Re: [xmonad] The future of PerWorkspace

On Fri, Feb 1, 2008 at 5:04 PM, Nicolas Pouillard < nicolas.pouillard@gmail.com> wrote:

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On Thu, Jan 31, 2008 at 2:42 PM, Spencer Janssen wrote:

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On Wed, Jan 30, 2008 at 07:29:58PM -0500, Brent Yorgey wrote:

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1. PerWorkspace is an inelegant hack with several icky problems:

Agreed. It is approaching the limits of xmonad's layout design. However, I think we can accomplish PerWorkspace behavior without changing too much.

\begin{code} data PerWS = PerWS { selected :: Maybe Layout , choices :: Map WorkspaceId Layout , default :: Layout } \end{code}

So, I took a crack at implementing (something like) this today. The

Excerpts from Brent Yorgey's message of Fri Feb 01 22:53:20 +0100 2008: problem

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I ran into is that (Layout a) is not an instance of Read, so PerWorkspace cannot derive Read either. Is there any way around this? Or do I have to go back to caching a (Maybe Bool) and using that to decide on which of two layouts to use, instead of directly caching a (Maybe (Layout a))?

Ideas?

What about "instance Read a => Read (Layout a)"?

Well, since Layout is an existential wrapper, that's not possible -- it hides the type of the wrapped layout. I know that lots of work has already gone into the xmonad core getting around this issue. =) Hmm, just thinking out loud here... note that I don't actually care about being able to read the (Layout a) value back in, since after serialization/restart the startupHook will get run again anyway, and the correct workspace will get re-cached. So perhaps I can just write my own explicit Read instance for PerWorkspace that somehow ignores that element and just initializes the read value to Nothing. Sounds scary. =) -Brent