if (numeric) {
	    if (((NumericValueExp)val1).isLong()) {
		lval1 = ((NumericValueExp)val1).longValue();
		lval2 = ((NumericValueExp)val2).longValue();

		switch (op) {
		case Query.PLUS:
		    return Query.value(lval1 + lval2);
		case Query.TIMES:
		    return Query.value(lval1 * lval2);
		case Query.MINUS:
		    return Query.value(lval1 - lval2);
		case Query.DIV:
		    return Query.value(lval1 / lval2);
		}
		
	    } else {
		dval1 = ((NumericValueExp)val1).doubleValue();
		dval2 = ((NumericValueExp)val2).doubleValue();

		switch (op) {
		case Query.PLUS:
		    return Query.value(dval1 + dval2);
		case Query.TIMES:
		    return Query.value(dval1 * dval2);
		case Query.MINUS:
		    return Query.value(dval1 - dval2);
		case Query.DIV:
		    return Query.value(dval1 / dval2);
		}
	    }
	} else {
	    sval1 = ((StringValueExp)val1).getValue();
	    sval2 = ((StringValueExp)val2).getValue();

	    switch (op) {
	    case Query.PLUS:
		return new StringValueExp(sval1 + sval2);
	    default:
		throw new BadStringOperationException(opString());
	    }
	}
	
	throw new BadBinaryOpValueExpException(this);
    } 

    /**
     * Returns the string representing the object
     */
    public String toString()  { 
	try {
	    return exp1 + " " + opString() + " " + exp2;
	} catch (BadBinaryOpValueExpException ex) {
	    return "invalid expression";
	}
    } 
    
    private String opString() throws BadBinaryOpValueExpException {
	switch (op) {
	case Query.PLUS:
	    return "+";
	case Query.TIMES:
	    return "*";
	case Query.MINUS:
	    return "-";
	case Query.DIV:
	    return "/";
	}
	
	throw new BadBinaryOpValueExpException(this);
    }

 }