Multiple things at once are still ordinary monads, and you can implement them without using transformers. Transformers are merely the realization that one can p

Multiple things at once are still ordinary monads, and you can implement them without using transformers. Transformers are merely the realization that one can put (certain) monads together in a compositional way. An example of a monad in Haskell that is not put together via transformers, yet provides all their functionality, is RWS, being a combination of Reader, Writer and State in one hard-coded type/instance.