A decoration that allows to switch the position of windows by dragging them onto each other.

You can use this module with the following in your ~/.xmonad/xmonad.hs:

import XMonad.Layout.WindowSwitcherDecoration
import XMonad.Layout.DraggingVisualizer

Then edit your layoutHook by adding the WindowSwitcherDecoration to your layout:

myL = windowSwitcherDecoration shrinkText def (draggingVisualizer $ layoutHook def)
main = xmonad def { layoutHook = myL }

There is also a version of the decoration that contains buttons like XMonad.Layout.ButtonDecoration. To use that version, you will need to import XMonad.Layout.DecorationAddons as well and modify your layoutHook in the following way:

import XMonad.Layout.DecorationAddons

myL = windowSwitcherDecorationWithButtons shrinkText defaultThemeWithButtons (draggingVisualizer $ layoutHook def)
main = xmonad def { layoutHook = myL }

Additionaly, there is a version of the decoration that contains image buttons like XMonad.Layout.ImageButtonDecoration. To use that version, you will need to import XMonad.Layout.ImageButtonDecoration as well and modify your layoutHook in the following way:

import XMonad.Layout.ImageButtonDecoration

myL = windowSwitcherDecorationWithImageButtons shrinkText defaultThemeWithImageButtons (draggingVisualizer $ layoutHook def)
main = xmonad def { layoutHook = myL }