/** Our internal representation of a Is0Expr
 * in the P0 language.
 * See http://www.radford.edu/itec380/2009fall-ibarland/Hw06/hw06.html
 * 
 * @author Ian Barland
 * @version 2014.Nov.04
 */
public class WhenZExpr extends Expr {
  static final String TOKEN = "whenz";
  
  Expr cond, thenPart, elsePart;
  
  WhenZExpr( Expr _cond, Expr _thenPart, Expr _elsePart) {
    this.cond = _cond;
    this.thenPart = _thenPart;
    this.elsePart = _elsePart;
    }
  
  public String toString() {
    return TOKEN
         + " "
         + cond.toString()
         + " then "
         + thenPart.toString()
         + " otherwise "
         + elsePart.toString()
         + "!";
    }
    
    
  public Value eval() {
    if (((Num)(cond.eval())).doubleValue() == 0) {
      return thenPart.eval();
      }
    else {
      return elsePart.eval();
      }
    }
    
  @Override
  public boolean equals( /* WhenZExpr this, */ Object that) {
    if (this==that) {
      return true;
      }
    else if (that==null) {
      return false;
      }
    else if (this.getClass() != that.getClass()) {
      return false;
      }
    else {
      WhenZExpr thatt = (WhenZExpr) that;
      return this.cond.equals(thatt.cond)
          && this.thenPart.equals(thatt.thenPart)
          && this.elsePart.equals(thatt.elsePart);
      }
    
    }
    
  @Override
  public int hashCode() {
    if (cachedHash == null) {
      int hashSoFar = (int) 3141949305892159L; // fingerprint
      hashSoFar += this.cond.hashCode();
      hashSoFar *= 31;
      hashSoFar += this.thenPart.hashCode();
      hashSoFar *= 31;
      hashSoFar += this.elsePart.hashCode();
      cachedHash = hashSoFar;
      }
    return cachedHash;
    }
  private Integer cachedHash = null; 
  }