Thanks again guys. I had some trouble with cabal-install dependencies on Mint, but would prefer stable packages anyway. Mint/Mate is now stable as long as I'm willing to start with 'xmonad --replace &' in a terminal after login. Xmonad from XDG/Login might be possible (with first two files below) if I start up a session manager and a bunch of utilities (in third file); I haven't tried. I would like to try with LXDE.
# apt-get install xmonad libghc-xmonad-contrib-dev libghc-xmonad-dev
==> /usr/share/xsessions/xmonad.desktop <==
[Desktop Entry]
Name=XMonad
Comment=Lightweight tiling window manager
Exec=xmonad.start
Icon=xmonad.png
Type=XSession
==> /usr/share/applications/xmonad.start.desktop <==
[Desktop Entry]
Type=Application
Name=Xmonad
Exec=/usr/local/bin/xmonad.start
NoDisplay=true
X-GNOME-WMName=Xmonad
X-GNOME-Autostart-Phase=WindowManager
X-GNOME-Provides=windowmanager
X-GNOME-Autostart-Notify=true
==> /usr/local/bin/xmonad.start <==
#!/bin/bash
#mate-panel &
exec xmonad
==> xmonad.hs <==
import XMonad
import XMonad.Config.Desktop
main = xmonad $ desktopConfig {
modMask = mod4Mask
, terminal = "mate-terminal"
}