Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. — Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

Global _p

boost::parser::_p

// In header: <boost/parser/parser.hpp>

unspecified _p;

An invocable that returns the Ith parameter to the bottommost rule. This is useful for forwarding parameters to sub-rules.