progress<R> function

  1. @useResult
Parser<R> progress<R>(
  1. Parser<R> root, {
  2. VoidCallback<ProgressFrame> output = print,
  3. Predicate<Parser>? predicate,
})

Returns a transformed Parser that when being used to read input visually prints its progress while progressing.

For example, the snippet

final parser = letter() & word().star(); progress(parser).parse('f123');

prints the following output:

* SequenceParser * SingleCharacterParser[letter expected] ** PossessiveRepeatingParser[0..*] ** SingleCharacterParser[letter or digit expected] *** SingleCharacterParser[letter or digit expected] **** SingleCharacterParser[letter or digit expected] ***** SingleCharacterParser[letter or digit expected]

Jumps backwards mean that the parser is back-tracking. Often choices can be reordered to avoid such expensive parses.

The optional output callback can be used to continuously receive ProgressFrame updates with the current progress information.

Implementation

@useResult Parser<R> progress<R>( Parser<R> root, { VoidCallback<ProgressFrame> output = print, Predicate<Parser>? predicate, }) => transformParser(root, <P>(parser) { if (predicate == null || predicate(parser)) { return parser.callCC((continuation, context) { output(_ProgressFrame(parser, context)); return continuation(context); }); } else { return parser; } });