haskell-pkgs.nix

let
  # Fetch the latest haskell.nix and import its default.nix
  haskellNix = import
    (builtins.fetchTarball {
      url = "https://github.com/input-output-hk/haskell.nix/archive/cc40a24585ccba274dc9a5af96d5506034e0d658.tar.gz";
    })
    { };

  # haskell.nix provides access to the nixpkgs pins which are used by our CI,
  # hence you will be more likely to get cache hits when using these.
  # But you can also just use your own, e.g. '<nixpkgs>'.
  nixpkgsSrc = haskellNix.sources.nixpkgs-2111;

  # haskell.nix provides some arguments to be passed to nixpkgs, including some
  # patches and also the haskell.nix functionality itself as an overlay.
  nixpkgsArgs = haskellNix.nixpkgsArgs;

  # import nixpkgs with overlays
in
import nixpkgsSrc nixpkgsArgs