1-default.nix

with import <nixpkgs> {}; 

stdenv.mkDerivation {
      name = "VulkanExamples";
      buildDepends = [ cmake libxcb pkgconfig ];
}

2-default.nix

with import <nixpkgs> {}; 

let
  self = stdenv.mkDerivation {
      name = "VulkanExamples";
      buildDepends = [ cmake libxcb pkgconfig ];
  };
in self

3-default.nix

with import <nixpkgs> {};

{
  foo = callPackage ./3-foo.nix {};
}

3-foo.nix

{ stdenv, libxcb, pkgconfig, cmake }:

stdenv.mkDerivation rec {
      name = "VulkanExamples";
      buildDepends = [ cmake libxcb pkgconfig ];
}