BOOST_VMD_IS_PARENS_EMPTY_D — Determines if the sequence is a set of parens with no data. Re-entrant version.
// In header: <boost/vmd/is_parens_empty.hpp> BOOST_VMD_IS_PARENS_EMPTY_D(d, sequence)
d = The next available BOOST_PP_WHILE iteration. sequence = a VMD sequence
returns = 1 if the sequence is a set of parens with no data, else returns 0.
A set of parens with no data may be:
1) a tuple whose size is a single element which is empty or
2) a single element seq whose data is empty