How to listen to the parsed result immediately?

[dhaval15]

I want to parse file that has metadata on top, and I want to parse that metadata and populate that data to parse the rest of file ? How would I do that. As far as I understand the map function is called on second pass after successful parsing. So with MapParser I couldn't achieve that or am I missing something ?

[renggli]

Probably the easiest is if you split this into two separate parsing steps: You can use the Result of the meta-data parser to build the data parser, as well as to resume the parse where the meta-data parser completed. Something along these lines:

final metadataResult = metadataParser.parse(input);
final dataParser = buildDataParser(metadataResult.value);
final dataResult = dataParser.parseOn(metadataResult);

Alternatively you can use the ContinuationParser to merge this into a single parser that returns the result of the data parser:

final parser = metadataParser.callCC((continuation, context) {
  final metadataResult = continuation(context);
  final dataParser = buildDataParser(metadataResult.value);
  return dataParser.parseOn(metadataResult);
});

[renggli]

To also answer your question about the map function: It is immediately called if the inner parser succeeds. There is no second pass, everything is done in a single pass.

[dhaval15]

Probably the easiest is if you split this into two separate parsing steps: You can use the Result of the meta-data parser to build the data parser, as well as to resume the parse where the meta-data parser completed. Something along these lines:

final metadataResult = metadataParser.parse(input);
final dataParser = buildDataParser(metadataResult.value);
final dataResult = dataParser.parseOn(metadataResult);

Alternatively you can use the ContinuationParser to merge this into a single parser that returns the result of the data parser:

final parser = metadataParser.callCC((continuation, context) {
  final metadataResult = continuation(context);
  final dataParser = buildDataParser(metadataResult.value);
  return dataParser.parseOn(metadataResult);
});

Thanks, the first approach worked.