Due to a problem with the template-haskell package and Cabal, you
cannot cabal-install the emgm package with GHC 6.8. However, take
heart! EMGM works very well with GHC 6.8. You merely have to download
the tar.gz package from Hackage yourself, build it, and install it.
if not, perhaps you might want to add your experience to
http://hackage.haskell.org/trac/hackage/ticket/326
Cabal should support Cabal-version-dependent Setup.hs
I thought I had worked around it, too. Unfortunately, I can only test once I upload it to Hackage. Once I had, I discovered it wasn't fixed, yet. :-/
It's a problem with cabal-install/Cabal dealing with the lack of version dependencies in template-haskell. Even though I have template-haskell >= 2.2 in my build-depends, cabal-install insists on trying to install 2.3, which of course fails when you're using GHC 6.8.
Perhaps my problem cannot be fixed within the Setup.lhs? Maybe cabal-install/Cabal is resolving dependencies solely based on the .cabal file? I don't know.
There's a sketched hack-around at the end, using Setup.hs only to call to separate Setup-version.hs files, to circumvent Cabal API
instabilities. Not nice, but perhaps better than to bypass Cabal
alltogether? One would also have to pass parameters, and the
Process API has changed in the meantime.., which I why I still
think Cabal itself should simply be able to pick cabal-versioned configuration and setup files, if they exist.