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
    ];

  # List packages installed in system profile. To search, run:
  # $ nix search wget
  environment.systemPackages = with pkgs; [
    xorg.xinit dmenu emacs haskellPackages.xmobar
    # ...
  ];

  # List services that you want to enable:

  # Enable the X11 windowing system.
  services.xserver.enable = true;
  services.xserver.autorun = false;
  services.xserver.layout = "us";
  services.xserver.xkbVariant = "altgr-intl";

  # Enable touchpad support.
  # services.xserver.libinput.enable = true;

  # Enable XMonad.
  services.xserver.windowManager.xmonad = {
    enable = true;
    enableContribAndExtras = true;
  };

  # Define a user account. Don't forget to set a password with ‘passwd’.
  users.users.unyu = {
    isNormalUser = true;
    uid = 1000;
    extraGroups = ["wheel" "audio" "video"];
    createHome = true;
    shell = pkgs.zsh;
  };

  # This value determines the NixOS release with which your system is to be
  # compatible, in order to avoid breaking some software such as database
  # servers. You should change this only after NixOS release notes say you
  # should.
  system.stateVersion = "18.09"; # Did you read the comment?

}

xmonad.hs

module Main where

import XMonad
import XMonad.Config.Desktop
import XMonad.Hooks.DynamicLog

main = xmonad =<< xmobar desktopConfig
  { modMask = mod4Mask
  , terminal = "emacs"
  -- ...
  }