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petitparser/lib/src/debug/trace.dart

-part of debug;
-
-/**
- * Returns a transformed [parser] that when being used to read input prints a
- * trace of all activated parsers and their respective parse results.
- *
- * For example, the snippet
- *
- *     var parser = letter() & word().star();
- *     trace(parser).parse('f1');
- *
- * produces the following output:
- *
- *     Instance of 'SequenceParser'
- *       Instance of 'CharacterParser'[letter expected]
- *       Success[1:2]: f
- *       Instance of 'PossessiveRepeatingParser'[0..*]
- *         Instance of 'CharacterParser'[letter or digit expected]
- *         Success[1:3]: 1
- *         Instance of 'CharacterParser'[letter or digit expected]
- *         Failure[1:3]: letter or digit expected
- *       Success[1:3]: [1]
- *     Success[1:3]: [f, [1]]
- *
- * Indentation signifies the activation of a parser object. Reverse indentation
- * signifies the returning of a parse result either with a success or failure
- * context.
- */
-Parser trace(Parser parser, [OutputHandler output = print]) {
-  var level = 0;
-  return transformParser(parser, (each) {
-    return new ContinuationParser(each, (continuation, context) {
-      output('${_repeat(level, '  ')}${each}');
-      level++;
-      var result = continuation(context);
-      level--;
-      output('${_repeat(level, '  ')}${result}');
-      return result;
-    });
-  });
-}