try {
if (getOperator(this.getEntity()) == SUMA) {
ret = ret.suma(((Expression) expr[1]).evaluateExpression(
row));
} else if (getOperator(this.getEntity()) == RESTA) {
ret = ret.suma(ValueFactory.createValue(-1).producto(((Expression) expr[1]).evaluateExpression(
row)));
}
} catch (IncompatibleTypesException e) {
throw new EvaluationException(e);
}