A function that runs a transformed monad t n on the monadic state that was captured by liftWith

A Run t function yields a computation in n that returns the monadic state of t. This state can later be used to restore a t computation using restoreT.

Example type equalities:

Run IdentityT    ~ forall n b. Monad n             => IdentityT  n b -> n b
Run MaybeT       ~ forall n b. Monad n             => MaybeT     n b -> n (Maybe b)
Run (ErrorT e)   ~ forall n b. (Monad n, Error e)  => ErrorT e   n b -> n (Either e b)
Run (ExceptT e)  ~ forall n b. Monad n             => ExceptT e  n b -> n (Either e b)
Run ListT        ~ forall n b. Monad n             => ListT      n b -> n [b]
Run (ReaderT r)  ~ forall n b. Monad n             => ReaderT r  n b -> n b
Run (StateT s)   ~ forall n b. Monad n             => StateT s   n b -> n (a, s)
Run (WriterT w)  ~ forall n b. (Monad n, Monoid w) => WriterT w  n b -> n (a, w)
Run (RWST r w s) ~ forall n b. (Monad n, Monoid w) => RWST r w s n b -> n (a, s, w)

A function like Run that runs a monad transformer t which wraps the monad transformer t'. This is used in defaultLiftWith.

Default definition for the liftWith method.

Default definition for the restoreT method.

A function like Run that runs a monad transformer t which wraps the monad transformers n and n'. This is used in defaultLiftWith2.

Default definition for the liftWith method.

Default definition for the restoreT method for double MonadTransControl.

A function that runs a m computation on the monadic state that was captured by liftBaseWith

A RunInBase m function yields a computation in the base monad of m that returns the monadic state of m. This state can later be used to restore the m computation using restoreM.

Example type equalities:

RunInBase (IdentityT  m) b ~ forall a.             IdentityT  m a -> b (StM m a)
RunInBase (MaybeT     m) b ~ forall a.             MaybeT     m a -> b (StM m (Maybe a))
RunInBase (ErrorT e   m) b ~ forall a. Error e =>  ErrorT e   m a -> b (StM m (Either e a))
RunInBase (ExceptT e  m) b ~ forall a.             ExceptT e  m a -> b (StM m (Either e a))
RunInBase (ListT      m) b ~ forall a.             ListT      m a -> b (StM m [a])
RunInBase (ReaderT r  m) b ~ forall a.             ReaderT    m a -> b (StM m a)
RunInBase (StateT s   m) b ~ forall a.             StateT s   m a -> b (StM m (a, s))
RunInBase (WriterT w  m) b ~ forall a. Monoid w => WriterT w  m a -> b (StM m (a, w))
RunInBase (RWST r w s m) b ~ forall a. Monoid w => RWST r w s m a -> b (StM m (a, s, w))

Handy type synonym that composes the monadic states of t and m.

It can be used to define the StM for new MonadBaseControl instances.

A function like RunInBase that runs a monad transformer t in its base monad b. It is used in defaultLiftBaseWith.

Default defintion for the liftBaseWith method.

Note that it composes a liftWith of t with a liftBaseWith of m to give a liftBaseWith of t m:

defaultLiftBaseWith = \f -> liftWith $ \run ->
                              liftBaseWith $ \runInBase ->
                                f $ runInBase . run

Default definition for the restoreM method.

Note that: defaultRestoreM = restoreT . restoreM

An often used composition: control f = liftBaseWith f >>= restoreM

Embed a transformer function as an function in the base monad returning a mutated transformer state.

Performs the same function as embed, but discards transformer state from the embedded function.

Capture the current state of a transformer

Capture the current state above the base monad

liftBaseOp is a particular application of liftBaseWith that allows lifting control operations of type:

((a -> b c) -> b c) to: (MonadBaseControl b m => (a -> m c) -> m c).

For example:

liftBaseOp alloca :: MonadBaseControl IO m => (Ptr a -> m c) -> m c

liftBaseOp_ is a particular application of liftBaseWith that allows lifting control operations of type:

(b a -> b a) to: (MonadBaseControl b m => m a -> m a).

For example:

liftBaseOp_ mask_ :: MonadBaseControl IO m => m a -> m a

liftBaseDiscard is a particular application of liftBaseWith that allows lifting control operations of type:

(b () -> b a) to: (MonadBaseControl b m => m () -> m a).

Note that, while the argument computation m () has access to the captured state, all its side-effects in m are discarded. It is run only for its side-effects in the base monad b.

For example:

liftBaseDiscard forkIO :: MonadBaseControl IO m => m () -> m ThreadId

liftBaseOpDiscard is a particular application of liftBaseWith that allows lifting control operations of type:

((a -> b ()) -> b c) to: (MonadBaseControl b m => (a -> m ()) -> m c).

Note that, while the argument computation m () has access to the captured state, all its side-effects in m are discarded. It is run only for its side-effects in the base monad b.

For example:

liftBaseDiscard (runServer addr port) :: MonadBaseControl IO m => m () -> m ()

Transform an action in t m using a transformer that operates on the underlying monad m