libghc-xmonad-dev 0.15-1build3 (armhf binary) in ubuntu focal

 Xmonad is a minimalist tiling window manager for X, written in
 Haskell. Windows are managed using automatic layout algorithms,
 which can be dynamically reconfigured. At any time windows are
 arranged so as to maximise the use of screen real estate. All
 features of the window manager are accessible purely from the
 keyboard: a mouse is entirely optional. Xmonad is configured in
 Haskell, and custom layout algorithms may be implemented by the user
 in config files. A principle of Xmonad is predictability: the user
 should know in advance precisely the window arrangement that will
 result from any action.
 .
 This package is what you need to build your custom configured xmonad
 binary.
 .
 This package provides a library for the Haskell programming language.
 See http://www.haskell.org/ for more information on Haskell.