Haskell dependencies for custom cabal builds

[John Soo]

Hi Guix,

I’ve been working on some Haskell packages and got stuck recently and I didn’t know why until I realized the cabal files have `build-type: Custom` (http://hackage.haskell.org/package/termonad-1.1.0.0/termonad.cabal). I always get missing dependencies even though I have the dependencies listed in `inputs` (haskell-gi-base and friends in the example above). What do I need to do to fix this?

Thanks!

John