User state in Xmonad

Question

Is it possible to have a user state in Xmonad?

I'm using global variables right now, but I wonder if there's a proper way to do it within Xmonad. (Eg: in parsec, there's a user state, so you would use Parser TYPE ... where TYPE is the type of the user state and is queryable with getState, putState, and modifyState.)

Answer 1

Layout states in Xmonad can be specified/modified in the config.hs module, but Xmonad has also got extensible states that you can implement. I would recommend you look at both. The docs on the Haskell Extensible States lists the module as 'unstable' but i think it's a fair while since that documentation was updated (about three years?)

The [sample] code looks something like this:

 {-# LANGUAGE DeriveDataTypeable #-}
import qualified XMonad.Util.ExtensibleState as XS

data ListStorage = ListStorage [Integer] deriving Typeable
instance ExtensionClass ListStorage where
initialValue = ListStorage []

.. XS.put (ListStorage [23,42])

 (e.g.)  put :: ExtensionClass a => a -> X ()