PrinterExample.fsx

[<AutoOpen>]
module Output =

    type internal OutputMessage = 
        | Print of string

    type Printer(output : (string -> unit)) =
        let agent = MailboxProcessor<OutputMessage>.Start(fun inbox ->
            let rec loop () = async {
                let! message = inbox.Receive() 
                match message with
                | Print msg -> 
                    output msg;
                    return! loop() }
            loop() )

        member _.Print text = agent.Post(Print text)

//test
let consolePrinter = Printer(System.Console.Out.WriteLine)
consolePrinter.Print("Hello!")
consolePrinter.Print("Goodbye!")

// fsi:
// Hello!
// val it : unit = ()
// Goodbye!
// val it : unit = ()