//Reads natural numbers, prepending them into a linked list. 
//Stops reading after a 0 is read.  At that point, the list is printed.

//The net effect is that a list of numbers gets printed in the
//reverse order from which they were read.

class LinkedList extends Object {
  nat data;  //content of a list node
  LinkedList next; //(implicit pointer to) the remainder of the list
  
  //set the data value in the list's head node to newData
  //returns newData
  nat setData(nat newData) { data=newData; }

  //prepend a new node to the list 
  //the new node will contain the newData 
  //always returns 0
  nat prepend(nat newData) {
    LinkedList currList;
    currList = new LinkedList();
    currList.data = data;
    currList.next = next;
    data = newData;
    next = currList;
    0;
  }

  //print the list
  //always returns 0
  nat printList(nat unused) {
    //print the data in this list node
    printNat(data);
    //if there's more to the list, recursively print the remainder 
    if(next==null) {0;}
    else {next.printList(0);};
  }
}

main {
  nat input;
  //create a linked list
  LinkedList ll;
  ll = new LinkedList();

  //read data into the list
  input = readNat();
  for(ll.setData(input); !(input==0); ll.prepend(input)) {
    input = readNat();
  };

  //print the list
  ll.printList(0);
}