Tony Morris (@dibblego) is no stranger to this site and in this talk he unlocks monad transformers. His examples are in Haskell but as always he explains the concepts for a general audience.

Monad transformers exist, mostly because monads don’t compose in the general case. Embracing them helps simplify your monadic code a great deal and is something you can use in your everyday programming.

You can find the talk here on Vimeo and the slides here.