How to parse into string a small token with a constraining pattern?

[akrzemi1]

Boost.Spirit allowed the syntax for defining a parser that matched a token compliant with a simple pattern and had a `std::string as attribute:

auto myParser  = (alpha >> alpha >> -alnum);

Does Boost.Parser offer an equivalent?

Here is a full code that compiles in Boost.Spirit but not in Boost.Parser. You already said Boost.Parser will not provide an identical syntax, so I am asking for an alternative.

#ifdef WITH_BOOST_SPIRIT
#include <boost/fusion/adapted/struct/adapt_struct.hpp>
#include <boost/spirit/include/qi.hpp>
namespace bp = boost::spirit::qi;
#else
#include <boost/parser/parser.hpp>
namespace bp = boost::parser;
#endif

int main()
{
#ifdef WITH_BOOST_SPIRIT
  auto alnum = bp::ascii::alnum;
  auto alpha = bp::alpha;
#else
  auto alnum = bp::ascii::alnum;
  auto alpha = bp::ascii::alpha;
#endif

  auto myParser  = (alpha >> alpha >> -alnum);

  std::string input = "MM2";
  std::string result;

#ifdef WITH_BOOST_SPIRIT
  auto begin = input.begin();
  bool b = bp::phrase_parse(begin, input.end(), myParser, bp::ascii::space, result);
#else
  auto b = bp::parse(input, myParser, bp::ws, result);
#endif

  if (b)
    std::cout << ":-) " << result << std::endl;
  else
    std::cout << ":-(" << std::endl;
}

[tzlaine]

Remember the thing I said before on #50 (https://github.com/tzlaine/parser/issues/50#issuecomment-1879827991)? I think that applies to my example of parsing ints, but far less so to parsing individual characters. Just like I have as special case for std::string instead of std::vector<char> in repeat parsers, I'm now considering a special case for char types in sequence parsers.

I have this in mind:

1) The example above would produce a std::string. 2) Introduce separate[] directive (which would apply only to sequence parsers) to disable combining, like how it would happen under 1), or in general, like it happens now for *int_ >> int_. 3) Introduce merge[] (also only for sequence parsers) that would make the int_ >> int_ attribute std::vector<int>.

I'm still wrestling with the idea of including char32_t-attribute parsers in 1) and in the current std::string versus std::vector rule. I'm leading toward inclusion; I think it's more natural not to have to worry about the distinction.