let
  lock = builtins.fromJSON (builtins.readFile ./flake.lock);
  nixpkgs' = fetchTarball {
    url = lock.nodes.nixpkgs.locked.url or "https://github.com/NixOS/nixpkgs/archive/${lock.nodes.nixpkgs.locked.rev}.tar.gz";
    sha256 = lock.nodes.nixpkgs.locked.narHash;
  };
in
  {
    nixpkgs ?
      import nixpkgs' {
        config = {};
        overlays = [];
        inherit system;
      },
    system ? builtins.currentSystem,
  }: let
    # fixed point wizardry
    pkgs' = import ./overlay.nix (nixpkgs // pkgs') nixpkgs;
  in
    pkgs'