[Xmonad] Issue 78 in xmonad: Extension state

[Don Stewart]

codesite-noreply:
> Issue 78: Extension state
> http://code.google.com/p/xmonad/issues/detail?id=78
> 
> Comment #1 by daveroundy:
> Note, we could also make other hooks use the same mechanism as
> Layouts.  The Layout mechanism is similar in effect to a writer monad,
> but with a special-case for when the state doesn't change, so we won't
> have to redraw the windows if a message doesn't change the layout.
> This approach seems to work well for Layouts, but I suppose isn't
> needed for other hooks (as we don't care whether or not they've
> changed).  It also make it pretty easy to write buggy layout
> combinators, since it's all too easy to ignore that return value.

That's interesting!
  
> I wonder if perhaps a custom monad would be helpful for Layouts? And
> whether perhaps we could use a similar approach for hooks? i.e. if we
> put hooks into a monad that allows them to return a modified hook,
> wouldn't that be enough?

If we moved to a monadic model for private state, I would imaging 
we'd move the layouts over to that as well.

-- Don