XMonad

xmonad is a tiling window manager for X. Windows are arranged automatically to tile the screen without gaps or overlap, maximizing screen use. Window manager features are accessible from the keyboard: a mouse is optional.

xmonad is written, configured and extensible in Haskell. Custom layout algorithms, key bindings and other extensions may be written by the user in configuration files.

Layouts are applied dynamically, and different layouts may be used on each workspace. Xinerama is fully supported, allowing windows to be tiled on several physical screens.

Installation

The simplest way to install Xmonad is to activate the corresponding NixOS module. You can do this by adding the following to your NixOS configuration. You probably also want to activate the enableContribAndExtras option.

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

The second options automatically adds the xmonad-contrib and xmonad-extras packages. They are required to use the Xmonad Contrib extensions.

To add Haskell modules that are not included in the Xmonad-Contrib package, you have to tell ghc where to find them. For example, you can use the following to add the [1] module.

{ xmonad-contexts, ... }:
{
...
  services.xserver.windowManager.xmonad = {
    ...
    ghcArgs = [
      "-hidir /tmp" # place interface files in /tmp, otherwise ghc tries to write them to the nix store
      "-odir /tmp" # place object files in /tmp, otherwise ghc tries to write them to the nix store
      "-i${xmonad-contexts}" # tell ghc to search in the respective nix store path for the module
    ];
  };
}

Don't forget to add the module to your inputs:

inputs.xmonad-contexts = {
  url = "github:Procrat/xmonad-contexts";
  flake = false;
};

Configuration

To configure Xmonad you give Nix your config file like this:

services.xserver.windowManager.xmonad.config = builtins.readFile ../path/to/xmonad.hs;

More information on how to configure Xmonad can be found in the Arch Wiki, and a list of starter configs can be found in the Xmonad Config Archive.

Power management

Xmonad is a Window Manager (WM) and not a Desktop Environment (DE). Therefore, among other things, Xmonad does not handle power management related things such as sleeping. However, there are several ways of still adding this functionality.

Suspend system after inactivity

The approach goes through the following steps:

Let the XServer detect idle-situation
Inform "logind" (i.e. "systemd") about the situation
Let "logind" make the system sleep

We'll configure the XServers screensaver-settings to pick up inactivity:

/etc/nixos/configuration.nix

  services.xserver.displayManager.sessionCommands = ''
    xset -dpms  # Disable Energy Star, as we are going to suspend anyway and it may hide "success" on that
    xset s blank # `noblank` may be useful for debugging 
    xset s 300 # seconds
    ${pkgs.lightlocker}/bin/light-locker --idle-hint &
  '';

You'll have to re-login for the settings above to be applied.

The settings above will toggle the flag "IdleHint" within logind through light-locker (will work with "'lightdm'", there are alternatives). Next we'll have to pick-up the information within logindand select an action to take:

/etc/nixos/configuration.nix

  systemd.targets.hybrid-sleep.enable = true;
  services.logind.extraConfig = ''
    IdleAction=hybrid-sleep
    IdleActionSec=20s
  '';

The configuration above will let the system go to "hybrid-sleep" `20s` after the screen-saver triggered.

Troubleshooting

Check if the values of "IdleSinceHint" and "IdleSinceHintMonotonic" update using the command:

$ watch "loginctl show-session | grep Idle"

Try setting the flag manually (also need to disable manually):

$ dbus-send --system --print-reply \
    --dest=org.freedesktop.login1 /org/freedesktop/login1/session/self \
    "org.freedesktop.login1.Session.SetIdleHint" boolean:true

Check if the xset-settings have been applied properly and activate the screensaver manually:

$ xset q
$ sleep 1s && xset s activate

Developer Environment for XMonad

When developing modules for XMonad, it can help to install the following packages

windowManager = {
  xmonad = {
    enable = true;
    enableContribAndExtras = true;
    extraPackages = haskellPackages: [
      haskellPackages.dbus
      haskellPackages.List
      haskellPackages.monad-logger
    ];
  };
};

More information can be found here and here.

Create a project around `xmonad.hs`

echo "xmonad" >> $HIE_BIOS_OUTPUT

~/.config/xmonad/hie.yaml

cradle:
  bios:
    program: "./hie-bios.sh"
    with-ghc: "/nix/store/waa0dlvlszwbplrz5c7j674ab6v1n5wi-ghc-8.8.4-with-packages/bin/ghc"

The "with-ghc" should be ghc that's in the "ghc-with-packages" dependency of the "xmonad-with-packages". It can be easily found with "nix-tree", which shows dependencies between packages on the machine.