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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);
+}