Restructure the yaml package.

pkg/yaml/lib/src/composer.dart

Index: pkg/yaml/lib/src/composer.dart
diff --git a/pkg/yaml/lib/composer.dart b/pkg/yaml/lib/src/composer.dart
similarity index 71%
rename from pkg/yaml/lib/composer.dart
rename to pkg/yaml/lib/src/composer.dart
index 90ed3308eddc1bdb5a57002aa3b01d2bfbeaa855..40b76677e654a760c25f88ce8c66d393a9012c1e 100644
--- a/pkg/yaml/lib/composer.dart
+++ b/pkg/yaml/lib/src/composer.dart
@@ -2,41 +2,45 @@
 // 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;
+library composer;
+
+import 'model.dart';
+import 'visitor.dart';
+import 'yaml_exception.dart';
 
 /// Takes a parsed YAML document (what the spec calls the "serialization tree")
 /// and resolves aliases, resolves tags, and parses scalars to produce the
 /// "representation graph".
-class _Composer extends _Visitor {
+class Composer extends Visitor {
   /// The root node of the serialization tree.
-  _Node root;
+  final Node _root;
 
   /// Map from anchor names to the most recent representation graph node with
   /// that anchor.
-  Map<String, _Node> anchors;
+  final _anchors = <String, Node>{};
 
   /// The next id to use for the represenation graph's anchors. The spec doesn't
   /// use anchors in the representation graph, but we do so that the constructor
   /// can ensure that the same node in the representation graph produces the
   /// same native object.
-  int idCounter;
+  var _idCounter = 0;
 
-  _Composer(this.root) : this.anchors = <String, _Node>{}, this.idCounter = 0;
+  Composer(this._root);
 
   /// Runs the Composer to produce a representation graph.
-  _Node compose() => root.visit(this);
+  Node compose() => _root.visit(this);
 
   /// Returns the anchor to which an alias node refers.
-  _Node visitAlias(_AliasNode alias) {
-    if (!anchors.containsKey(alias.anchor)) {
+  Node visitAlias(AliasNode alias) {
+    if (!_anchors.containsKey(alias.anchor)) {
       throw new YamlException("no anchor for alias ${alias.anchor}");
     }
-    return anchors[alias.anchor];
+    return _anchors[alias.anchor];
   }
 
   /// Parses a scalar node according to its tag, or auto-detects the type if no
   /// tag exists. Currently this only supports the YAML core type schema.
-  _Node visitScalar(_ScalarNode scalar) {
+  Node visitScalar(ScalarNode scalar) {
     if (scalar.tag.name == "!") {
       return setAnchor(scalar, parseString(scalar.content));
     } else if (scalar.tag.name == "?") {
@@ -54,7 +58,7 @@ class _Composer extends _Visitor {
     };
 
     for (var key in tagParsers.keys) {
-      if (scalar.tag.name != _Tag.yaml(key)) continue;
+      if (scalar.tag.name != Tag.yaml(key)) continue;
       var result = tagParsers[key](scalar.content);
       if (result != null) return setAnchor(scalar, result);
       throw new YamlException('invalid literal for $key: "${scalar.content}"');
@@ -64,69 +68,69 @@ class _Composer extends _Visitor {
   }
 
   /// Assigns a tag to the sequence and recursively composes its contents.
-  _Node visitSequence(_SequenceNode seq) {
+  Node visitSequence(SequenceNode seq) {
     var tagName = seq.tag.name;
-    if (tagName != "!" && tagName != "?" && tagName != _Tag.yaml("seq")) {
+    if (tagName != "!" && tagName != "?" && tagName != Tag.yaml("seq")) {
       throw new YamlException("invalid tag for sequence: ${tagName}");
     }
 
-    var result = setAnchor(seq, new _SequenceNode(_Tag.yaml("seq"), null));
+    var result = setAnchor(seq, new SequenceNode(Tag.yaml("seq"), null));
     result.content = super.visitSequence(seq);
     return result;
   }
 
   /// Assigns a tag to the mapping and recursively composes its contents.
-  _Node visitMapping(_MappingNode map) {
+  Node visitMapping(MappingNode map) {
     var tagName = map.tag.name;
-    if (tagName != "!" && tagName != "?" && tagName != _Tag.yaml("map")) {
+    if (tagName != "!" && tagName != "?" && tagName != Tag.yaml("map")) {
       throw new YamlException("invalid tag for mapping: ${tagName}");
     }
 
