{
  description = "Example Darwin system flake";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
    nix-darwin.url = "github:LnL7/nix-darwin";
    nix-darwin.inputs.nixpkgs.follows = "nixpkgs";
    nh_darwin.url = "github:ToyVo/nh_darwin";
  };

  outputs = inputs@{ self, nix-darwin, nixpkgs, nh_darwin }:
  let
    configuration = { pkgs, ... }: {
      # List packages installed in system profile. To search by name, run:
      # $ nix-env -qaP | grep wget
      environment.systemPackages =
        [ pkgs.vim
          # Always an option
          # nh_darwin.packages.${pkgs.stdenv.hostPlatform.system}.default;
        ];

      # Alias for nh_darwin
      environment.shellAliases.nh = "nh_darwin";

      programs.nh = {
        enable = true;
        clean.enable = true;
        # Installation option once https://github.com/LnL7/nix-darwin/pull/942 is merged:
        # package = nh_darwin.packages.${pkgs.stdenv.hostPlatform.system}.default;
      };

      # Auto upgrade nix package and the daemon service.
      services.nix-daemon.enable = true;
      # nix.package = pkgs.nix;

      # Necessary for using flakes on this system.
      nix.settings.experimental-features = "nix-command flakes";

      # Create /etc/zshrc that loads the nix-darwin environment.
      programs.zsh.enable = true;  # default shell on catalina
      # programs.fish.enable = true;

      # Set Git commit hash for darwin-version.
      system.configurationRevision = self.rev or self.dirtyRev or null;

      # Used for backwards compatibility, please read the changelog before changing.
      # $ darwin-rebuild changelog
      system.stateVersion = 4;

      # The platform the configuration will be used on.
      nixpkgs.hostPlatform = "x86_64-darwin";
    };
  in
  {
    # Build darwin flake using:
    # $ darwin-rebuild build --flake .#simple
    darwinConfigurations."simple" = nix-darwin.lib.darwinSystem {
      modules = [
        configuration
        # Primary installation option:
        nh_darwin.nixDarwinModules.default
      ];
    };

    # Expose the package set, including overlays, for convenience.
    darwinPackages = self.darwinConfigurations."simple".pkgs;
  };
}