Add a basic YAML processor. Much of the language is still unimplemented.

utils/yaml/yaml.dart

Index: utils/yaml/yaml.dart
diff --git a/utils/yaml/yaml.dart b/utils/yaml/yaml.dart
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+++ b/utils/yaml/yaml.dart
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+// 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");
+
+#import("deep_equals.dart");
+
+#source("yaml_map.dart");
+#source("model.dart");
+#source("parser.dart");
+#source("visitor.dart");
+#source("composer.dart");
+#source("constructor.dart");
+
+/**
+ * Loads a single document from a YAML string. If the string contains more than
+ * one document, this throws an error.
+ *
+ * The return value is mostly normal Dart objects. However, since YAML mappings
+ * support some key types that the default Dart map implementation doesn't
+ * (null, NaN, booleans, lists, and maps), all maps in the returned document are
+ * YamlMaps. These have a few small behavioral differences from the default Map
+ * implementation; for details, see the YamlMap class.
+ */
+load(String yaml) {
+  var stream = loadStream(yaml);
+  if (stream.length != 1) {
+    throw new Error("Expected 1 document, were ${stream.length}");
+  }
+  return stream[0];
+}
+
+/**
+ * Loads a stream of documents from a YAML string.
+ *
+ * The return value is mostly normal Dart objects. However, since YAML mappings
+ * support some key types that the default Dart map implementation doesn't
+ * (null, NaN, booleans, lists, and maps), all maps in the returned document are
+ * YamlMaps. These have a few small behavioral differences from the default Map
+ * implementation; for details, see the YamlMap class.
+ */
+List loadStream(String yaml) {
+  return new _Parser(yaml).l_yamlStream().map((doc) =>
+      new _Constructor(new _Composer(doc).compose()).construct());
+}
+
+/** An error thrown by the YAML processor. */
+class Error implements Exception {
+  String msg;
+
+  Error(this.msg);
+
+  String toString() => msg;
+}