[xmonad] darcs patch: XMonad.Config.Prime, a do-notation for config

adam vogt vogt.adam at gmail.com
Wed Mar 13 05:26:47 CET 2013

On Tue, Mar 12, 2013 at 5:30 AM,  <me at twifkak.com> wrote:
> Hello, folks,
> It's me again. First off, I see that you released 0.11 in Dec. Nice! Second, I
> took some time to take another crack at this config thing. (Previous thread:
> http://www.haskell.org/pipermail/xmonad/2012-September/013045.html.)
> Because of the problems you guys mentioned with Template Haskell, I:
> 1. replaced the fclabels dependency with the lighter data-accessor.
> 2. replaced the StateT with a fake monad, so the type of the layoutHook can be
>    changed without that existential mess.
> The upside is an even cleaner syntax. The downside is:
> 1. You have to come to terms with having RebindableSyntax in your xmonad.hs.
> 2. Error messages are uglier (thanks, in part, to the really long layout types).
> Docs at: http://twifkak.com/xmonad-junk/XMonad-Config-Prime2.html
> Thoughts?
> Devin

Hi Devin,

Regarding the "TODO: Figure out how to type this without hard-coding
the defaultConfig layout type.", maybe something is possible with

xmonad :: (Read (l Window), LayoutClass l Window) => (forall l0.
(Read (l0 Window), LayoutClass l0 Window) => XConfig l0 -> IO (XConfig
l)) -> IO ()

But that only seems to work when prime includes a resetLayout, since
the `l' isn't allowed to refer to the `l0'. It's still possible to
write a type signature for XMonad.Config.Prime.xmonad, but since we
aren't likely to change the type of defaultConfig anytime soon it's
fine as-is.

Some configs use do notation for IO in main before calling xmonad, or
possibly for sequencing multiple X actions that are supposed to happen
with a single keybinding. Enabling -XRebindableSyntax looks like it
would force people to use a qualified name like Prelude.>>=, or put
the definitions in separate modules. The second option is not
necessarily a bad thing.

Maybe it's possible to write a class with a >>= and >> that can work
with IO or Prime, but that probably will make type errors even worse.


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