Call out precedence of `operator>` vs `operator>>` in docs (was: try parse url without scheme results in error)

[terrywh]

i was trying this nice library out, using the following code try to parse a url s with all of the parts optional except the host part:

#include <boost/parser/parser.hpp>
#include <iostream>

namespace bp = boost::parser;
using namespace std::string_literals;

int main(int argc, char* argv[]) {
    // auto url = "https://www.qq.com:443/abc/123?a=b&c=d"s;
    auto url = "www.qq.com"s;
    if (argc > 1) {
        url = argv[1];
    }
    auto begin = url.begin();
    auto result = bp::prefix_parse(begin, url.end(),
        bp::eps
        >> - (+(bp::char_ - ':') > "://") // an "optional" resulting the error ?
        >> + (bp::char_ - ':' - '/' - '?')
        >> - (':' >> bp::int_)
        >> - ('/' >> +(bp::char_ - '?'))
        >> - ('?' >> +bp::char_));
    if (result) {
        auto scheme = std::get<0>(result.value());
        if (scheme) {
            std::cout << "scheme: " << scheme.value() << std::endl;
        }

        auto host = std::get<1>(result.value());
        std::cout << "host: " << host << std::endl;

        auto port = std::get<2>(result.value());
        if (port) {
            std::cout << "port: " << port.value() << std::endl;
        }

        auto path = std::get<3>(result.value());
        if (path) {
            std::cout << "path: " << path.value() << std::endl;
        }

        auto query = std::get<4>(result.value());
        if (query) {
            std::cout << "query: " << query.value() << std::endl;
        }
    }
    return 0;
}

if i understand correcly, the operator - allows an optional matching; but instead after running i get this error output:

1:10: error: Expected "://" here (end of input):
www.qq.com
          ^

parsing a url like 'www.qq.com?a=b' will result the following:

1:14: error: Expected "://" here (end of input):
www.qq.com?abc'

maybe i'm using it wrong ?

[terrywh]

Change

>> - (+(bp::char_ - ':') > "://")

To

>> - (+(bp::char_ - ':') >> "://")

solved the problem, i guess ">" has a higher priority than "-". closing this for now.

[tzlaine]

This needs to be called out in the docs so this doesn't happen to more people.