Can't use a rule parameter to pass a symbol table to a rule?

[jwwalker]

I tried the following, and the compiler wasn't happy about it. I guess the tutorial's discussion of parameters was too complicated for me.

#include <boost/parser/parser.hpp>

namespace bp = ::boost::parser;

bp::rule< struct toprule, double > toprule = "toprule";
auto const toprule_def = bp::double_ >> bp::_p<0>;
BOOST_PARSER_DEFINE_RULES( toprule );

static void ParamTest( const bp::symbols<double>& syms )
{
    auto result = bp::parse( "10.3", toprule.with( syms ), bp::ws );
}

By the way, am I correct that a rule must be defined at global scope?

See also a discussion on Stack Overflow, where a reply said "you're looking for lazy rule references" but I don't really know what that means.

[tzlaine]

I tried the following, and the compiler wasn't happy about it. I guess the tutorial's discussion of parameters was too complicated for me.

#include <boost/parser/parser.hpp>

namespace bp = ::boost::parser;

bp::rule< struct toprule, double > toprule = "toprule";
auto const toprule_def = bp::double_ >> bp::_p<0>;
BOOST_PARSER_DEFINE_RULES( toprule );

static void ParamTest( const bp::symbols& syms )
{
auto result = bp::parse( "10.3", toprule.with( syms ), bp::ws );
}

This is not a use case parameters are suited to; you can't pass parsers as parameters.

By the way, am I correct that a rule must be defined at global scope?

Almost. Namespace scope, not necessarily the global namespace.

See also a discussion on Stack Overflow, where a reply said "you're looking for lazy rule references" but I don't really know what that means.

Yeah, this came up in response to another request. I spent a really long time trying to figure out how to make a lazy rule work, but it's simply not possible given the current design.

The good news is that you're only real limitation is that, without lazy parsers, you cannot use a placeholder for one of an open set of possible parsers. However, you can still use one of a closed set of parsers by building the logic into your parser for which one to use, based on some parameterization.

For instance, you could write a parser that contains bp::if_(bp::_p<0>)[p1][p2] (or use bp::switch_ for more alternatives).