learn-flakes-the-fun-way/flake.nix

{
  inputs.nixpkgs.url = "nixpkgs/nixos-24.05";
  outputs = {
    self,
    nixpkgs,
    ...
  }: let
    systems = ["aarch64-linux" "aarch64-darwin" "x86_64-darwin" "x86_64-linux"];
    pkgsFor = func: (nixpkgs.lib.genAttrs systems (system: (func (import nixpkgs {inherit system;}))));
  in {
    packages = pkgsFor (pkgs: {
      default = pkgs.callPackage ./what-is-my-ip.nix {};
    });

    devShells = pkgsFor (pkgs: {
      default = pkgs.mkShell {
        packages = [self.outputs.packages.${pkgs.system}.default];
        shellHook = ''
          echo "Hello, Nix!"
        '';
      };
    });
  };
}