atrans 0.1.0.1 → 0.1.1.0

raw patch · 2 files changed

+17/−9 lines, 2 filesPVP: major bump suggested

API removals or changes: PVP suggests a major version bump

API changes (from Hackage documentation)

Files

• atrans.cabal +1/−1
• src/Control/Monad/Backend.hs +16/−8

@@ -1,5 +1,5 @@ name:                atrans-version:             0.1.0.1+version:             0.1.1.0 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

@@ -16,27 +16,35 @@  import Control.Monad.Except import Control.Monad.State-import Control.Concurrent.MVar (MVar, isEmptyMVar, modifyMVar_, takeMVar, putMVar, readMVar)+import Control.Concurrent.MVar (MVar, isEmptyMVar, modifyMVar_, takeMVar, putMVar, readMVar, newMVar) import Control.Arrow (second)  --- | 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.+{-| The 'BackendT' transformer is a 'StateT', where the state is encapsulated into a 'MVar'. We have++    BackendT s m a++where `s` is the state and `m` is a monad, usually with a 'MonadIO' constraint. The state is only unwrapped, when 'get', 'set' or 'state' is used. A 'bind' will not unwrap.  -} newtype BackendT s m a = BackendT (MVar s -> m (MVar s, a)) --- | 'runBackendT' unwraps the 'BackendT' monad.-runBackendT :: BackendT s m a -> MVar s -> m (MVar s, a)-runBackendT (BackendT f) = f+-- | 'runBackendT' unwraps the 'BackendT' monad on a given initial state. This given state is wrapped into an 'MVar'.+runBackendT :: (Monad m, MonadIO m) => BackendT s m a -> s -> m (MVar s, a)+runBackendT (BackendT f) s = do { v <- liftIO (newMVar s); f v } +-- | 'rawRunBackendT' unwraps then 'BackendT' monad on a given initial state, where this state is wrapped into an 'MVar'. **The 'MVar' shouldn't be empty, otherwise every state reading/writing is blocking.** Usually, one should use 'runBackendT'.+rawRunBackendT :: BackendT s m a -> MVar s -> m (MVar s, a)+rawRunBackendT (BackendT f) = f+ instance (Functor m) => Functor (BackendT s m) where-  fmap f bt = BackendT $ \s -> fmap (second f) (runBackendT bt s)+  fmap f bt = BackendT $ \s -> fmap (second f) (rawRunBackendT bt s)  instance (Monad m) => Applicative (BackendT s m) where   pure x = BackendT $ \s -> pure (s, x)-  pf <*> q = BackendT $ \s -> do { (s', f) <- runBackendT pf s; (s'', x) <- runBackendT q s'; return (s'', f x) }+  pf <*> q = BackendT $ \s -> do { (s', f) <- rawRunBackendT pf s; (s'', x) <- rawRunBackendT q s'; return (s'', f x) }  instance (Monad m) => Monad (BackendT s m) where   return x = BackendT $ \s -> return (s, x)-  p >>= (fq) = BackendT $ \s -> do { (s', x) <- runBackendT p s; runBackendT (fq x) s' }+  p >>= fq = BackendT $ \s -> do { (s', x) <- rawRunBackendT p s; rawRunBackendT (fq x) s' }  instance (Monad m, MonadIO m) => MonadState s (BackendT s m) where   get = BackendT $ \s -> do { v <- liftIO (readMVar s); return (s, v) }