Question: an analog of Positioned from Sprache?

In Sprache, you provided IPositionAware and Positioned to make a parse result, well, aware of the position it’s parsed. I see this feature useful for giving a precise position of some syntax construct in post-parse checks (like, “this variable right here wasn’t declared” vs. the same without being able to report a position to the user, so they would have to search that place for themselves).

There is Result<T>.Location, but I don’t see how I could apply that to the resulting value via combinators. Could I achive it here, and which way you’d advice to do it best? (Or if maybe I’m looking for the wrong thing, and the thing mentioned should be done another way.)

[nblumhardt]

Hi!

There’s no built-in combinator; I think it would be reasonably easy to write one, using similar tactics to Sprache’s implementation - keen to explore how it might look.

If you want to drop this into your own project I think it’s roughly:

interface ILocated
{
    TextSpan Location { get; set; }
}

static TextParser<T> WithLocation<T>(this TextParser<T> parser)
    where T: ILocated
{
    return i => {
        var inner = parser(i);
        if (!inner.HasValue) return inner;
        inner.Value.Location = inner.Location;
        return inner;
    };
}

(Sketched in browser, no idea whether or not this will compile as-is 😉)

HTH, Nick

[nblumhardt]

Hi @JoeMGomes - unfortunately no time to dig in properly but hopefully this helps:

The start index of the match within the input will be inner.Location.First().Position.Absolute.

The exclusive end index will be inner.Remainder.First().Position.Absolute.

In the second case it’s also possible that the remainder token list will be empty, which would mean “matched until end of stream”.