A modular monad transformer library, (almost) a drop-in replacement for the monad transformer library (mtl). It provides a uniform lifting of operations through any monad transformer. Known differences with mtl: - It provides a uniform lifting of operations for any monad transformer. - It does not provide a RWS monad (but you can build it yourself ;) - The class MonadTrans requires a new member function tmap. - The lifting of callCC through StateT coincides with the lifting in MonadLib, but not with the lifting in mtl.