Position of the match

[RomanSoloweow]

Can I find out the position where the match was found?

[tomtheisen]

If you're writing a parser, you can get the current position using the Position property of the input (IInput). If you're not writing a parser, you might need to start. If I'm not mistaken, that's the only way to do it.

[yallie]

@RomanSoloweow,

Use Span() modifier to return the starting and ending positions of the parsed item.
Example:

var parser =
    from leading in Parse.WhiteSpace.Many()
    from span in Parse.Identifier(Parse.Letter, Parse.LetterOrDigit).Span()
    from trailing in Parse.WhiteSpace.Many()
    select span;

var r = parser.TryParse("  Hello!");
var id = r.Value;
Assert.Equal("Hello", id.Value);
Assert.Equal(5, id.Length);

// span.Start is the starting position
Assert.Equal(2, id.Start.Pos);
Assert.Equal(1, id.Start.Line);
Assert.Equal(3, id.Start.Column);

// span.End is the ending position
Assert.Equal(7, id.End.Pos);
Assert.Equal(1, id.End.Line);
Assert.Equal(8, id.End.Column);

[yallie]

Parse.Span return value looks like this:

public interface ITextSpan<T>
{
    T Value { get; }
    Position Start { get; }
    Position End { get; }
    int Length { get; }
}

[RomanSoloweow]

Is there an example of how to use it?
I need to check for matches and, if successful, return the position of the matches found

[yallie]

Just append .Span() to any existing parser like I posted before:

var parser =
    from leading in Parse.WhiteSpace.Many()
    from span in Parse.Identifier(Parse.Letter, Parse.LetterOrDigit).Span() // <- here
    from trailing in Parse.WhiteSpace.Many()
    select span;

The parser above will return ITextSpan<string> instead of just string.
So you'll get the parsed value with the position and length of its span.
For more examples, please check out the unit tests in this repository.