Phoenix

Boost.Phoenix makes it easier to attach semantic actions. You just inline your lambda expressions:

p[phoenix-lambda-expression]

Spirit.Qi provides some Boost.Phoenix placeholders to important information from the Attrib and Context that are otherwise fiddly to extract.

Spirit.Qi specific Phoenix placeholders

_1, _2... , _N: Nth attribute of p
_val: The enclosing rule's synthesized attribute.
_r1, _r2... , _rN: The enclosing rule's Nth inherited attribute.
_a, _b... , _j: The enclosing rule's local variables (_a refers to the first).
_pass: Assign false to _pass to force a parser failure.

	Important
	All placeholders mentioned above are defined in the namespace `boost::spirit` and, for your convenience, are available in the namespace `boost::spirit::qi` as well.

For more detailed information about semantic actions see: here.

Boost C++ Libraries