[xmonad] run a program when switching to a workspace

[Brent Yorgey]

On Thu, May 28, 2009 at 10:50:34AM +0300, Roman Cheplyaka wrote:
> * Brent Yorgey <byorgey at seas.upenn.edu> [2009-05-27 22:52:04-0400]
> > On Mon, May 25, 2009 at 08:47:42AM -0600, Sergey Manucharian wrote:
> > > Hi folks,
> > > 
> > > How can I configure xmonad to run a program when switching to a
> > > particular workspace? Example: I want to run a script changing the
> > > keyboard layout to "us" unconditionally when I'm on particular
> > > workspaces (with ssh, rdesktop etc.).
> > 
> > The easiest way to do this is to add an action to your logHook that
> > checks the current workspace, and sets the keyboard layout if it is
> > the desired workspace:
> >  
> >   ...
> >   logHook = ...other stuff... >> checkKBLayout
> > 
> >   ...
> > 
> >   checkKBLayout :: X ()
> >   checkKBLayout = do
> >     curTag <- gets (W.currentTag . windowset)
> >     when (curTag == "foo") $ spawn "set keyboard layout"
> > 
> > Of course, "foo" should be replaced with whatever workspace you want,
> > and "set keyboard layout" should be replaced with a suitable command
> > for setting the keyboard layout.
> 
> Just to make it clear: the command will be spawned each time when
> windowset changes -- e.g. when you change the focus. It's harmless with
> setting kb layout, but if you use it for e.g. launching an application
> you'll get a new instance each time you change focus.
> 
> Another possibility is to create IORef and store previous workspace
> there, so you can know whether you really _switched_ to current
> workspace.
> 
> Maybe create a layer on top of logHook which would provide incremental
> information?

That's a nice idea!  I've always thought that the logHook could be
generalized in a number of interesting ways.  There are lots of things
that might want to be notified of status changes which have nothing to
do with logging.

-Brent