nixpkgs.nix

{ config, pkgs, ... }:

let
  sourceUnstable = "https://github.com/NixOS/nixpkgs-channels/archive/nixos-unstable.tar.gz";
  tarballUnstable = fetchTarball sourceUnstable;
  source1903 = "https://github.com/NixOS/nixpkgs-channels/archive/nixos-19.03.tar.gz";
  tarball1903 = fetchTarball source1903;
in {
  nixpkgs = {
    config = {
      allowUnfree = true;
      packageOverrides = pkgs: {
        unstable = import tarballUnstable { config = config.nixpkgs.config; };
        stable1903 = import tarball1903 { config = config.nixpkgs.config; };
      };
    };
  };
}