atrans 0.1.0.0 → 0.1.0.1

raw patch · 2 files changed

+9/−6 lines, 2 filesPVP ok

version bump matches the API change (PVP)

API changes (from Hackage documentation)

Files

• atrans.cabal +1/−1
• src/Control/Monad/Backend.hs +8/−5

@@ -1,5 +1,5 @@ name:                atrans-version:             0.1.0.0+version:             0.1.0.1 synopsis:            A small collection of monad (transformer) instances. description:         Defines monad transformers and gives instances based on the mtl transformer library. homepage:            https://github.com/aphorisme/atrans

@@ -16,11 +16,11 @@  import Control.Monad.Except import Control.Monad.State-import Control.Concurrent.MVar (MVar, isEmptyMVar, takeMVar, putMVar, readMVar)+import Control.Concurrent.MVar (MVar, isEmptyMVar, modifyMVar_, takeMVar, putMVar, readMVar) import Control.Arrow (second)  --- | The 'BackendT' transformer is a 'StateT', where the state is encapsulated into a 'MVar'.+-- | The 'BackendT' transformer is a 'StateT', where the state is encapsulated into a 'MVar'. The initialized 'MVar' has to be non empty, otherwise every state change is blocking. newtype BackendT s m a = BackendT (MVar s -> m (MVar s, a))  -- | 'runBackendT' unwraps the 'BackendT' monad.@@ -41,9 +41,12 @@ instance (Monad m, MonadIO m) => MonadState s (BackendT s m) where   get = BackendT $ \s -> do { v <- liftIO (readMVar s); return (s, v) }   put s = BackendT $-    \st -> do b <- liftIO (isEmptyMVar st)-              if b then do { liftIO (putMVar st s); return (st, ()) }-              else do { liftIO (takeMVar st); liftIO (putMVar st s); return (st, ()) }+    \st -> do { liftIO (modifyMVar_ st (\_ -> return s)); return (st, ()) }+  state f = BackendT $+    \ms -> do s <- liftIO (takeMVar ms)+              let (x, s') = f s+              liftIO (putMVar ms s')+              return (ms, x)  instance (Monad m, MonadIO m) => MonadIO (BackendT s m) where   liftIO io = BackendT $ \s -> do { x <- liftIO io; return (s, x) }