-versa. Cheers, Simon