type Agent<'T> = MailboxProcessor<'T>

/// Represents different messages 
/// handled by the stats agent
type StatsMessage = 
  | Add of float
  | Clear
  | GetAverage of AsyncReplyChannel<float>

let stats = 
  Agent.Start(fun inbox ->
    
    // Loops, keeping a list of numbers
    let rec loop nums = async {
      let! msg = inbox.Receive()
      match msg with 
      | Add num ->
          let newNums = num::nums
          return! loop newNums 
      | GetAverage repl ->
          repl.Reply(List.average nums)
          return! loop nums
      | Clear ->
          return! loop [] }    

    loop [] )

// Add error handler
stats.Error.Add(fun e -> printfn "Oops: %A" e)

// Post messages
stats.Post(Add(10.0))
stats.Post(Add(7.0))
stats.Post(Clear)
stats.PostAndReply(GetAverage)

(*

Chat room message:

 * NewMessage with name and text
 * GetAllMessages returns all messages 
   via AsyncReplyChannel

*)