/** class IfZero, our internal representation of a ifZero-expression
 * in the L0 language.
 * See http://www.radford.edu/itec380/2008fall/Hw06/hw06.html
 * 
 * @author Ian Barland
 * @version 2008.Nov.30
 */
public class IfZero extends Expr {
  static final String TOKEN = "ifZero";
  
  Expr cond, thenPart, elsePart;
  
  IfZero( Expr _cond, Expr _thenPart, Expr _elsePart) {
    this.cond = _cond;
    this.thenPart = _thenPart;
    this.elsePart = _elsePart;
    }
  
  public String toString() {
    return "{" + TOKEN 
         + " " + cond.toString()
         + " " + thenPart.toString()
         + " " + elsePart.toString()
         + "}";
    }
    
    
  public Value eval() {
    if (((Num)(cond.eval())).doubleValue() == 0) {
      return thenPart.eval();
      }
    else {
      return elsePart.eval();
      }
    }
  }