Selective Receive with F# MailboxProcessor

SelectiveReceive.fs

#light

open Microsoft.FSharp.Control

let counter =
    MailboxProcessor.Start(fun inbox ->
        let rec loop() =
            async {            
                let! msg = inbox.Scan(fun x -> 
                    match x with
                    | 1 -> Some(async { return x })
                    | _ -> None)
                do printf "%d " msg
                
                let! msg = inbox.Scan(fun x -> 
                    match x with
                    | 2 -> Some(async { return x })
                    | _ -> None)
                do printf "%d " msg
                
                return! loop() }
        loop());

for t = 1 to 5 do counter.Post(1)
for t = 1 to 5 do counter.Post(2)

Console.ReadLine() |> ignore

// output: 
// 1 2 1 2 1 2 1 2 1 2