Haskell Platform on a fresh Ubuntu install

With newly-installed Ubuntu 9.10, I attempted to install version 2009.2.0.2 of the Haskell Platform, but the build of mtl failed:

Could not find module `Control.Monad'

But ghci knew about Control.Monad!

Prelude> :m + Control.Monad
Prelude Control.Monad>

Google searches yielded no relevant hits. I did find Installing haskell-platform in Ubuntu 9.10 “Karmic Koala” by David Siegel, where he mentions installing prerequisites:

sudo apt-get install ghc6 ghc6-prof ghc6-doc haddock libglut-dev happy alex \
  libedit-dev zlib1g-dev checkinstall

Even with these packages in place, the build continued to fail with the same error.

In an earlier iteration, I had installed libghc6-mtl-dev from APT, but after removing it, the mtl build succeeded along with the rest of the Haskell Platform!

The problem is the Haskell Platform build wants to install packages with and without profiling, but this means you also need profiling versions of all the prerequisite Haskell packages. (Note the presence of ghc6-prof in the above apt-get command.)

Cabal could have saved me lots of headscratching by telling me in its error message that it couldn't find a profiling version of Control.Monad!