```nix

#### file configuration.nix ####

{ config, pkgs, options, ... }:
{
  programs.dconf.enable = true;

  imports =
    [
      ./hardware-configuration.nix
      ./users
    ];
    ...
}

#### file users/default.nix ####

{ config, pkgs, options, ... }:
let
    home-manager = builtins.fetchGit {
      url = "https://github.com/rycee/home-manager.git";
      ref = "release-19.09";
    };
in {

  imports =
    [
      (import "${home-manager}/nixos")
      ./joe.nix
    ];

}

#### file users/joe.nix ####

{ config, lib, pkgs, options, ... }:

{
  # Define a user account. Don't forget to set a password with ‘passwd’.
  users.users.joe = {
     isNormalUser = true;
     home         = "/home/joe";
     extraGroups  = [
      "wheel"   # Enable ‘sudo’ for the user by adding him to the wheel group
      "vboxsf"
     ];
 };

  home-manager.users.joe = { pkgs, lib, ... }: {
    dconf.settings= {
      "org/gnome/calculator" = {
        button-mode = "programming";
        show-thousands = true;
        base = 10;
        word-size = 64;
        window-position = lib.hm.gvariant.mkTuple [100 100];
      };
    }
 };
}