Control.Monad.IO.Peel · monad-peel-0.3

classclass MonadIO m => MonadPeelIO (m :: Type -> Type) where

MonadPeelIO is the class of IO-based monads supporting an extra operation peelIO, enabling control operations on IO to be lifted into the monad.

Methods

peelIO :: m (m a -> IO (m a))
peelIO is a version of peel that operates through an arbitrary stack of monad transformers directly to an inner IO (analagously to how liftIO is a version of lift). So it can be used with liftIO to lift control operations on IO into any monad in MonadPeelIO. For example:
```
   foo :: IO a -> IO a
   foo' :: MonadPeelIO m => m a -> m a
   foo' a = do
     k <- peelIO  -- k :: m a -> IO (m a)
     join $ liftIO $ foo (k a)  -- uses foo :: IO (m a) -> IO (m a)
```
Note that the "obvious" term of this type (peelIO = return return) does not work correctly. Instances of MonadPeelIO should be constructed via MonadTransPeel, using peelIO = liftPeel peelIO.

Instances11MonadPeelIO, …

MonadPeelIO IODefined in monad-peel-0.3 · Control.Monad.IO.Peel
MonadPeelIO m => MonadPeelIO (MaybeT m)Defined in monad-peel-0.3 · Control.Monad.IO.Peel
MonadPeelIO m => MonadPeelIO (ExceptT e m)Defined in monad-peel-0.3 · Control.Monad.IO.Peel
MonadPeelIO m => MonadPeelIO (IdentityT m)Defined in monad-peel-0.3 · Control.Monad.IO.Peel
MonadPeelIO m => MonadPeelIO (ReaderT r m)Defined in monad-peel-0.3 · Control.Monad.IO.Peel
MonadPeelIO m => MonadPeelIO (StateT s m)Defined in monad-peel-0.3 · Control.Monad.IO.Peel
MonadPeelIO m => MonadPeelIO (StateT s m)Defined in monad-peel-0.3 · Control.Monad.IO.Peel
(Monoid w, MonadPeelIO m) => MonadPeelIO (WriterT w m)Defined in monad-peel-0.3 · Control.Monad.IO.Peel
(Monoid w, MonadPeelIO m) => MonadPeelIO (WriterT w m)Defined in monad-peel-0.3 · Control.Monad.IO.Peel
(Monoid w, MonadPeelIO m) => MonadPeelIO (RWST r w s m)Defined in monad-peel-0.3 · Control.Monad.IO.Peel
(Monoid w, MonadPeelIO m) => MonadPeelIO (RWST r w s m)Defined in monad-peel-0.3 · Control.Monad.IO.Peel

valueliftIOOp

:: MonadPeelIO m
=> (a -> IO (m b)) -> IO (m c)
-> a -> m b
-> m c

#

liftIOOp is a particular application of peelIO that allows lifting control operations of type (a -> IO b) -> IO b (e.g. alloca, withMVar v) to MonadPeelIO m => (a -> m b) -> m b.

   liftIOOp f g = do
     k <- peelIO
     join $ liftIO $ f (k . g)

valueliftIOOp_ :: MonadPeelIO m => (IO (m a) -> IO (m b)) -> m a -> m b

#

liftIOOp_ is a particular application of peelIO that allows lifting control operations of type IO a -> IO a (e.g. block) to MonadPeelIO m => m a -> m a.

   liftIOOp_ f m = do
     k <- peelIO
     join $ liftIO $ f (k m)