Now that's rapid maintenance, but it's still version hell because you've got to have that compiler installed first (even though HP is supposed to be a way to acquire haskell) and you probably haven't. You've probably got the one from the linux package which hasn't been maintained since, ooh, must have been at least a week ago, so you install the new one and you've trashed cabal. How long is that puzzle gonna take to unravel?

About 12 seconds, if you read http://www.haskell.org/platform/linux.html:

Download the source tarball for Unix-like systems: here

Get and install GHC 7.4.2 prior to building the platform:

Finally, unpack the Haskell Platform source tarball, and run (possibly with 'sudo'):

    ./configure
    make
    make install

Also, the Haskell Platform ./configure step checks which version of GHC you have installed, and requires you to pass the option --enable-unsupported-ghc-version in order to compile it with anything other than GHC 7.4.2.

Did you try an unsupported version?  And now you're complaining?