{...}:
with import <nixpkgs> {};
rec {
  nes-py = pkgs.callPackages ./nes-py.nix {
                                           buildPythonPackage = python37Packages.buildPythonPackage
                                         ; fetchPypi = python37Packages.fetchPypi
                                         ; gym = python37Packages.gym
                                         ; pyglet = python37Packages.pyglet
                                         ; numpy = python37Packages.numpy
                                         ; tqdm = python37Packages.tqdm
                                         ; fetchurl = fetchurl
  ;};

  gymmario = pkgs.callPackages ./gymmario.nix {
                                           buildPythonPackage = python37Packages.buildPythonPackage
                                         ; matplotlib = python37Packages.matplotlib
                                         ; nes-py = nes-py
                                         ; pyglet = python37Packages.pyglet
                                         ; numpy = python37Packages.numpy
                                         ; opencv4 = opencv-python
                                         ; tqdm = python37Packages.tqdm
                                         ; pygame = python37Packages.pygame
                                         ; fetchPypi = python37Packages.fetchPypi
                                         ; fetchurl = fetchurl
  ;};

  opencv-python = pkgs.callPackages ./opencv4.nix {
                                           buildPythonPackage = python37Packages.buildPythonPackage
                                         ; fetchPypi = python37Packages.fetchPypi
                                         ; numpy = python37Packages.numpy
                                         ; fetchurl = fetchurl
  ;};

}