Phoenix

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

l[phoenix-lambda-expression]

Spirit.Lex provides some Boost.Phoenix placeholders to access important information from the Context that are otherwise difficult to extract.

Spirit.Lex specific Phoenix placeholders

_start, _end: Iterators pointing to the begin and the end of the matched input sequence.
_pass: Assign lex::pass_flags::pass_fail to _pass to force the current match to fail.
_tokenid: The token id of the matched token.
_val: The token value of the matched token.
_state: The lexer state the token has been matched in.
_eoi: Iterator referring to the current end of the input sequence.

	Tip
	All of the placeholders in the list above (except `_eoi`) can be changed from the inside of the semantic action allowing to modify the lexer behavior. They are defined in the namespace `boost::spirit::lex`.

For more information see Lexer Semantic Actions.