/** Our internal representation of a BinExpr
 * in the Q0 language.
 * See http://www.radford.edu/itec380/2009fall-ibarland/Hw06/hw06.html
 * 
 * @author Ian Barland
 * @version 2014.Nov.04
 */
public class BinExpr extends Expr {

  Expr left, right;
  String op;

  BinExpr( Expr _left, String _op, Expr _right ) {
    this.left  = _left;
    this.op    = _op;
    this.right = _right;
    }
  
  public String toString( /* BinExpr this */) {
    return "("
         + this.left.toString()
         + " "
         + op
         +" "
         + this.right.toString()
         + ")";
      }
    
  public Value eval( /* BinExpr this */) {
    double leftValue  = ((Num)(this.left .eval())).doubleValue();
    double rightValue = ((Num)(this.right.eval())).doubleValue();
    if (this.op.equals("mul")) {
      return new Num(leftValue * rightValue);
      }
   else if (this.op.equals("add")) {
      return new Num(leftValue + rightValue);
      }
   else if (this.op.equals("sub")) {
      return new Num(leftValue - rightValue);
      }
   else {
      throw new RuntimeException("BinExpr.eval(): unknown binary operator `" + this.op + "`");
      }
    }
  
  @Override
  public boolean equals( /* BinExpr this, */ Object that) {
    if (this==that) {
      return true;
      }
   else if (that==null) {
      return false;
      }
   else if (this.getClass() != that.getClass()) {
      return false;
      }
   else {
      BinExpr thatt = (BinExpr) that;
      return this.left.equals(thatt.left)
          && this.op.equals(thatt.op)
          && this.right.equals(thatt.right);
      }
    
    }
    
  @Override
  public int hashCode() {
    if (cachedHash == null) {
      int hashSoFar = 0x814F8614; // fingerprint
      hashSoFar += this.left.hashCode();
      hashSoFar *= 31;
      hashSoFar += this.op.hashCode();
      hashSoFar *= 31;
      hashSoFar += this.right.hashCode();
      cachedHash = hashSoFar;
      }
    return cachedHash;
    }
  private Integer cachedHash = null;

  }