petitparser is a parser generator written in dart to be used e.g. in Flutter.
According to this page, petitparser allows to use ref0 to reference the current parse class.
In the section Using Grammar Definitions you read this statement:
To refer to a production defined in the same definition use [ref0] with the function reference as the argument.
According to the docs, you have to define this dependecy to the petitpackage package
dependencies:
petitparser: ^4.0.2
and include this:
import 'package:petitparser/petitparser.dart';
Unfortunately, ref0 and ref1 do not resolve. Why?
In case the package and the sources are out of sync: Does a simple way to replace ref0 by equivalent valid code exist?
Additionally, I didn't find ref0 / ref1 in the API-documentation.
You are referring to the documentation on GitHub, which is the development version of PetitParser (that is the upcoming version of PetitParser 4.1.0). Please refer to the documentation of the PetitParser version you have installed, i.e https://pub.dev/packages/petitparser/versions/4.0.2.
Regarding your question: Unfortunately 4.0.2 did not document ParserDefinition in the tutorial. If you read the latest documentation you can replace all references of ref0, ref1, ... with ref. The number suffix was added for 4.1.0 to allow stricter typing.