Description

The macro checks that the sequence is a Boost PP seq. It returns 1 if it is a seq, else if returns 0.

d = The next available BOOST_PP_WHILE iteration.
sequence = a possible Boost PP seq

returns = 1 if it a seq, else returns 0.

A single set of parentheses, with a single element, is parsed as a tuple and not a seq. To be parsed as a seq the input needs to be more than one consecutive sets of parentheses, each with a single element of data.