As I understand it, the corresponding section of the nixpkgs manual is being written as we speak; when this is done, it should reflect the new haskell infrastructure which was merged a few months ago (no longer called haskell-ng any more btw). In the meantime, here are a few links to get you started:

https://twitter.com/garbas/status/601717689225187328 -- a recent presentation w/ accompanying slides introducing Nix's new haskell infrastructure by github.com/peti, the maintainer

https://nixos.org/wiki/Haskell

http://wiki.ocharles.org.uk/Nix

http://stackoverflow.com/questions/29033580/how-do-i-use-the...

Nix wiki lists some: https://nixos.org/wiki/Haskell#Other_resources.