Control.Monad.Class.MonadST

Documentation

class Monad m => MonadST m where

This class is for abstracting over stToIO which allows running ST actions in IO. In this case it is to allow running ST actions within another monad m.

The type of stToIO is:

stToIO : ST RealWorld a -> IO a

Abstracting over this is tricky because we need to not care about both the IO, and also the RealWorld.

A solution is to write an action that is given the liftST as an argument and where that action itself is polymorphic in the s parameter. This allows us to instantiate it with RealWorld in the IO case, and the local s in a case where we are embedding into another ST action.

Methods

withLiftST :: (forall s. (forall a. ST s a -> m a) -> b) -> b

Instances

MonadST IO

Defined in Control.Monad.Class.MonadST

Methods

withLiftST :: (forall s. (forall a. ST s a -> IO a) -> b) -> b

MonadST (ST s)

Defined in Control.Monad.Class.MonadST

Methods

withLiftST :: (forall s0. (forall a. ST s0 a -> ST s a) -> b) -> b

MonadST m => MonadST (ReaderT r m)

Defined in Control.Monad.Class.MonadST

Methods

withLiftST :: (forall s. (forall a. ST s a -> ReaderT r m a) -> b) -> b