>From the ghc-6.8.2 sources then, I'm just afraid of possible errors, and I don't have any previous ghc installed.

Do the sources permit bootstrapping? From what I know...
The source distribution needs an installed GHC (version 6.0 at least). If your platform isn't currently supported with a binary distribution, then you'll need to consult the section on Porting GHC in the Building Guide.

I'm afraid of the same error as macports 6.6.1:

configure: error: GHC is required unless bootstrapping from .hc files.