[Xmonad] Rotate window Stack

[Donald Bruce Stewart]

hpa:
> Hello List, 
> 
> I just recently found out about xmonad and I am addicted already :)
> Thanks for this great window manager.
> 
> I have written a function that will rotate all windows in the stack
> except the master, while leaving the focus where it is.
> I use it with the TwoPane layout: In this layout, the first window after
> the master window will be raised whenever the master gets the focus,
> which I found annoying. 
> If that window has the focus, and you use my rotateSlaves function to
> change to another window, this window will still be visible when you
> change the focus to the master window.
> It is also nice to be able to change the window visible in the second
> pane without loosing focus in the master window.

Ii think this is a nice idea, and should definitely go in the contrib
module. We want to keep the core api very small, and just let people
pick and choose their extensions.

> I was not sure whether I should put this in XMonadContrib, since I think
> it's a candidate for Operations.hs.
> 
> Anyway, here is the function:
> 
> 
> rotSlaves :: SS.StackSet i a s sd -> SS.StackSet i a s sd
> rotSlaves = SS.modify' rotSlaves'
> 
> rotSlaves' :: SS.Stack a -> SS.Stack a
> rotSlaves' (SS.Stack t ls rs) | (null ls) = SS.Stack t [] ((rearRs)++(frontRs))          --Master has focus
>                               | otherwise = SS.Stack t' (reverse ((master)++revls')) rs' --otherwise
>     where  (frontRs, rearRs) = splitAt (max 0 ((length rs) - 1) rs
>            (ils, master)     = splitAt (max 0 ((length ls) - 1) ls
>            toBeRotated       = (reverse ils)++(t:rs)
>            (revls',t':rs')   = splitAt (length ils) ((last toBeRotated):(init toBeRotated))
> 
> 
> a keybinding looks like:
> 
>   , ((modMask .|. shiftMask, xK_Tab   ), windows rotSlaves) 
> 
> 
> 
> I hope someone else will find that usefull...

Nice, feel free to submit it as a contrib module (and perhaps with some
internal quickcheck properties to  ensure the invariant that the master
doesn't move, and that focus is kept where it starts. (have a look in
tests/Properties.hs for example QC tests for this kind of thing).

-- Don