Boost Spirit nested components

Question

I am trying to parse the following messages with Spirit Qi:

"A/B AND C/D", "A/B", "A/B AND C/D AND E/F"

I am able to parse "A/B" but cannot get the correct results for the other strings.

I tried to following code:

qi::rule<It, AstNodeVector()> entries;
qi::rule<It, AstNodeVector()> lists;
qi::rule<It, std::string()> element;

this->entries= *(this->lists % " AND ");
this->lists= this->element >> '/' >> this->element;
this->element = qi::char_("A-Z");

What is wrong with my grammar?

sehe sehe · Accepted Answer · 2021-02-19T20:40:54

It seems you're not skipping whitespace. Maybe that's a conceptual problem (see Boost spirit skipper issues).

Regardless, it does parse:

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#include <boost/spirit/include/qi.hpp>
#include <iomanip>
namespace qi = boost::spirit::qi;

using AstNodeVector = std::vector<std::string>;

template <typename It>
struct P : qi::grammar<It, AstNodeVector()> {
    P() : P::base_type(entries) {
        entries = *(lists % " AND ");
        lists   = element >> '/' >> element;
        element = qi::char_("A-Z");
    }
  private:
    qi::rule<It, AstNodeVector()> entries;
    qi::rule<It, AstNodeVector()> lists;
    qi::rule<It, std::string()> element;
};

int main() {
    using It = std::string::const_iterator;
    P<It> const p {};

    for (std::string const input: {
        "A/B AND C/D",
        "A/B",
        "A/B AND C/D AND E/F",
        })
    {
        It f = begin(input), l = end(input);
        AstNodeVector results;
        if (phrase_parse(f, l, p, qi::space, results)) {
            std::cout << "Success: " << std::quoted(input) << "\n";
            for (auto& el : results) {
                std::cout << " -- " << std::quoted(el) << "\n";
            }
        } else {
            std::cout << "FAIL: " << std::quoted(input) << "\n";
        }

        if (f != l) {
            std::cout << "Remaining input: " << std::quoted(std::string(f,l)) << "\n";
        }
    }
}

Prints

Success: "A/B AND C/D"
 -- "A"
 -- "B"
 -- "C"
 -- "D"
Success: "A/B"
 -- "A"
 -- "B"
Success: "A/B AND C/D AND E/F"
 -- "A"
 -- "B"
 -- "C"
 -- "D"
 -- "E"
 -- "F"

Perhaps you should have included self-contained code, or elaborate on what exactly is the problem.

Boost Spirit nested components

1 Answers