{
  description = "the meat (package) manager";

  inputs = {
    # use registry nixpkgs
    # nixpkgs.url = "nixpkgs/nixos-unstable";

    src = {
      url = "path:src";
      flake = false;
    };
  };

  outputs = {
    self,
    nixpkgs,
    src,
  }: let
    # System types to support.
    supportedSystems = ["x86_64-linux" "x86_64-darwin" "aarch64-linux" "aarch64-darwin"];

    # Helper function to generate an attrset '{ x86_64-linux = f "x86_64-linux"; ... }'.
    forAllSystems = nixpkgs.lib.genAttrs supportedSystems;

    # Nixpkgs instantiated for supported system types.
    nixpkgsFor = forAllSystems (system:
      import nixpkgs {
        inherit system;
        # overlays = [self.overlay];
      });
  in {
    # Provide some binary packages for selected system types.
    packages = forAllSystems (system: let
      pkgs = nixpkgsFor.${system};
    in {
      meat = pkgs.callPackage ./meat.nix {
        inherit src;
      };
    });

    # The default package for 'nix build'. This makes sense if the
    # flake provides only one package or there is a clear "main"
    # package.
    defaultPackage = forAllSystems (system: self.packages.${system}.meat);

    # A NixOS module, if applicable (e.g. if the package provides a system service).
    nixosModules.meat = {
      pkgs,
      config,
      ...
    }: {
      options.programs.meat = with pkgs.lib; {
        flake = mkOption {
          type = with types; nullOr (either path str);
          default = null;
          description = "path to your system flake";
        };
      };
      config = {
        environment.systemPackages = [self.defaultPackage.${pkgs.system}];
        environment.sessionVariables = let
          cfg = config.programs.meat;
        in {
          FLAKE =
            if (cfg.flake == null)
            then throw "Please set the programs.meat.flake option to your system flake."
            else config.programs.meat.flake;
        };
      };
    };

    # Tests run by 'nix flake check' and by Hydra.
  };
}