Shows how to use visitors to transport objects.

Is simpler to express when propagation patterns are added
to Demeter/Java.

//class dictionary

// simplified cd for Triples transportation pattern example
// pages 320-325 in AP book.
Company = <customers> List(Customer).
Customer = "customer"
  <orders> List(Item)
  <name> String
  <location> String.
Item = "item"
  <made_by> Producer
  <name> String.
Producer = "producer"
  <name> String
  <location> String.
List(S) ~  {S} .

CustomerTV = 
  <name> String
  <location> String.
ProducerTV = 
  <name> String
  <location> String.
SameLocationV =
  <ctv> CustomerTV
  <ptv> ProducerTV.

Main = .
//behavior

// solves triples problem (simplified) from page 322 of my book
Company {
  traversal allProducers(
    SameLocationV slv,
    CustomerTV ctv,
    ProducerTV ptv
    ){
    to Producer;}

// allProducers
// Host/Visitor interaction
//		slv		ctv		ptv
//          -----------------------------------------
//  before			?,!ctv
//Customer		
//Item	 			
//  after	?ctv,?ptv
//  before					?,!ptv
//Producer	
//          -----------------------------------------
//Legend:
//  ?		read from host
//  ?ctv	read from visitor ctv
//  !		write to host
//  !ctv	write to visitor ctv

  (@
  // finds items for which customer and producer live
  // in the same location
  void same_location() {
    CustomerTV ctv = new CustomerTV();
    ProducerTV ptv = new ProducerTV();
    SameLocationV slv = new SameLocationV(ctv,ptv);
    this.allProducers(slv, ctv, ptv);
  } @) }
// customer transportation visitor
CustomerTV {
  before Customer (@
    name = host.get_name();
    location = host.get_location();
  @) }
// producer transportation visitor
ProducerTV {
  before Producer (@
    name = host.get_name();
    location = host.get_location();
  @) }
SameLocationV {
  after Item (@
    if (ctv.get_location().equals(ptv.get_location())) {
      System.out.println(
	" ctv= " +  ctv.get_name() + 
	" ptv= " +  ptv.get_name() + 
	" current item= " + host.get_name()); 
    }
  @) }


Main {
(@
  static public void main(String args[]) throws Exception {

    Runtime rt = Runtime.getRuntime();
    rt.traceMethodCalls(true);

    Company a = Company.parse(System.in);

    a.same_location();

    System.out.println("done ");
  }
@)
}
// input

customer
  item
     producer
     "Novartis"
     "Basel"
   "xyz1"
  "Huber"
  "Basel"
customer
  item
     producer
     "Novartis"
     "Basel"
   "xyz2"
  "Huber"
  "Geneva"
customer
  item
    producer
      "Novartis"
      "Basel"
  "xyz3"
  item
    producer
      "NovartisB"
      "Basel"
  "xyz4"
"HuberB"
"Basel"



// output from program


 ctv= Huber ptv= Novartis current item= xyz1
 ctv= HuberB ptv= Novartis current item= xyz3
 ctv= HuberB ptv= NovartisB current item= xyz4
done