[Xmonad] Tiled layout with more columns?

[Kai Grossjohann]

I've got a widescreen display and I found out that three columns of
windows fit comfortably.  So I would be interested in a layout that is
similar to the normal¹ tiled layout, except that it has three columns
instead of two.

The first window would go in the master area, then half of the remaining
windows would go into the middle column, the other half of in the
rightmost column.  (The rightmost column may have one more window than
the middle column, depending on the number of windows in the workspace.)

The middle column and the right column would have the same width.

Does something like this exist already?

tia,
Kai