Hi guys:

I donīt know how difficult really is, but it seens that it could be done because all the necessary elements are there (except perhaps the mapping package name-hackage url): Why hasnīt been done yet Is unknown to me. 

It would be very useful and a big save of time  to have a cabal commad "chech-dependencies-and-install-them-by-downloading-them-from-hackage-then-configure-build-and-install-this-package?. The unix installers do is t from binaries and are obsolete, so I have to do it manually with cabal everytime  when i download a new compiler version  from haskell.org. 

Cheers
  Alberto.