{
    pkgs ? import (fetchTarball {
        name = "nixpkgs-21-05";
        url = "https://github.com/NixOS/nixpkgs/archive/7e9b0dff974c89e070da1ad85713ff3c20b0ca97.tar.gz";
        sha256 = "1ckzhh24mgz6jd1xhfgx0i9mijk6xjqxwsshnvq789xsavrmsc36";
    }) {},
    system ? builtins.currentSystem,
}:
    {
        pkgs = pkgs;
        system = system;
    }