public override object Exec(ClassType caller, object arg)
        {
            //TODO: comprobar si es el name de caller.
            MethodType method = (MethodType)caller.AcceptOperation(DotOperation.Create(caller.Name, new List <TypeExpression>()), arg);

            if (method == null)
            {
                return(null);
            }
            return(method.AcceptOperation(this, arg));
        }