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@agrafix
Last active Aug 29, 2015
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{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE RankNTypes #-}
module AtomicState
( getState, modifyState, forkThread, execAtomicStateT, AtomicStateT
, readState, runReadOnly, AtomicReadT
)
where
import Control.Monad.Reader
import Control.Concurrent
import Control.Concurrent.STM
newtype AtomicReadT r m a =
AtomicReadT { unpackAtomicReadT :: AtomicStateT r m a }
deriving (Monad, MonadIO, MonadTrans)
readState :: MonadIO m => AtomicReadT r m r
readState =
AtomicReadT $ getState
runReadOnly :: MonadIO m => AtomicReadT r m r -> AtomicStateT r m r
runReadOnly readOnlyAction =
unpackAtomicReadT readOnlyAction
newtype AtomicStateT s m a =
AtomicStateT { unpackAtomicStateT :: ReaderT (TVar s) m a }
deriving (Monad, MonadIO, MonadTrans)
getState :: MonadIO m => AtomicStateT s m s
getState =
AtomicStateT $
do var <- ask
liftIO $ atomically $ readTVar var
modifyState :: MonadIO m => (s -> s) -> AtomicStateT s m ()
modifyState f =
AtomicStateT $
do var <- ask
liftIO $ atomically $ modifyTVar var f
forkThread :: MonadIO m
=> AtomicStateT s m ()
-> (forall a. m a -> IO a)
-> AtomicStateT s m ThreadId
forkThread thread ioLift =
AtomicStateT $
do var <- ask
liftIO $ forkIO $ ioLift (runReaderT (unpackAtomicStateT thread) var)
execAtomicStateT :: MonadIO m => AtomicStateT s m a -> s -> m (s, a)
execAtomicStateT action initSt =
do var <- liftIO $ newTVarIO initSt
res <- runReaderT (unpackAtomicStateT action) var
st' <- liftIO $ atomically $ readTVar var
return (st', res)
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