Rewrite the pkg/yaml parser.

pkg/yaml/lib/src/constructor.dart

-// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-library yaml.constructor;
-
-import 'equality.dart';
-import 'model.dart';
-import 'visitor.dart';
-import 'yaml_node.dart';
-
-/// Takes a parsed and composed YAML document (what the spec calls the
-/// "representation graph") and creates native Dart objects that represent that
-/// document.
-class Constructor extends Visitor {
-  /// The root node of the representation graph.
-  final Node _root;
-
-  /// Map from anchor names to the most recent Dart node with that anchor.
-  final _anchors = <String, YamlNode>{};
-
-  Constructor(this._root);
-
-  /// Runs the Constructor to produce a Dart object.
-  YamlNode construct() => _root.visit(this);
-
-  /// Returns the value of a scalar.
-  YamlScalar visitScalar(ScalarNode scalar) =>
-      new YamlScalar.internal(scalar.value, scalar.span);
-
-  /// Converts a sequence into a List of Dart objects.
-  YamlList visitSequence(SequenceNode seq) {
-    var anchor = getAnchor(seq);
-    if (anchor != null) return anchor;
-    var nodes = [];
-    var dartSeq = setAnchor(seq, new YamlList.internal(nodes, seq.span));
-    nodes.addAll(super.visitSequence(seq));
-    return dartSeq;
-  }
-
-  /// Converts a mapping into a [Map] of Dart objects.
-  YamlMap visitMapping(MappingNode map) {
-    var anchor = getAnchor(map);
-    if (anchor != null) return anchor;
-    var nodes = deepEqualsMap();
-    var dartMap = setAnchor(map, new YamlMap.internal(nodes, map.span));
-    super.visitMapping(map).forEach((k, v) => nodes[k] = v);
-    return dartMap;
-  }
-
-  /// Returns a new Dart object wrapping the object that already represents
-  /// [anchored], if such a thing exists.
-  YamlNode getAnchor(Node anchored) {
-    if (anchored.anchor == null) return null;
-    var value = _anchors[anchored.anchor];
-    if (value == null) return null;
-
-    // Re-wrap [value]'s contents so that it's associated with the span of the
-    // anchor rather than its original definition.
-    if (value is YamlMap) {
-      return new YamlMap.internal(value.nodes, anchored.span);
-    } else if (value is YamlList) {
-      return new YamlList.internal(value.nodes, anchored.span);
-    } else {
-      assert(value is YamlScalar);
-      return new YamlScalar.internal(value.value, anchored.span);
-    }
-  }
-
-  /// Records that [value] is the Dart object representing [anchored].
-  YamlNode setAnchor(Node anchored, YamlNode value) {
-    if (anchored.anchor == null) return value;
-    _anchors[anchored.anchor] = value;
-    return value;
-  }
-}