Rewrite the pkg/yaml parser.

pkg/yaml/lib/src/style.dart

+// Copyright (c) 2014, 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.style;
+
+/// An enum of source scalar styles.
+class ScalarStyle {
+  /// No source style was specified.
+  ///
+  /// This usually indicates a scalar constructed with [YamlScalar.wrap].
+  static const ANY = const ScalarStyle._("ANY");
+
+  /// The plain scalar style, unquoted and without a prefix.
+  ///
+  /// See http://yaml.org/spec/1.2/spec.html#style/flow/plain.
+  static const PLAIN = const ScalarStyle._("PLAIN");
+
+  /// The literal scalar style, with a `|` prefix.
+  ///
+  /// See http://yaml.org/spec/1.2/spec.html#id2795688.
+  static const LITERAL = const ScalarStyle._("LITERAL");
+
+
+  /// The folded scalar style, with a `>` prefix.
+  ///
+  /// See http://yaml.org/spec/1.2/spec.html#id2796251.
+  static const FOLDED = const ScalarStyle._("FOLDED");
+
+  /// The single-quoted scalar style.
+  ///
+  /// See http://yaml.org/spec/1.2/spec.html#style/flow/single-quoted.
+  static const SINGLE_QUOTED = const ScalarStyle._("SINGLE_QUOTED");
+
+  /// The double-quoted scalar style.
+  ///
+  /// See http://yaml.org/spec/1.2/spec.html#style/flow/double-quoted.
+  static const DOUBLE_QUOTED = const ScalarStyle._("DOUBLE_QUOTED");
+
+  final String name;
+
+  /// Whether this is a quoted style ([SINGLE_QUOTED] or [DOUBLE_QUOTED]).
+  bool get isQuoted => this == SINGLE_QUOTED || this == DOUBLE_QUOTED;
+
+  const ScalarStyle._(this.name);
+
+  String toString() => name;
+}
+
+/// An enum of collection styles.
+class CollectionStyle {
+  /// No source style was specified.
+  ///
+  /// This usually indicates a collection constructed with [YamlList.wrap] or
+  /// [YamlMap.wrap].
+  static const ANY = const CollectionStyle._("ANY");
+
+  /// The indentation-based block style.
+  ///
+  /// See http://yaml.org/spec/1.2/spec.html#id2797293.
+  static const BLOCK = const CollectionStyle._("BLOCK");
+
+  /// The delimiter-based block style.
+  ///
+  /// See http://yaml.org/spec/1.2/spec.html#id2790088.
+  static const FLOW = const CollectionStyle._("FLOW");
+
+  final String name;
+
+  const CollectionStyle._(this.name);
+
+  String toString() => name;
+}