This module defines the CPS monad transformer.

#ContT Source

newtype ContT r m a

The CPS monad transformer.

This monad transformer extends the base monad with the operation callCC.


  • ContT ((a -> m r) -> m r)


#runContT Source

runContT :: forall a m r. ContT r m a -> (a -> m r) -> m r

Run a computation in the ContT monad, by providing a continuation.

#mapContT Source

mapContT :: forall a m r. (m r -> m r) -> ContT r m a -> ContT r m a

Modify the underlying action in a ContT monad action.

#withContT Source

withContT :: forall b a m r. ((b -> m r) -> (a -> m r)) -> ContT r m a -> ContT r m b

Modify the continuation in a ContT monad action

Re-exports from Control.Monad.Cont.Class

#MonadCont Source

class (Monad m) <= MonadCont m  where

The MonadCont type class represents those monads which support the callCC, or call-with-current-continuation operation.

This action makes the current continuation available to the caller.

For example:

delay :: forall eff. Number -> ContT Unit (Eff (timeout :: Timeout | eff)) Unit
delay n = callCC \cont ->
  lift $ setTimeout n (runContT (cont unit) (\_ -> return unit))

An implementation is provided for ContT, and for other monad transformers defined in this library.


  • callCC :: forall a. ((forall b. a -> m b) -> m a) -> m a

Re-exports from Control.Monad.Trans.Class

#MonadTrans Source

class MonadTrans t  where

The MonadTrans type class represents monad transformers.

A monad transformer is a type constructor of kind (* -> *) -> * -> *, which takes a Monad as its first argument, and returns another Monad.

This allows us to add additional effects to an existing monad. By iterating this process, we create monad transformer stacks, which contain all of the effects required for a particular computation.

The laws state that lift is a Monad morphism.


  • lift (pure a) = pure a
  • lift (do { x <- m ; y }) = do { x <- lift m ; lift y }