I'm writing a parser in Spirit X3 in order to get familiar with it, and even though I'm pretty familiar Qi I'm still hitting some stumbling blocks in X3.
For example, the Qi examples include a basic XML parser that should you how to match a previously matched value using Phoenix placeholders. However, I've only kinda been able to figure it out in X3:
#include <iostream>
#include <boost/spirit/home/x3.hpp>
#include <boost/fusion/include/adapt_struct.hpp>
namespace x3 = boost::spirit::x3;
namespace mytest
{
struct SimpleElement
{
std::string tag;
std::string content;
};
} // namespace bbspirit
BOOST_FUSION_ADAPT_STRUCT
(
mytest::SimpleElement, tag, content
)
namespace mytest
{
namespace x3 = boost::spirit::x3;
namespace ascii = boost::spirit::x3::ascii;
using x3::lit;
using x3::lexeme;
using ascii::char_;
const x3::rule<class SimpleElementID, SimpleElement> simpleTag = "simpleTag";
auto assignTag = [](auto& ctx)
{
x3::_val(ctx).tag = x3::_attr(ctx);
};
auto testTag = [](auto& ctx)
{
x3::_pass(ctx) =
(x3::_val(ctx).tag == x3::_attr(ctx));
};
auto assignContent = [](auto& ctx)
{
x3::_val(ctx).content = x3::_attr(ctx);
};
auto const simpleTag_def
= '['
>> x3::lexeme[+(char_ - ']')][assignTag]
>> ']'
>> x3::lexeme[
+(char_ - x3::lit("[/"))]
[assignContent]
>> "[/"
>> x3::lexeme[+(char_ - ']')][testTag]
>> ']'
;
BOOST_SPIRIT_DEFINE(simpleTag);
} // namespace bbspirit
int main()
{
const std::string text = "[test]Hello World![/test]";
std::string::const_iterator start = std::begin(text);
const std::string::const_iterator stop = std::end(text);
mytest::SimpleElement element{};
bool result =
phrase_parse(start, stop, mytest::simpleTag, x3::ascii::space, element);
if (!result)
{
std::cout << "failed to parse!\n";
}
else
{
std::cout << "tag : " << element.tag << '\n';
std::cout << "content: " << element.content << '\n';
}
}
(Link: https://wandbox.org/permlink/xLZN9plcOwkSKCrD )
This works, however if I try to parse something like [test]Hello [/World[/test] it doesn't work because I have not specified the correct omission here:
>> x3::lexeme[
+(char_ - x3::lit("[/"))]
[assignContent]
Essentially I want to tell the parser something like:
>> x3::lexeme[
+(char_ - (x3::lit("[/") << *the start tag* << ']') )]
[assignContent]
How could I go about doing this? Also, is the way in which I'm referencing the start tag and later matching it the "best" way to do this in X3 or is there a better/more preferred way?
Thank you!
