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-- |
-- Module      :  Graphics.Rendering.OpenGL.GL.StateVar
-- Copyright   :  (c) Sven Panne 2002-2006
-- License     :  BSD-style (see the file libraries/OpenGL/LICENSE)
-- 
-- Maintainer  :  [email protected]
-- Stability   :  stable
-- Portability :  portable
--
--------------------------------------------------------------------------------

module Graphics.Rendering.OpenGL.GL.StateVar (
   HasGetter(..),
   GettableStateVar, makeGettableStateVar,
   HasSetter(..), set,
   SettableStateVar, makeSettableStateVar,
   StateVar, makeStateVar,
   ($~), ($=!), ($~!)
) where

import Data.IORef ( IORef, readIORef, writeIORef )

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infixr 2 $=

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class HasGetter g where
   get :: g a -> IO a

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newtype GettableStateVar a = GettableStateVar (IO a)

instance HasGetter GettableStateVar where
   get (GettableStateVar g) = g

makeGettableStateVar :: IO a -> GettableStateVar a
makeGettableStateVar = GettableStateVar

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class HasSetter s where
   ($=) :: s a -> a -> IO ()

{-# DEPRECATED set "use `sequence_' instead" #-}
set :: [IO ()] -> IO ()
set = sequence_

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newtype SettableStateVar a = SettableStateVar (a -> IO ())

instance HasSetter SettableStateVar where
   ($=) (SettableStateVar s) a = s a

-- | A strict variant of '$='.
($=!) :: HasSetter s => s a -> a -> IO ()
v $=! x = x `seq` v $= x

makeSettableStateVar :: (a -> IO ()) -> SettableStateVar a
makeSettableStateVar = SettableStateVar

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data StateVar a =
   StateVar (GettableStateVar a) (SettableStateVar a)

instance HasGetter StateVar where
   get (StateVar g _) = get g

instance HasSetter StateVar where
   ($=) (StateVar _ s) a = s $= a

makeStateVar :: IO a -> (a -> IO ()) -> StateVar a
makeStateVar g s = StateVar (makeGettableStateVar g) (makeSettableStateVar s)

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-- | A modificator convenience function.

($~) :: (HasGetter v, HasSetter v) => v a -> (a -> a) -> IO ()
v $~ f = do
   x <- get v
   v $= f x

-- | A strict variant of '$~'.
($~!) :: (HasGetter v, HasSetter v) => v a -> (a -> a) -> IO ()
v $~! f = do
   x <- get v
   v $=! f x

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instance HasGetter IORef where
   get = readIORef

instance HasSetter IORef where
   ($=) = writeIORef