Merge pull request #196 from Ongy/sessionstartup

Add XMonad.Util.SessionStart

XMonad/Util/SessionStart.hs

@@ -0,0 +1,64 @@
+{-# LANGUAGE DeriveDataTypeable #-}
+
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  XMonad.Util.SessionStart
+-- Copyright   :  (c) Markus Ongyerth 2017
+-- License     :  BSD3-style (see LICENSE)
+--
+-- Maintainer  :  markus@ongy.net
+-- Stability   :  unstable
+-- Portability :  not portable
+--
+-- A module for detectiong session startup.  Useful to start
+-- status bars, compositors and session initialization.
+-- This is a more general approach than spawnOnce and allows spawnOn etc.
+-----------------------------------------------------------------------------
+
+module XMonad.Util.SessionStart
+    ( doOnce
+    , isSessionStart
+    , setSessionStarted
+    )
+where
+
+import Control.Monad (when)
+import Control.Applicative ((<$>))
+
+import XMonad
+import qualified XMonad.Util.ExtensibleState as XS
+
+-- ---------------------------------------------------------------------
+-- $usage
+--
+-- Add 'setSessionStarted' at the end of the 'startupHook' to set the
+-- flag.
+--
+-- To do something only when the session is started up, use 
+-- 'isSessionStart' to query or wrap it in 'doOnce' to only do it when
+-- the flag isn't set.
+-- ---------------------------------------------------------------------
+
+data SessionStart = SessionStart { unSessionStart :: Bool }
+    deriving (Read, Show, Typeable)
+
+instance ExtensionClass SessionStart where
+    initialValue = SessionStart True
+    extensionType = PersistentExtension
+
+-- | Use this to only do a part of your hook on session start
+doOnce :: X () -> X ()
+doOnce act = do
+    startup <- isSessionStart
+    when startup act
+
+-- | Query if the current startup is the session start
+isSessionStart :: X Bool
+isSessionStart = unSessionStart <$> XS.get
+
+-- This should become a noop/be deprecated when merged into master, and
+-- the flag should be set when the state file is loaded.
+-- | This currently has to be added to the end of the startup hook to
+-- set the flag.
+setSessionStarted :: X ()
+setSessionStarted = XS.put $ SessionStart False