Types Following Colons In Channel Definitions?

Question

The Axum Programmer's Guide contains this application:

using System;
using Microsoft.Axum;
using System.Concurrency.Messaging;

namespace Project06
{
  schema Pair
	{
    required int Num1;
    required int Num2;
	}
  
  channel Adder
	{
    input Pair Nums : int;
  }
  
	agent AdderAgent : channel Adder
	{
		public AdderAgent()
		{
      while(true)
      {
        var result = receive(PrimaryChannel::Nums);
        result <-- result.RequestValue.Num1 + result.RequestValue.Num2;
      }
		}
	}

  agent MainAgent : channel Microsoft.Axum.Application
  {
    public MainAgent()
    {
      var adder = AdderAgent.CreateInNewDomain();
      var correlator1 = adder::Nums <-- new Pair { Num1=10, Num2=20 };
      var correlator2 = adder::Nums <-- new Pair { Num1=30, Num2=40 };
      var sum1 = receive(correlator1);
      Console.WriteLine(sum1);
      var sum2 = receive(correlator2);
      Console.WriteLine(sum2);
      PrimaryChannel::ExitCode <-- 0;
    }
  }
}

What is the function of the "int" keyword to the right of the colon in the channel definition?

Answer 1

Hi Jeff,

 

You'll find more about this in the language spec. (p7-8). Basically - and this is paraphrased from the spec. - it binds, more closely, a "reply value" to the port. Notice that in your code you're both sending, using the "<--" operator and receiving, using receive(), on the port Nums. You're only able to do this because we're explicitly saying that Nums has a reply value of type int.

I am not 100% at which point the relationship is created between the lines:

 

var result = receive(PrimaryChannel::Nums);
result <-- result.RequestValue.Num1 + result.RequestValue.Num2;

and the port, however. Maybe some one who actually knows can pick this up ;)

 

P.S. Jeff, did you get my e-mail?

 

Answer 2

Thank you, Antony. I'll take a closer look at my code.

 

PS. I don't see an email from you, but I welcome it ... send it to JEFFREY DOT FERGUSON AT GMAIL DOT COM for fastest results (note that its jeffREY and not jeffERY).

Answer 3

Anthony's answer is correct -- this is the request-reply port. The receive method returns a correlator, which is a generic type. (This is why you really want to use 'var' here and not write the type explicitly -- it is rather unwieldy)

---

Artur Laksberg - MSFT