Boost C++ Libraries

Description

The lazy parser, as its name suggests, invokes a lazy Phoenix function that returns a parser at parse time. This parser will be used once it is created to continue the parse.

Header

// forwards to <boost/spirit/home/qi/auxiliary/lazy.hpp>
#include <boost/spirit/include/qi_lazy.hpp>

Also, see Include Structure.

Namespace

Model of

Expression Semantics

Semantics of an expression is defined only where it differs from, or is not defined in Parser.

Attributes

Complexity

The complexity of the lazy parser is determined by the complexity of the parser returned from fp.

Example

	Note
	The test harness for the example(s) below is presented in the Basics Examples section.

Some using declarations:

using boost::spirit::qi::lazy;
using boost::spirit::ascii::string;
using boost::phoenix::val;

Using lazy:

Here, the phoenix::val expression creates a function that returns its argument when invoked. The lazy expression defers the invocation of this function at parse time. Then, this parser (string parser) is called into action. All this takes place at parse time.

test_parser("Hello", lazy(val(string("Hello"))));

The above is equivalent to:

test_parser("Hello", val(string("Hello")));