-    var result = setAnchor(map, new _MappingNode(_Tag.yaml("map"), null));
+    var result = setAnchor(map, new MappingNode(Tag.yaml("map"), null));
     result.content = super.visitMapping(map);
     return result;
   }
 
   /// If the serialization tree node [anchored] has an anchor, records that
   /// that anchor is pointing to the representation graph node [result].
-  _Node setAnchor(_Node anchored, _Node result) {
+  Node setAnchor(Node anchored, Node result) {
     if (anchored.anchor == null) return result;
-    result.anchor = '${idCounter++}';
-    anchors[anchored.anchor] = result;
+    result.anchor = '${_idCounter++}';
+    _anchors[anchored.anchor] = result;
     return result;
   }
 
   /// Parses a null scalar.
-  _ScalarNode parseNull(String content) {
+  ScalarNode parseNull(String content) {
     if (!new RegExp(r"^(null|Null|NULL|~|)$").hasMatch(content)) return null;
-    return new _ScalarNode(_Tag.yaml("null"), value: null);
+    return new ScalarNode(Tag.yaml("null"), value: null);
   }
 
   /// Parses a boolean scalar.
-  _ScalarNode parseBool(String content) {
+  ScalarNode parseBool(String content) {
     var match = new RegExp(r"^(?:(true|True|TRUE)|(false|False|FALSE))$").
       firstMatch(content);
     if (match == null) return null;
-    return new _ScalarNode(_Tag.yaml("bool"), value: match.group(1) != null);
+    return new ScalarNode(Tag.yaml("bool"), value: match.group(1) != null);
   }
 
   /// Parses an integer scalar.
-  _ScalarNode parseInt(String content) {
+  ScalarNode parseInt(String content) {
     var match = new RegExp(r"^[-+]?[0-9]+$").firstMatch(content);
     if (match != null) {
-      return new _ScalarNode(_Tag.yaml("int"),
+      return new ScalarNode(Tag.yaml("int"),
           value: int.parse(match.group(0)));
     }
 
     match = new RegExp(r"^0o([0-7]+)$").firstMatch(content);
     if (match != null) {
       int n = int.parse(match.group(1), radix: 8);
-      return new _ScalarNode(_Tag.yaml("int"), value: n);
+      return new ScalarNode(Tag.yaml("int"), value: n);
     }
 
     match = new RegExp(r"^0x[0-9a-fA-F]+$").firstMatch(content);
     if (match != null) {
-      return new _ScalarNode(_Tag.yaml("int"),
+      return new ScalarNode(Tag.yaml("int"),
           value: int.parse(match.group(0)));
     }
 
@@ -134,7 +138,7 @@ class _Composer extends _Visitor {
   }
 
   /// Parses a floating-point scalar.
-  _ScalarNode parseFloat(String content) {
+  ScalarNode parseFloat(String content) {
     var match = new RegExp(
         r"^[-+]?(\.[0-9]+|[0-9]+(\.[0-9]*)?)([eE][-+]?[0-9]+)?$").
       firstMatch(content);
@@ -142,25 +146,25 @@ class _Composer extends _Visitor {
       // YAML allows floats of the form "0.", but Dart does not. Fix up those
       // floats by removing the trailing dot.
       var matchStr = match.group(0).replaceAll(new RegExp(r"\.$"), "");
-      return new _ScalarNode(_Tag.yaml("float"),
+      return new ScalarNode(Tag.yaml("float"),
           value: double.parse(matchStr));
     }
 
     match = new RegExp(r"^([+-]?)\.(inf|Inf|INF)$").firstMatch(content);
     if (match != null) {
       var value = match.group(1) == "-" ? -double.INFINITY : double.INFINITY;
-      return new _ScalarNode(_Tag.yaml("float"), value: value);
+      return new ScalarNode(Tag.yaml("float"), value: value);
     }
 
     match = new RegExp(r"^\.(nan|NaN|NAN)$").firstMatch(content);
     if (match != null) {
-      return new _ScalarNode(_Tag.yaml("float"), value: double.NAN);
+      return new ScalarNode(Tag.yaml("float"), value: double.NAN);
     }
 
     return null;
   }
 
   /// Parses a string scalar.
-  _ScalarNode parseString(String content) =>
-    new _ScalarNode(_Tag.yaml("str"), value: content);
+  ScalarNode parseString(String content) =>
+    new ScalarNode(Tag.yaml("str"), value: content);
 }