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{-# LANGUAGE DeriveDataTypeable #-}
-----------------------------------------------------------------------------
-- |
-- Module : XMonad.Util.ExtensibleState
-- Copyright : (c) Spencer Janssen 2009
-- License : BSD3-style (see LICENSE)
--
-- Maintainer : spencerjanssen@gmail.com
-- Stability : unstable
-- Portability : not portable
--
-- A module for spawning a command once, and only once. Useful to start
-- status bars and make session settings inside startupHook.
--
-----------------------------------------------------------------------------
module XMonad.Util.SpawnOnce (spawnOnce) where
import XMonad
import Data.Set as Set
import qualified XMonad.Util.ExtensibleState as XS
import Control.Monad
data SpawnOnce = SpawnOnce { unspawnOnce :: (Set String) }
deriving (Read, Show, Typeable)
instance ExtensionClass SpawnOnce where
initialValue = SpawnOnce Set.empty
extensionType = PersistentExtension
-- | The first time 'spawnOnce' is executed on a particular command, that
-- command is executed. Subsequent invocations for a command do nothing.
spawnOnce :: String -> X ()
spawnOnce xs = do
b <- XS.gets (Set.member xs . unspawnOnce)
when (not b) $ do
spawn xs
XS.modify (SpawnOnce . Set.insert xs . unspawnOnce)
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