[xmonad] ppVisible with 3 screens

[Norbert Zeh]

Felix Blanke [2010.10.10 1046 +0200]:
> Hi,
> 
> are you sure that it doesn't work with only one screen?

Your are right here.  This function will work on single screen, even
though it won't do what you want (the first invisible screen would be
the one listed first).  However, Adam is right to the point that the
pattern match of "prm" *can* fail under some circumstances, namely when
you run this with less than two workspaces.  This, however, would be a
change in your xmonad.hs, and that means you should inspect everything
else in your setup for correctness anyway.

Cheers,
Norbert

> 
> Even with only one screen "getSortByXineramaRule" returns a list with 9 workspaces
> (I'm using 9 workspaces) in it, right? Logicaly the sorting after the let is wrong
> then, but there should be no error.
> 
> But like I said: I'm a haskell noob, maybe I'm totaly wrong :)
> 
> 
> How would I add that fallback? You wrote some ], but I'm not sure how such a fallback
> looks @haskell
> 
> myXineramaSorter = do
>     srt <- getSortByXineramaRule
>     let prm (one:two:rest) = two:one:rest
>     return (prm . srt)
> 
> 
> Felix
> 
> 
> 
> On 09. October 2010 - 20:18, Adam Vogt wrote:
> > Date: Sat, 9 Oct 2010 20:18:58 -0400
> > From: Adam Vogt <vogt.adam at gmail.com>
> > To: xmonad at haskell.org
> > Subject: Re: [xmonad] ppVisible with 3 screens
> > 
> > * On Friday, October 08 2010, Felix Blanke wrote:
> > 
> > >Hello,
> > >
> > >thanks a lot for your work!
> > >
> > >
> > >It works :) The short version
> > >
> > >"let prm (one:two:rest) = two:one:rest"
> > >
> > >is enough, because I only need to switch the first two elements.
> > >With this hack I don't need the colour thing.
> > >
> > >
> > >Thanks again!
> > >
> > >
> > >Regards,
> > >Felix
> > 
> > If you end up using that config with only one screen, that expression
> > will throw an exception. XMonad will most likely catch it, but the
> > recovery is to try again. Arguably xmonad should do something smarter,
> > but until something changes there, you'd get an infinite loop.
> > 
> > So add a fallback case to the definition:
> > 
> > ] let prm (one:two:rest) = two:one:rest
> > ]     prm x = x
> > 
> > --
> > Adam
> > _______________________________________________
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> > xmonad at haskell.org
> > http://www.haskell.org/mailman/listinfo/xmonad
> ---end quoted text---
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