Yield.hs

module Control.Monad.Schedule.Yield where

-- base
import qualified Control.Concurrent as Concurrent
import Control.Monad.IO.Class
import Data.Functor.Identity (Identity (runIdentity))

-- monad-schedule
import Control.Monad.Schedule.Class
import Control.Monad.Schedule.Trans

-- * 'YieldT'

-- | A monad for scheduling with cooperative concurrency.
type YieldT = ScheduleT ()

type Yield = YieldT Identity

-- | Let another thread wake up.
yield :: Monad m => YieldT m ()
yield = wait ()

runYieldT :: Monad m => YieldT m a -> m a
runYieldT = runScheduleT $ const $ return ()

runYield :: Yield a -> a
runYield = runIdentity . runYieldT

-- | Run a 'YieldT' value in a 'MonadIO',
--   interpreting 'yield's as GHC concurrency yields.
runYieldIO
  :: MonadIO m
  => YieldT m a -> m a
runYieldIO = runScheduleT $ const $ liftIO Concurrent.yield