Couldn't cabal install without happy and alex

[hardbyte]

On archlinux with a freshly installed and updated cabal calab install pandoc failed with the following message:

Configuring pandoc-1.12.4.2...
setup: The program alex is required but it could not be found.
cabal: Error: some packages failed to install:
pandoc-1.12.4.2 failed during the configure step. The exception was:
ExitFailure 1

After manually installing alex the same message occurred for happy. Then pandoc installed fine.

I see alex and happy are listed as build tools and not as build dependencies.

[jgm]

Quoth the INSTALL file:

1.  Install the [Haskell platform].  This will give you [GHC] and
    the [cabal-install] build tool, as well as `alex` and `happy`.
    If you do not use the Haskell platform, you'll need to install
    `alex` and `happy` separately:

        cabal install alex happy

I think that listing them as build-tools is the correct thing to do, but cabal doesn't do the right thing and install them before proceeding. There's an open issue for this: haskell/cabal#220.

So, no bug here as far as I can see...