package ppmrmn;

public class ListGentle  {

  private Node start, now, prev;

  public ListGentle () {
    now   = null;
    start = null;
    prev  = null;
  }

  public void add(Object x) {
    prev = now;
    if (start == null) {
      start = new Node (x, null);
      now = start;
    }
    else {
      Node T = new Node (x, now.link);
      now.link = T;
      now = T;
    }
  }

  public void remove() {
    if (isempty() || eol()) {
      return;
    }
    else {
      if (prev == null) {
        start = now.link;
      }
      else {
        prev.link = now.link;
        now = now.link;
      }
    }
  }

  public boolean isempty() {
    return start == null;
  }

  public Object current() {
    return now.data;
  }

  public void reset() {
    now = start;
    prev = null;
  }

  public boolean eol() {
    return now.link == null;
  }

  public void succ() {
    now = now.link;
    if (prev == null)
      prev = start;
    else
      prev = prev.link;
  }
}

class Node {
  Node link;
  Object data;
  /* The constructor copies in the data and the link to the given node
   * (which may be null).
   */

  Node(Object d, Node n) {
    link = n;
    data = d;
  }
}