Restructure YAML package suitable for pub lish

utils/pub/yaml/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.
-
-part of yaml;
-
-/// 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.
-  _Node root;
-
-  /// Map from anchor names to the most recent Dart node with that anchor.
-  Map<String, dynamic> anchors;
-
-  _Constructor(this.root) : this.anchors = {};
-
-  /// Runs the Constructor to produce a Dart object.
-  construct() => root.visit(this);
-
-  /// Returns the value of a scalar.
-  visitScalar(_ScalarNode scalar) => scalar.value;
-
-  /// Converts a sequence into a List of Dart objects.
-  visitSequence(_SequenceNode seq) {
-    var anchor = getAnchor(seq);
-    if (anchor != null) return anchor;
-    var dartSeq = setAnchor(seq, []);
-    dartSeq.addAll(super.visitSequence(seq));
-    return dartSeq;
-  }
-
-  /// Converts a mapping into a Map of Dart objects.
-  visitMapping(_MappingNode map) {
-    var anchor = getAnchor(map);
-    if (anchor != null) return anchor;
-    var dartMap = setAnchor(map, new YamlMap());
-    super.visitMapping(map).forEach((k, v) { dartMap[k] = v; });
-    return dartMap;
-  }
-
-  /// Returns the Dart object that already represents [anchored], if such a
-  /// thing exists.
-  getAnchor(_Node anchored) {
-    if (anchored.anchor == null) return null;
-    if (anchors.containsKey(anchored.anchor)) return anchors[anchored.anchor];
-  }
-
-  /// Records that [value] is the Dart object representing [anchored].
-  setAnchor(_Node anchored, value) {
-    if (anchored.anchor == null) return value;
-    anchors[anchored.anchor] = value;
-    return value;
-  }
-}