Thanks! Definitely, actors and fibers can co-exist. However, fibers are the lower-level primitive on top of which actors can be implemented, not a replacement for actors as a concurrency tool, which was what I was trying to argue int he article.

Replacting `IO` with "monad" would be too general, as there are many monads which do not describe side-effectful computations, and have vastly different use-cases than `Future`s or fibers.