readme.md

$ nix-instantiate --eval test.nix --strict
  { noOrder = [ "lumina" "gnome3" "plasma5" ]; order = [ "gnome3" "plasma5" "lumina" ]; }

test.nix

let
  lib = import <nixpkgs/lib>;
  noOrder = import <nixpkgs/nixos/lib/eval-config.nix> {
    modules = [
      {
        options.list = with lib; mkOption {
          type = with types; listOf str;
          description = "";
          default = [];
        };
      }
      {
        config.list = [ "plasma5" ];
      }
      {
        config.list = [ "gnome3" ];
      }
      {
        config.list = [ "lumina" ];
      }
    ];
  };
  order = import <nixpkgs/nixos/lib/eval-config.nix> {
    modules = [
      {
        options.list = with lib; mkOption {
          type = with types; listOf str;
          description = "";
          default = [];
        };
      }
      {
        config.list = lib.mkOrder 910 [ "plasma5" ];
      }
      {
        config.list = lib.mkOrder 900 [ "gnome3" ];
      }
      {
        config.list = lib.mkOrder 920 [ "lumina" ];
      }
    ];
  };
in {
  noOrder = noOrder.config.list;
  order = order.config.list;
}