A fast right Kan extension based Monad Transformer that can be used to generate an efficient CPS representation from any combination of monads from the Monad Transformer Library.

To use, just wrap the type of your monad in Ran: i.e. Ran (StateT MyState ReaderT MyEnv IO) Bool and use liftRan :: RanFunctor m => m a -> Ran m a and and lowerRan :: RanFunctor m => Ran m a -> m a to extract your original monad.

This is really just a fancy way of saying that m a is isomorphic to forall o. (a -> f o) -> g o for some definition of f and g that is chosen by m. In practice f and g are built up out of newtypes.

Ran m a is often more efficient than the straightforward monad m because CPS transforming can yield additional optimization opportunities. There are a few caveats to be aware of however. If you inspect the result multiple times then 'Ran m a' may have to recompute its result for each usage. To prevent this, either, use 'Ran m a' once, as in most straight-line monadic code, or explicitly call lowerRan on it and perform your repeated tests against the unlifted monad.

Since Ran m is a data type that depends on type families, Ran cannot be made an instance of MonadTrans, use liftRanT or inRan in place of lift as needed.