haskell.nix/test/stack-simple/pkgs.nix

{
  extras = hackage:
    {
      packages = {
        "transformers" = (((hackage.transformers)."0.5.6.2").revisions).default;
        "process" = (((hackage.process)."1.6.5.0").revisions).default;
        } // { stack-simple = ./stack-simple.nix; };
      };
  resolver = "lts-13.18";
  }