Excerpts from Mike Meyer's message of 2014-09-23 07:31:08 -0700:
The Message is called "SplitMaster", and has no arguments. It sets the client count of the master pane to 1 if it's not currently 1, thus providing a quick way to get back to that setting. It setgs the client count for the master pane to 2 if it's currently 1, effectively making it a toggle between the two modes of a split master pane and an full size master pane.
Can this be done entirely from the configuration? For example, a low-tech solution would be to simply have two Tall layouts in your layout hook (one with one master pane and one with two master panes) and a keybinding that toggles between them, e.g. using X.A.CycleSelectedLayouts [1]. I recognize that this is not *identical*, but perhaps it's close to your needs and doesn't require changes xmonad's core. ~d [1] http://hackage.haskell.org/package/xmonad-contrib-0.11.3/docs/XMonad-Actions...