I was just trying to get Nix working after needing a version of base (GHC) newer than what I had installed.

The situation seems to have gotten a bit simpler with newer versions of the nix tools (this is of no fault of the author of this post, the post is more than a year old, their blog has great haskell stuff!).

Anyway, for haskell development you can just:

   1. Write cabal file (e.g., ./project.cabal)
   2. cabal2nix --shell . >shell.nix
   3. nix-shell

After step 3, all the required packages, including stuff like GHC, will be installed. You can use cabal however you normally do to build the project:

   4. cabal sandbox init
   5. cabal build