Hello, it’s already problematic, that State, StateT etc. are under Control.Monad. While they are monads, they are also applicative functors, for example. And some “monad transformers” are also applicative functor transformers and probably all of them are functor transformers. There are situations where you want to use these types only as applicative functors, for example when composing context-free parsers. Since they are all functors at least, it might be sensible to put them under Control.Functor. Or it might be a good idea to put them under Data in the module hierarchy. That way, a compatibility package could provide the old interface under Control.Monad and new stuff would be situated under Control.Functor or Data. During this restructuring, we could also rename State to StateTrans since values of State are not states but state transformers. There are similar problems with Cont since values of Cont type are not continuations but functions from continuations to results. It’s problematic when you deal with states and state transformers or continuations and Cont values. How do you name your local variables? I’d like to say “state” for a state but it would also be sensible to say “state” for a value of type State, i.e., a state transformer. Comments? Ideas? Best wishes, Wolfgang