<'
struct packet {
    length: int;
    keep length < 513;
    keep length > 63;
};

struct tx_gen {
   !packets: list of packet; 
   keep packets.size() == 2;
   !packet : packet;

   txgen () is {
     gen packets;
     out("--------Generated---------------------");
     print packets;
     for each (packet) in packets do {
       packet_class(packet); 
     };
     out("--------With it------------------------");
     for each  in packets do {
       packet_class(it); 
     };
     out("--------With reverse-------------------");
     for each  in reverse packets do {
       outf("Current packet position is %d\n", index );
       packet_class(it); 
     };

   };

   packet_class (pkt : packet) is {
     outf("Current size of packet : %d\n",pkt.length);
   }; 
}; 

extend sys {
  U_txgen : tx_gen;
  run() is also {
    U_txgen.txgen();
  };
};
'>