package tarau.jinni;
import java.util.Stack;

/**
 * Varable-like entity, with a multiple values, in stack order.
 * Set operations are undone on backtraking, when the previous
 * value is restored.
 */
class MultiVar extends Fluent  {
  Stack vals;

  MultiVar(Term T,Prog p)  {
     super(p);
     vals=new Stack();
     vals.push(T.ref());
  }

  final void set(Term T,Prog p) {
    vals.push(T);
    p.getTrail().push(this);
  }
  
  public Term val() {
      return (Term)vals.peek();
  }
  
  /** 
   * cannot be made presistent
  */
  protected void undo() {
     vals.pop();
  }
  
  public String toString() {
    return "MultiVar["+vals.size()+"]->{"+vals.peek().toString()+"}";
  }
}