boost::qi evaluate result by last sequential item

I have rather complicated expression parser with strict type checking. So my expression rule declared to return effective type-index. Like that:

qi::rule < Iterator, type_index_t, skipper<Iterator>> 
    set_expression, expression, single_expression;

Now I have chaining multiple expression by rule:

expression = ((single_expression|set_expression) >> -(expression) )[
                // following looks redundant
                qi::_val = boost::phoenix::if_else(qi::_2, *qi::_2, qi::_1)
            ]
            | qi::lit('(') >> expression >> ')'
            ;

Without explicit semantic action with if_else I got wrong result of type of first entry instead of the last one.

So my question: is there better way to obtain correct expression type that equals to last item in sequence?