Control.ContStuff.Trans

Monad transformers

Identity transformer

data IdentityT m a

ContT

data ContT r m a

Choice/nondeterminism

data ChoiceT r i m a

Exceptions

data EitherT r e m a

data MaybeT r m a

State

data StateT r s m a

Writer monads

type OldWriterT r w m a