The new ghc infrastructure is broken on 10.6, and at a quick glance, it looks like it starts building at 10.8, which is actually not too bad, and better than I thought: <https://ports.macports.org/port/ghc/builds>
I am not sure if i will ever get around to trying to fix the older systems, and I would doubt if anyone else ever will. It might or might not be possible to do so. There was some minor talk of resurrecting the ghc v7 infrastructure, but I think that is a dead duck idea as the whole family of hs-* ports needed for it are disappearing too. So -- you might be out-of-luck there, unless I break my leg or something :> Ken
