| Safe Haskell | Safe-Infered |
|---|
Control.Monad.Task
Description
Task monad transformer can help refactor event and callback heavy programs into monads via co-routines. The idea is loosely based on Combining Events And Threads For Scalable Network Services, by Peng Li and Steve Zdancewic, in PLDI, 2007. (http://www.cis.upenn.edu/~stevez/papers/abstracts.html#LZ07), but with deterministic and co-oprative lightweight threads, also known as co-routines, so that the base monad can be anything ranging from IO to state monads, or your favorite monad transformer stack.
Besides, Task monad transformer also provides a simple mechanism to signal and watch for events, which allows complex event processing logic to be expressed as streamlined monadic co-routines.
Task monad transformer is essentially a ContT, or continuation transformer, defined to extract the control flow of monadic programs with co-operative multi-threading. After the CPS transformation, the program trace is then executed with a simple round-robin scheduler.
MonadTask class
class Monad m => MonadTask e m | m -> e whereSource
MonadTask specifies a task monad m over an event type e.
Methods
yield temporarily suspends current task to let others run.
fork spawns a task and runs it immediate until it ends or
suspends before returning to current task.
watch :: (e -> Maybe a) -> m aSource
watch suspends current task to wait for future events, and will
resume execution when an event triggers its watching function.
signal broadcasts an event to all other tasks that are watching,
and give those who wake up the priority to run.
exit ends all tasks and return immediately.
Instances
| (Monad m, MonadTask a m) => MonadTask a (MaybeT m) | |
| (Monad m, MonadTask a m) => MonadTask a (ListT m) | |
| (Monad m, MonadTask a m) => MonadTask a (IdentityT m) | |
| (Monoid w, Monad m, MonadTask a m) => MonadTask a (WriterT w m) | |
| (Monoid w, Monad m, MonadTask a m) => MonadTask a (WriterT w m) | |
| (Monad m, MonadTask a m) => MonadTask a (ReaderT r m) | |
| (Error e, Monad m, MonadTask a m) => MonadTask a (ErrorT e m) | |
| Monad m => MonadTask e (TaskT e m) |
TaskT monad transformer
Task monad transformer.
Instances
| MonadReader s m => MonadReader s (TaskT e m) | |
| MonadState s m => MonadState s (TaskT e m) | |
| Monad m => MonadTask e (TaskT e m) | |
| MonadTrans (TaskT e) | |
| Monad m => Monad (TaskT e m) | |
| Functor (TaskT e m) | |
| Applicative (TaskT e m) | |
| MonadIO m => MonadIO (TaskT e m) |