A monad isn't a concrete thing, a monad is a pattern that lots of different types adhere to. So it makes sense to extract it into an interface, in that operatio

A monad isn't a concrete thing, a monad is a pattern that lots of different types adhere to. So it makes sense to extract it into an interface, in that operations that only use the monadicness can be implemented once for all types that are monads. It doesn't make much sense to study monads apart from the things that implement the interface, because there is not much to it. It's just an interface for the abstract notion of an ordered sequence of actions.