-- Hoogle documentation, generated by Haddock
-- See Hoogle, http://www.haskell.org/hoogle/


-- | Encapsulating mutatable state in external libraries
--   
@package foreign-var
@version 0


module Foreign.Var

-- | This data type represents a piece of mutable, imperative state with
--   possible side-effects. These tend to encapsulate all sorts tricky
--   behavior in external libraries, and may well throw exceptions.
--   
--   Inhabitants <b>should</b> satsify the following properties.
--   
--   In the absence of concurrent mutation from other threads or a thrown
--   exception:
--   
--   <pre>
--   do x &lt;- <a>getVar</a> v; <a>setVar</a> v y; <a>setVar</a> v x
--   </pre>
--   
--   should restore the previous state.
--   
--   Ideally, in the absence of thrown exceptions:
--   
--   <pre>
--   <a>setVar</a> v a &gt;&gt; <a>getVar</a> v
--   </pre>
--   
--   should return <tt>a</tt>, regardless of <tt>a</tt>. In practice some
--   <a>Var</a>s only permit a very limited range of value assignments, and
--   do not report failure.
--   
--   The result of <a>updateVar</a> should also be compatible with the
--   result of getting and setting separately, however, it may be more
--   efficient or have better atomicity properties in a concurrent setting.
data Var a
Var :: IO a -> ((a -> a) -> IO ()) -> ((a -> a) -> IO ()) -> (a -> IO ()) -> Var a

-- | Used by <a>get</a>
getVar :: Var a -> IO a

-- | Used by <tt>(<a>$~</a>)</tt>
updateVar :: Var a -> (a -> a) -> IO ()

-- | Used by <tt>(<a>$~!</a>)</tt>
updateVar' :: Var a -> (a -> a) -> IO ()

-- | Used by <tt>(<a>$=</a>)</tt>
setVar :: Var a -> a -> IO ()

-- | Build a <a>Var</a> form a getter and a setter.
newVar :: (IO a) -> (a -> IO ()) -> Var a

-- | Change the type of a <a>Var</a>
mapVar :: (b -> a) -> (a -> b) -> Var a -> Var b
newtype SettableVar a
SettableVar :: (a -> IO ()) -> SettableVar a
type GettableVar = IO
class HasSetter t a | t -> a
($=) :: (HasSetter t a, MonadIO m) => t -> a -> m ()
($=!) :: (HasSetter t a, MonadIO m) => t -> a -> m ()
class HasSetter t a => HasUpdate t a b | t -> a b where r $~ f = liftIO $ do { a <- get r; r $= f a } r $~! f = liftIO $ do { a <- get r; r $=! f a }
($~) :: (HasUpdate t a b, MonadIO m) => t -> (a -> b) -> m ()
($~!) :: (HasUpdate t a b, MonadIO m) => t -> (a -> b) -> m ()
class HasGetter t a | t -> a
get :: (HasGetter t a, MonadIO m) => t -> m a
instance Typeable Var
instance Typeable SettableVar
instance HasGetter (IORef a) a
instance Storable a => HasGetter (Ptr a) a
instance HasGetter (STM a) a
instance HasGetter (IO a) a
instance HasGetter (TVar a) a
instance HasGetter (Var a) a
instance HasUpdate (TVar a) a a
instance HasUpdate (IORef a) a a
instance Storable a => HasUpdate (Ptr a) a a
instance HasUpdate (Var a) a a
instance HasSetter (TVar a) a
instance HasSetter (IORef a) a
instance Storable a => HasSetter (Ptr a) a
instance HasSetter (Var a) a
instance HasSetter (SettableVar a) a