nixos/xmonad: move to haskell-ng and make a wrapper

pkgs/applications/window-managers/xmonad/wrapper.nix

@@ -0,0 +1,22 @@
+{ stdenv, buildEnv, ghcWithPackages, xmessage, makeWrapper, packages }:
+
+let
+xmonadEnv = ghcWithPackages (self: [ self.xmonad ] ++ packages self);
+drv = buildEnv {
+  name = "xmonad-with-packages";
+
+  paths = [ xmonadEnv ];
+
+  postBuild = ''
+    # TODO: This could be avoided if buildEnv could be forced to create all directories
+    rm $out/bin
+    mkdir $out/bin
+    for i in ${xmonadEnv}/bin/*; do
+      ln -s $i $out/bin
+    done
+    wrapProgram $out/bin/xmonad \
+      --set XMONAD_GHC "${xmonadEnv}/bin/ghc" \
+      --set XMONAD_XMESSAGE "${xmessage}/bin/xmessage"
+  '';
+  };
+in stdenv.lib.overrideDerivation drv (x : { buildInputs = x.buildInputs ++ [ makeWrapper ]; })