anchor.diff:      });
       test('expression example', () {
         final definition = ExpressionGrammarDefinition();
  -      final parser = GrammarParser(definition);
  +      final parser = definition.build();
         expect(parser.accept('1'), isTrue);
         expect(parser.accept('12'), isTrue);
         expect(parser.accept('1.23'), isTrue);
  
positive.code:       expect(parser.accept('(1 + 2) * 3'), isTrue);
      });
    });
  }
  
negative.code: import 'package:petitparser/petitparser.dart';
  import 'package:test/test.dart';
  
  import 'parser_test.dart';
  import 'test_utils.dart';
  
  class ListGrammarDefinition extends GrammarDefinition {
  