Acquire line number at the point of the rule

[matejk]

Lexy is used to write a parser to read line-oriented syntax: each line can contain a different set of value/pair items. Lines are then processed like this:

    struct nc_file
    {
        static constexpr auto whitespace = dsl::ascii::space;
        static constexpr auto rule = [] {
            auto line = dsl::p<nc_line>;

            auto terminator = dsl::terminator(dsl::eof);
            return terminator.list(line);
        }();

        static constexpr auto value = lexy::as_list<std::vector<item_vector>>;
    };

I want to save the line number for each of the lines that are read. From the documentation of input_location::line_nr(), however I don't know how to use it in the rule or whether that is proper way to get the line number.

[foonathan]

The way it's supposed to work is that you use the rule dsl::position which gives you an iterator into the input, then later call lexy::get_input_location() to convert the iterators into line/column numbers.

However, in your particular case, it is probably easier if you use dsl::context_counter: create one in your nr_file rule, increment it after every line and use .value() to get the line number during parsing.

[natinusala]

I'm replying to this thread instead of making a new one because my question is related - if I have a rule like this: LEXY_LIT("if") >> dsl::p<...>

I can do this to get the position: LEXY_LIT("if") >> dsl::position + dsl::p<...>

But what if I want the position before the if, do I need to use peek? dsl::peek(LEXY_LIT("if")) >> dsl::position + LEXY_LIT("if") + dsl::p<...>

Is this the intended way?

[foonathan]

Either do the dsl::position in the rule that has the choice (i.e.: dsl::position + (dsl::p<if_stmt> | ... ))) or use dsl::capture(LEXY_LIT("if")) >> ..., but note that it gives you a lexeme where you have to manually instruct the position with .begin(): https://lexy.foonathan.net/reference/dsl/capture/#capture