Yeah, I really like the single package model. And the Setup.hs does work -- I just can't use cabal 1.2.x or 1.3.x or 1.4.x with it :)
I beg to differ. We have three cabal Setup files in the repo: Setup.hs (for the 1.2 series), Setup-1162.hs, and Setup-114.hs. Setup.hs should work with ghc-6.8 out of the box, Setup-1162.hs should work with ghc-6.6 (once you've upgraded cabal to 1.1.6.2), and Setup-114 I just kept because, well, someone might find it useful. The idea is that you should upgrade cabal to the latest (currently 1.2) and use the Setup.hs, but in case you can't, the older Setup's are hanging around to help. That said, I haven't tested with the latest cabal release, so perhaps it's borken again.
What do you do if the user does not have the ODBC or the postgresql C libs installed? Do they have to have all backends installed to use just one?
No, we do something you might consider fairly hideous. Having established which libraries are installed on the user's system, we then use that list to filter the module list. So if you don't have Oracle or Sqlite installed, the module list is pruned so that these modules are no longer present in the build. This isn't stricly necessary; another approach would be to simlply build all of the modules. This works fine with ghc (which uses gnu ld for linking). However, with ghci (which has a custom module loader and linker, I think), it seems to attempt to link all of the modules in the lib, and this fails badly if you don;t have every back-end DBMS client installed. The only way I could find to fix that was to adjust the build to only include modules that will link successfully (i.e. those for which you have a DBMS client installed). Alistair