for virtualbox with xmonad

configuration.nix

# Edit this configuration file to define what should be installed on
# your system.  Help is available in the configuration.nix(5) man page
# and in the NixOS manual (accessible by running ‘nixos-help’).

{ config, pkgs, ... }:

{
  imports =
    [ # Include the results of the hardware scan.
      ./hardware-configuration.nix
    ];

  # Use the systemd-boot EFI boot loader.
  boot.loader.systemd-boot.enable = true;
  boot.loader.efi.canTouchEfiVariables = true;

  networking.hostName = "nixos"; # Define your hostname.
  networking.enableIPv6 = false;
  # networking.wireless.enable = true;  # Enables wireless support via wpa_supplicant.

  # Select internationalisation properties.
  # i18n = {
  #   consoleFont = "Lat2-Terminus16";
  #   consoleKeyMap = "us";
  #   defaultLocale = "en_US.UTF-8";
  # };

  # Set your time zone.
  time.timeZone = "Mexico/Mexico";

  # List packages installed in system profile. To search by name, run:
  # $ nix-env -qaP | grep wget
  environment.systemPackages = 
    let x11 =  if config.services.xserver.enable
               then [ pkgs.firefox pkgs.chromium ]
               else [];
        xmonad = if config.services.xserver.windowManager.xmonad.enable
                 then [ pkgs.dmenu ] else []; 
    in with pkgs; [ wget vim ] ++  x11 ++ xmonad;

  # List services that you want to enable:

  # Enable the OpenSSH daemon.
  # services.openssh.enable = true;

  # Enable CUPS to print documents.
  # services.printing.enable = true;

  # Enable the X11 windowing system.
  services.xserver.enable = true;
  # services.xserver.layout = "us";
  # services.xserver.xkbOptions = "eurosign:e";

  # Enable the KDE Desktop Environment.
  # services.xserver.displayManager.kdm.enable = true;
  # services.xserver.desktopManager.kde4.enable = true;

  services.xserver.windowManager.xmonad.enable = true;

#  environment.systemPackages = with pkgs;
#    if config.services.xserver.enable
#    then [ pkgs.firefox pkgs.chromium ]
#    else []
#    ++
#    [];
  

  # Define a user account. Don't forget to set a password with ‘passwd’.
  users.extraUsers.fehu = {
    isNormalUser = true;
    extraGroups = ["wheel"];
  #  uid = 1000;
  };

  # The NixOS release to be compatible with for stateful data such as databases.
  system.stateVersion = "16.09";

}