From 795fed842c57d980e7644bb2df9eb66078ae6d44 Mon Sep 17 00:00:00 2001
From: Daniel Schoepe <daniel.schoepe@gmail.com>
Date: Fri, 6 Nov 2009 12:50:50 +0100
Subject: Support for extensible state in contrib modules.

Ignore-this: d04ee1989313ed5710c94f9d7fda3f2a

darcs-hash:20091106115050-7f603-c88ce5e468856afd9e4d458ed3b0a2cfa39e63b3.gz
---
 XMonad/Core.hs | 46 +++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 39 insertions(+), 7 deletions(-)

(limited to 'XMonad/Core.hs')

diff --git a/XMonad/Core.hs b/XMonad/Core.hs
index 1b7b70a..23394f6 100644
--- a/XMonad/Core.hs
+++ b/XMonad/Core.hs
@@ -24,6 +24,7 @@ module XMonad.Core (
     XConf(..), XConfig(..), LayoutClass(..),
     Layout(..), readsLayout, Typeable, Message,
     SomeMessage(..), fromMessage, LayoutMessages(..),
+    StateExtension(..), ExtensionClass(..),
     runX, catchX, userCode, userCodeDef, io, catchIO, installSignalHandlers, uninstallSignalHandlers,
     withDisplay, withWindowSet, isRoot, runOnWorkspaces,
     getAtom, spawn, spawnPID, getXMonadDir, recompile, trace, whenJust, whenX,
@@ -51,20 +52,24 @@ import Graphics.X11.Xlib
 import Graphics.X11.Xlib.Extras (Event)
 import Data.Typeable
 import Data.List ((\\))
-import Data.Maybe (isJust)
+import Data.Maybe (isJust,fromMaybe)
 import Data.Monoid
-import Data.Maybe (fromMaybe)
 
 import qualified Data.Map as M
 import qualified Data.Set as S
 
 -- | XState, the (mutable) window manager state.
 data XState = XState
-    { windowset    :: !WindowSet           -- ^ workspace list
-    , mapped       :: !(S.Set Window)      -- ^ the Set of mapped windows
-    , waitingUnmap :: !(M.Map Window Int)  -- ^ the number of expected UnmapEvents
-    , dragging     :: !(Maybe (Position -> Position -> X (), X ())) }
-
+    { windowset        :: !WindowSet                     -- ^ workspace list
+    , mapped           :: !(S.Set Window)                -- ^ the Set of mapped windows
+    , waitingUnmap     :: !(M.Map Window Int)            -- ^ the number of expected UnmapEvents
+    , dragging         :: !(Maybe (Position -> Position -> X (), X ()))
+    , extensibleState  :: !(M.Map String (Either String StateExtension))
+    -- ^ stores custom state information.
+    --
+    -- The module XMonad.Utils.ExtensibleState in xmonad-contrib
+    -- provides additional information and a simple interface for using this.
+    }
 -- | XConf, the (read-only) window manager configuration.
 data XConf = XConf
     { display       :: Display        -- ^ the X11 display
@@ -343,6 +348,33 @@ data LayoutMessages = Hide              -- ^ sent when a layout becomes non-visi
 
 instance Message LayoutMessages
 
+-- ---------------------------------------------------------------------
+-- Extensible state
+--
+
+-- | Every module must make the data it wants to store
+-- an instance of this class.
+--
+-- Minimal complete definition: initialValue
+class Typeable a => ExtensionClass a where
+    -- | Defines an initial value for the state extension
+    initialValue :: a
+    -- | Specifies whether the state extension should be
+    -- persistent. Setting this method to 'PersistentExtension'
+    -- will make the stored data survive restarts, but
+    -- requires a to be an instance of Read and Show.
+    --
+    -- It defaults to 'StateExtension', i.e. no persistence.
+    extensionType :: a -> StateExtension
+    extensionType = StateExtension
+
+-- | Existential type to store a state extension.
+data StateExtension =
+    forall a. ExtensionClass a => StateExtension a
+    -- ^ Non-persistent state extension
+  | forall a. (Read a, Show a, ExtensionClass a) => PersistentExtension a
+    -- ^ Persistent extension
+
 -- ---------------------------------------------------------------------
 -- | General utilities
 --
-- 
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