Effects

One of the major differences between Akkling and core Akka.FSharp APIs is concept of Effects. Effect a special descriptor, which may be returned from actor loop, that will cause it to perform some specific action. Currently Akkling core library defines following set of effects:

• Unhandled will cause message received in current recursive iteration to be marked as unhandled. By default unhandled messages will be send to dead letters event stream.
• Stop will cause current actor to immediately stop. It will send Terminated message to all monitoring actors. All messages waiting in actor mailbox or stash will be lost.
• Ignore it's an equivalent of empty action.

Effects can be combined using @ operator. In such case they will be applied in order, they were defined.

Additionally effects can be heavily used by plugin libraries, such as Akkling.Persistence, which defines some additional effects:

• Persist, PersistAll - those effects take an event or sequence of events and orders them to be stored inside event journal.
• PersistAsync, PersistAllAsync work similar to their synchronous cousins, however they can optimize event persisting mechanism by additional batching at cost of periodical actor's state inconsistency.
• Defer will schedule another actor's loop hoop, once batch of asynchronously persisted messages will be stored.

Example:

let helloRef = spawn system "hello-actor" <| fun m ->
    let rec loop () = actor {
        let! msg = m.Receive ()
        match msg with
        | "stop" -> return Stop
        | "unhandle" -> return Unhandled
        | x -> 
            printfn "%s" x
            return! loop ()
    }
    loop ()