use IPC::MPS;
 
 my $ping_pong = 3;
 
 my ($vpid1, $vpid2);
 
 $vpid1 = spawn {
        snd($vpid2, "ping", 1);
        receive { 
                msg pong => sub {
                        my ($from, $i) = @_;
                        print "Pong $i from $from\n";
                        if ($i < $ping_pong) {
                                snd($from, "ping", $i + 1);
                        } else {
                                snd(0, "exit");
                        }
                };
        };
 };
 
 $vpid2 = spawn { 
        receive {
                msg ping => sub {
                        my ($from, $i) = @_;
                        print "Ping ", $i, " from $from\n";
                        snd($from, "pong", $i);
                };
        };
 };
 
 receive {
        msg exit => sub {
                print "EXIT\n";
                exit;
        };
 };