ref-mtl-0.3: Control/Monad/Ref.hs
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--------------------------------------------------------------------------------
-- |
-- Module : Control.Monad.Ref
-- Copyright : (c) Harvard University 2006-2011
-- License : BSD-style
-- Maintainer : mainland@eecs.harvard.edu
--
-- Stability : experimental
-- Portability : non-portable
--
--------------------------------------------------------------------------------
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE FunctionalDependencies #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE UndecidableInstances #-}
module Control.Monad.Ref (
MonadRef(..),
MonadAtomicRef(..)
) where
import Control.Concurrent.STM (STM)
import Control.Concurrent.STM.TVar (TVar,
newTVar,
readTVar,
writeTVar)
import Control.Monad.ST (ST)
import Control.Monad.Trans.Cont (ContT)
import Control.Monad.Trans.Error (ErrorT, Error)
import Control.Monad.Trans.Identity (IdentityT)
import Control.Monad.Trans.List (ListT)
import Control.Monad.Trans.Maybe (MaybeT)
import Control.Monad.Trans.Reader (ReaderT)
import Control.Monad.Trans.State.Lazy as Lazy (StateT)
import Control.Monad.Trans.State.Strict as Strict (StateT)
import Control.Monad.Trans.Writer.Lazy as Lazy (WriterT)
import Control.Monad.Trans.Writer.Strict as Strict (WriterT)
import Control.Monad.Trans.Class (lift)
import Data.IORef (IORef,
atomicModifyIORef,
modifyIORef,
newIORef,
readIORef,
writeIORef)
import Data.Monoid (Monoid)
import Data.STRef (STRef,
modifySTRef,
newSTRef,
readSTRef,
writeSTRef)
-- |The 'MonadRef' type class abstracts over the details of manipulating
-- references, allowing one to write code that uses references and can operate
-- in any monad that supports reference operations.
class (Monad m) => MonadRef r m | m -> r where
-- |Create a new reference
newRef :: a -> m (r a)
-- |Read the value of a reference
readRef :: r a -> m a
-- |Write a new value to a reference
writeRef :: r a -> a -> m ()
-- |Mutate the contents of a reference
modifyRef :: r a -> (a -> a) -> m ()
modifyRef r f = readRef r >>= writeRef r . f
class (MonadRef r m) => MonadAtomicRef r m | m -> r where
-- |Atomically mutate the contents of a reference
atomicModifyRef :: r a -> (a -> (a, b)) -> m b
instance MonadRef (STRef s) (ST s) where
newRef = newSTRef
readRef = readSTRef
writeRef = writeSTRef
modifyRef = modifySTRef
instance MonadRef IORef IO where
newRef = newIORef
readRef = readIORef
writeRef = writeIORef
modifyRef = modifyIORef
instance MonadRef TVar STM where
newRef = newTVar
readRef = readTVar
writeRef = writeTVar
instance MonadRef r m => MonadRef r (ContT r' m) where
newRef r = lift $ newRef r
readRef r = lift $ readRef r
writeRef r x = lift $ writeRef r x
modifyRef r f = lift $ modifyRef r f
instance (Error e, MonadRef r m) => MonadRef r (ErrorT e m) where
newRef r = lift $ newRef r
readRef r = lift $ readRef r
writeRef r x = lift $ writeRef r x
modifyRef r f = lift $ modifyRef r f
instance MonadRef r m => MonadRef r (IdentityT m) where
newRef r = lift $ newRef r
readRef r = lift $ readRef r
writeRef r x = lift $ writeRef r x
modifyRef r f = lift $ modifyRef r f
instance MonadRef r m => MonadRef r (ListT m) where
newRef r = lift $ newRef r
readRef r = lift $ readRef r
writeRef r x = lift $ writeRef r x
modifyRef r f = lift $ modifyRef r f
instance MonadRef r m => MonadRef r (MaybeT m) where
newRef r = lift $ newRef r
readRef r = lift $ readRef r
writeRef r x = lift $ writeRef r x
modifyRef r f = lift $ modifyRef r f
instance MonadRef r m => MonadRef r (ReaderT r' m) where
newRef r = lift $ newRef r
readRef r = lift $ readRef r
writeRef r x = lift $ writeRef r x
modifyRef r f = lift $ modifyRef r f
instance MonadRef r m => MonadRef r (Lazy.StateT s m) where
newRef r = lift $ newRef r
readRef r = lift $ readRef r
writeRef r x = lift $ writeRef r x
modifyRef r f = lift $ modifyRef r f
instance MonadRef r m => MonadRef r (Strict.StateT s m) where
newRef r = lift $ newRef r
readRef r = lift $ readRef r
writeRef r x = lift $ writeRef r x
modifyRef r f = lift $ modifyRef r f
instance (Monoid w, MonadRef r m) => MonadRef r (Lazy.WriterT w m) where
newRef r = lift $ newRef r
readRef r = lift $ readRef r
writeRef r x = lift $ writeRef r x
modifyRef r f = lift $ modifyRef r f
instance (Monoid w, MonadRef r m) => MonadRef r (Strict.WriterT w m) where
newRef r = lift $ newRef r
readRef r = lift $ readRef r
writeRef r x = lift $ writeRef r x
modifyRef r f = lift $ modifyRef r f
instance MonadAtomicRef IORef IO where
atomicModifyRef = atomicModifyIORef
instance MonadAtomicRef TVar STM where
atomicModifyRef r f = do x <- readRef r
let (x', y) = f x
writeRef r x'
return y
instance MonadAtomicRef r m => MonadAtomicRef r (ContT r' m) where
atomicModifyRef r f = lift $ atomicModifyRef r f
instance (Error e, MonadAtomicRef r m) => MonadAtomicRef r (ErrorT e m) where
atomicModifyRef r f = lift $ atomicModifyRef r f
instance MonadAtomicRef r m => MonadAtomicRef r (IdentityT m) where
atomicModifyRef r f = lift $ atomicModifyRef r f
instance MonadAtomicRef r m => MonadAtomicRef r (ListT m) where
atomicModifyRef r f = lift $ atomicModifyRef r f
instance MonadAtomicRef r m => MonadAtomicRef r (MaybeT m) where
atomicModifyRef r f = lift $ atomicModifyRef r f
instance MonadAtomicRef r m => MonadAtomicRef r (ReaderT r' m) where
atomicModifyRef r f = lift $ atomicModifyRef r f
instance MonadAtomicRef r m => MonadAtomicRef r (Lazy.StateT s m) where
atomicModifyRef r f = lift $ atomicModifyRef r f
instance MonadAtomicRef r m => MonadAtomicRef r (Strict.StateT s m) where
atomicModifyRef r f = lift $ atomicModifyRef r f
instance (Monoid w, MonadAtomicRef r m) => MonadAtomicRef r (Lazy.WriterT w m) where
atomicModifyRef r f = lift $ atomicModifyRef r f
instance (Monoid w, MonadAtomicRef r m) => MonadAtomicRef r (Strict.WriterT w m) where
atomicModifyRef r f = lift $ atomicModifyRef r f