Get any rule's value as a string

[0x0015]

Hello,

I was wondering if there is a way that for any rule that has been matched, to return the value of whatever string was matched, rather than what other value type that should be returned.

Two examples (one over simplified, and one more actual use-case-y):

A boolean parser (yes this is not generally how you would actually want to do this, and rather have a separate parser for true and false)

struct boolean{
	static constexpr auto rule = LEXY_LIT("true") | LEXY_LIT("false");
	static constexpr auto value = lexy::callback<bool>([](const auto& lx){
		std::string s(lx.begin(), lx.end());
		return s == "true";
	});
	//value = lexy::as_string<std::string>; //also doesn't work
	//if it did, I could (I think) do:  value = lexy::as_string<std::string> >> lexy::callback(.......)
};

and a more realistic example of trying to parse a decimal

struct decimal{
	static constexpr auto rule = dsl::sign + dsl::digits<> + dsl::period + dsl::digits<>;
	static constexpr auto value = lexy::callback<float>([](const auto& lx){
		std::string s(lx.begin(), lx.end());
		return std::stof(s);
	});

};

[foonathan]

You want dsl::capture.

[aglie]

Sorry, I still don't understand. I am trying to capture ints as a string and fail to do so:

#include <lexy/action/parse.hpp>
#include <lexy/input/string_input.hpp>
#include <lexy/callback.hpp>
#include <lexy/dsl.hpp>
#include <lexy_ext/report_error.hpp>
#include <lexy_ext/compiler_explorer.hpp>
#include <iostream>

using namespace lexy;

// Define the production for an integer
//using lexeme = lexy_ext::compiler_explorer_lexeme;
struct integer : lexy::token_production
{
    // Define the rule to match a sequence of digits
    static constexpr auto rule = lexy::dsl::capture(lexy::dsl::digits<>);

        // Same as `lexy::as_string<std::string>`.
        static constexpr auto value = lexy::callback<std::string>(
                [](lexy_ext::compiler_explorer_lexeme lex)
                { return std::string(lex.begin(), lex.end()); });
};

int main()
{
    // Input string containing an integer
    auto input = lexy::zstring_input("123");

    // Parse the input using the 'integer' production
    auto result = lexy::parse<integer>(input, lexy_ext::report_error);

    // Check if parsing was successful
    if (result)
        std::cout << "Matched string: " << result.value() << '\n';
    else
        std::cerr << "Failed to parse integer.\n";

    return 0;
}

Which fails to compile on the line with parse<integer> with the error

 error: static_assert failed due to requirement '_detail::error<integer, lexy::lexeme<lexy::_prd> >' "missing value callback overload for production"
            static_assert(_detail::error<Production, Args...>,

[foonathan]

lexy_ext::compiler_error_lexeme is the lexeme type when you use lexy_ext::compiler_explorer_input(). You're using lexy::zstring_input though whose lexeme type is lexy::string_lexeme<>: https://lexy.foonathan.net/reference/input/string_input/#typedefs If you want to support multiple inputs, make the lambda generic and accept auto lex or []<typename Reader>(lexy::lexeme<Reader> lex). If you only want to convert a lexeme to a string, use lexy::as_string: https://lexy.foonathan.net/reference/callback/string/#as_string