Rewrite the pkg/yaml parser.

pkg/yaml/lib/src/event.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.event;
+
+import 'package:source_span/source_span.dart';
+
+import 'style.dart';
+import 'yaml_document.dart';
+
+/// An event emitted by a [Parser].
+class Event {
+  /// The event type.
+  final EventType type;
+
+  /// The span associated with the event.
+  final FileSpan span;
+
+  Event(this.type, this.span);
+
+  String toString() => type.toString();
+}
+
+/// An event indicating the beginning of a YAML document.
+class DocumentStartEvent implements Event {
+  get type => EventType.DOCUMENT_START;
+  final FileSpan span;
+
+  /// The document's `%YAML` directive, or `null` if there was none.
+  final VersionDirective versionDirective;
+
+  /// The document's `%TAG` directives, if any.
+  final List<TagDirective> tagDirectives;
+
+  /// Whether the document started implicitly (that is, without an explicit
+  /// `===` sequence).
+  final bool isImplicit;
+
+  DocumentStartEvent(this.span, {this.versionDirective,
+          List<TagDirective> tagDirectives, this.isImplicit: true})
+      : tagDirectives = tagDirectives == null ? [] : tagDirectives;
+
+  String toString() => "DOCUMENT_START";
+}
+
+/// An event indicating the end of a YAML document.
+class DocumentEndEvent implements Event {
+  get type => EventType.DOCUMENT_END;
+  final FileSpan span;
+
+  /// Whether the document ended implicitly (that is, without an explicit
+  /// `...` sequence).
+  final bool isImplicit;
+
+  DocumentEndEvent(this.span, {this.isImplicit: true});
+
+  String toString() => "DOCUMENT_END";
+}
+
+/// An event indicating that an alias was referenced.
+class AliasEvent implements Event {
+  get type => EventType.ALIAS;
+  final FileSpan span;
+
+  /// The name of the anchor.
+  final String name;
+
+  AliasEvent(this.span, this.name);
+
+  String toString() => "ALIAS $name";
+}
+
+/// A base class for events that can have anchor and tag properties associated
+/// with them.
+abstract class _ValueEvent implements Event {
+  /// The name of the value's anchor, or `null` if it wasn't anchored.
+  String get anchor;
+
+  /// The text of the value's tag, or `null` if it wasn't tagged.
+  String get tag;
+
+  String toString() {
+    var buffer = new StringBuffer('$type');
+    if (anchor != null) buffer.write(" &$anchor");
+    if (tag != null) buffer.write(" $tag");
+    return buffer.toString();
+  }
+}
+
+/// An event indicating a single scalar value.
+class ScalarEvent extends _ValueEvent {
+  get type => EventType.SCALAR;
+  final FileSpan span;
+  final String anchor;
+  final String tag;
+
+  /// The contents of the scalar.
+  final String value;
+
+  /// The style of the scalar in the original source.
+  final ScalarStyle style;
+
+  ScalarEvent(this.span, this.value, this.style, {this.anchor, this.tag});
+
+  String toString() => "${super.toString()} \"$value\"";
+}
+
+/// An event indicating the beginning of a sequence.
+class SequenceStartEvent extends _ValueEvent {
+  get type => EventType.SEQUENCE_START;
+  final FileSpan span;
+  final String anchor;
+  final String tag;
+
+  /// The style of the collection in the original source.
+  final CollectionStyle style;
+
+  SequenceStartEvent(this.span, this.style, {this.anchor, this.tag});
+}
+
+/// An event indicating the beginning of a mapping.
+class MappingStartEvent extends _ValueEvent {
+  get type => EventType.MAPPING_START;
+  final FileSpan span;
+  final String anchor;
+  final String tag;
+
+  /// The style of the collection in the original source.
+  final CollectionStyle style;
+
+  MappingStartEvent(this.span, this.style, {this.anchor, this.tag});
+}
+
+/// An enum of types of [Event] object.
+class EventType {
+  static const STREAM_START = const EventType._("STREAM_START");
+  static const STREAM_END = const EventType._("STREAM_END");
+
+  static const DOCUMENT_START = const EventType._("DOCUMENT_START");
+  static const DOCUMENT_END = const EventType._("DOCUMENT_END");
+
+  static const ALIAS = const EventType._("ALIAS");
+  static const SCALAR = const EventType._("SCALAR");
+
+  static const SEQUENCE_START = const EventType._("SEQUENCE_START");
+  static const SEQUENCE_END = const EventType._("SEQUENCE_END");
+
+  static const MAPPING_START = const EventType._("MAPPING_START");
+  static const MAPPING_END = const EventType._("MAPPING_END");
+
+  final String name;
+
+  const EventType._(this.name);
+
+  String toString() => name;
+}