/** Our internal representation of a BinExpr
 * in the O0 language.
 * See http://www.radford.edu/itec380/2009fall-ibarland/Hw06/hw06.html
 * 
 * @author Ian Barland
 * @version 2008.Nov.30
 */
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() {
    return "("
         + this.left.toString()
         + " "
         + this.op
         + " "
         + this.right.toString()
         + ")"
         ;
    }
    
  public Value eval() {
    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 operator `" + this.op + "`");
      }
    }
    
  }