{ pkgs ? import <nixos-unstable> {} } :
{

  pkgs = import (builtins.fetchGit {
      name = "nixos-23.05";
    url = "https://github.com/nixos/nixpkgs/";
    ref = "refs/heads/nixos-unstable";
    rev = "ef99fa5c5ed624460217c31ac4271cfb5cb2502c";
  });

  foo = pkgs.mkShell {
    # nativeBuildInputs is usually what you want -- tools you need to run
    nativeBuildInputs = with pkgs.buildPackages; [ 

      nodejs
      haxe
      mmark
      xml2rfc
      esbuild

    ];

    shellHooks = ''
        export NIX_SHELL_XRF=1
        echo -e "\n run: './make build' to build all (haxe parser + js)\n"
        echo -e "\n run: './make build javascript' to build js\n"
    '';
  };
}