jwm: window manager module addition

nixos/modules/services/x11/window-managers/default.nix

@@ -17,6 +17,7 @@ in
     ./fluxbox.nix
     ./herbstluftwm.nix
     ./i3.nix
+    ./jwm.nix
     ./metacity.nix
     ./openbox.nix
     ./notion.nix

nixos/modules/services/x11/window-managers/jwm.nix

@@ -0,0 +1,25 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.services.xserver.windowManager.jwm;
+in
+{
+  ###### interface
+  options = {
+    services.xserver.windowManager.jwm.enable = mkEnableOption "jwm";
+  };
+
+  ###### implementation
+  config = mkIf cfg.enable {
+    services.xserver.windowManager.session = singleton {
+      name = "jwm";
+      start = ''
+        ${pkgs.jwm}/bin/jwm &
+        waitPID=$!
+      '';
+    };
+    environment.systemPackages = [ pkgs.jwm ];
+  };
+}