packages/petitparser/lib/src/debug/continuation.dart

part of petitparser.debug;

/// Handler function for the [ContinuationParser].
typedef Result ContinuationHandler(
    Result continuation(Context context), Context context);

/// Continuation parser that when activated captures a continuation function
/// and passes it together with the current context into the handler.
///
/// Handlers are not required to call the continuation, but can completely ignore
/// it, call it multiple times, and/or store it away for later use. Similarly
/// handlers can modify the current context and/or modify the returned result.
///
/// The following example shows a simple wrapper. Messages are printed before and
/// after the `digit()` parser is activated:
///
///     var wrapped = digit();
///     var parser = new ContinuationParser(wrapped, (continuation, context) {
///       print('Parser will be activated, the context is $context.');
///       var result = continuation(context);
///       print('Parser was activated, the result is $result.');
///       return result;
///     });
///
/// See [profile], [progress], and [trace] for more elaborate examples.
class ContinuationParser extends DelegateParser {
  final ContinuationHandler handler;

  ContinuationParser(parser, this.handler) : super(parser);

  @override
  Result parseOn(Context context) {
    return handler((result) => super.parseOn(result), context);
  }

  @override
  Parser copy() => new ContinuationParser(children[0], handler);
}