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?
This is getting into minutia now, but yes I tried the unsupported flag and as I already explained it barfed about the prelude. So I installed 7.4.2 from source but that confused cabal because my attempt to uninstall the ubuntu package with 7.4.1 in had failed with dependency-hell. Figuring out why (or even that) my packages weren't being seen was the puzzle I was referring to. The point is that we wouldn't have to be talking about this at all if people didn't move the furniture around all the time.
Likewise, the strong type system and the often helpful type error messages make it really easy to update code to work with more modern libs!
I'm also a big fan of the error messages, but it's nice to know if I caused them or somebody else did.