I actually started hacking on a Prolog X11 WM last year, got distracted by other things but what I started with was a module to define BSP-style partitions usin

I actually started hacking on a Prolog X11 WM last year, got distracted by other things but what I started with was a module to define BSP-style partitions using rational constraints, so you would be able e.g. to easily cycle between valid pane layouts.