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

lib/yaml/yaml.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");
+
+#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) {
+  var tok = new _Parser(yaml);
+  return tok._l_yamlStream().map((doc) =>
+      new _Constructor(new _Composer(doc).compose()).construct());
+}
+
+/** An error thrown by the YAML processor. */
+class Error implements Exception {

[Bob Nystrom, 2012/04/20 20:28:55]

"YamlException"

[nweiz, 2012/04/23 23:06:33]

I expect people to implement this library with a prefix (hence the generic
top-level names like "load"). "yaml.YamlException" feels awkward and redundant.

[Bob Nystrom, 2012/04/24 00:50:36]

Hmm, we should discuss this offline. So far, we very rarely use prefixes and
don't see to design our libraries assuming users will use them.

[nweiz, 2012/04/25 00:26:29]

Done, although I'd rather see a more principled namespace system.

+  String _msg;
+
+  Error(String this._msg);
+
+  String toString() => _msg;
+}