I've been trying to find anything that discusses when you should favor the use of monads over actors (in concurrency scenarios), but I've found nothing. In particular, I'm wondering about the use of the Reactive Extensions (LINQ to Events) vs. F#'s MailboxProcessor. Please give examples in addition to any philosophical reasoning you might have.
Update For better context, the Reactive Extensions implement the continuation monad in the form of IObservable/IObserver. I'm not necessarily saying I have to use F#, just that F# has a concrete "actor model" available in a .NET language in the form of MailboxProcessor<'T>.
What I'm trying to understand is when to use a monad (in this case a continuation monad) vs. an actor model for concurrency purposes. Where the monad (as I understand it) doesn't introduce state, the actor has its own internal state that is modified as necessary to provide protected access.
I've seen a number of examples of using both: Rx and node.js (CPS, not really the continuation monad) vs. F#'s MailboxProcessor and Scala's Akka framework. I just don't know why you would choose one over the other.
I'm going to respond to my own question and say you should use both. This is based on Don Syme's post. A MbP uses the Async computation to do its work, and the Async is a thread-aware continuation monad. Looks like you can use it by itself for some uses, but the MbP definitely requires it.
I don't really like this answer, and I'd be happy for someone to respond with a better explanation of when to use each.
Updated:
See MiniRx, which is now apart of FSharpx, for an implementation of an Rx-style monad implemented using MailboxProcessor. As MailboxProcessor is itself implemented using the async monad, these pieced to indeed work together. They are just different means of abstraction.