Maybe try removing the ~/.xmonad/xmonad.o and ~/.xmonad/xmonad.hi files – I’d be surprised to see that libghc6-xmonad-dev depend on libghc6-x11-dev (= 1.4.2-1) but be built against X11-1.4.1.
Also note that newer pakages are in Debian, maybe they can be merged.
Maybe try removing the ~/.xmonad/xmonad.o and ~/.xmonad/xmonad.hi files – I’d be surprised to see that libghc6-xmonad-dev depend on libghc6-x11-dev (= 1.4.2-1) but be built against X11-1.4.1.
Also note that newer pakages are in Debian, maybe they can be merged.