Rewrite the pkg/yaml parser.

pkg/yaml/lib/src/composer.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.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 {
-  /// The root node of the serialization tree.
-  final Node _root;
-
-  /// Map from anchor names to the most recent representation graph node with
-  /// that anchor.
-  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.
-  var _idCounter = 0;
-
-  Composer(this._root);
-
-  /// Runs the Composer to produce a representation graph.
-  Node compose() => _root.visit(this);
-
-  /// Returns the anchor to which an alias node refers.
-  Node visitAlias(AliasNode alias) {
-    if (!_anchors.containsKey(alias.anchor)) {
-      throw new YamlException("No anchor for alias ${alias.anchor}.",
-          alias.span);
-    }
-    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) {
-    if (scalar.tag.name == "!") {
-      return setAnchor(scalar, parseString(scalar));
-    } else if (scalar.tag.name == "?") {
-      for (var fn in [parseNull, parseBool, parseInt, parseFloat]) {
-        var result = fn(scalar);
-        if (result != null) return result;
-      }
-      return setAnchor(scalar, parseString(scalar));
-    }
-
-    var result = _parseByTag(scalar);
-    if (result != null) return setAnchor(scalar, result);
-    throw new YamlException('Invalid literal for ${scalar.tag}.',
-        scalar.span);
-  }
-
-  ScalarNode _parseByTag(ScalarNode scalar) {
-    switch (scalar.tag.name) {
-      case "null": return parseNull(scalar);
-      case "bool": return parseBool(scalar);
-      case "int": return parseInt(scalar);
-      case "float": return parseFloat(scalar);
-      case "str": return parseString(scalar);
-    }
-    throw new YamlException('Undefined tag: ${scalar.tag}.', scalar.span);
-  }
-
-  /// Assigns a tag to the sequence and recursively composes its contents.
-  Node visitSequence(SequenceNode seq) {
-    var tagName = seq.tag.name;
-    if (tagName != "!" && tagName != "?" && tagName != Tag.yaml("seq")) {
-      throw new YamlException("Invalid tag for sequence: ${seq.tag}.",
-          seq.span);
-    }
-
-    var result = setAnchor(seq,
-        new SequenceNode(Tag.yaml('seq'), null, seq.span));
-    result.content = super.visitSequence(seq);
-    return result;
-  }
-
-  /// Assigns a tag to the mapping and recursively composes its contents.
-  Node visitMapping(MappingNode map) {
-    var tagName = map.tag.name;
-    if (tagName != "!" && tagName != "?" && tagName != Tag.yaml("map")) {
-      throw new YamlException("Invalid tag for mapping: ${map.tag}.",
-          map.span);
-    }
-
-    var result = setAnchor(map,
-        new MappingNode(Tag.yaml('map'), null, map.span));
-    result.content = super.visitMapping(map);
-    return result;
-  }
-
-  /// If the serialization tree node [anchored] has an anchor, records that
-  /// that anchor is pointing to the representation graph node [result].
-  Node setAnchor(Node anchored, Node result) {
-    if (anchored.anchor == null) return result;
-    result.anchor = '${_idCounter++}';
-    _anchors[anchored.anchor] = result;
-    return result;
-  }
-
-  /// Parses a null scalar.
-  ScalarNode parseNull(ScalarNode scalar) {
-    if (new RegExp(r"^(null|Null|NULL|~|)$").hasMatch(scalar.content)) {
-      return new ScalarNode(Tag.yaml("null"), scalar.span, value: null);
-    } else {
-      return null;
-    }
-  }
-
-  /// Parses a boolean scalar.
-  ScalarNode parseBool(ScalarNode scalar) {
-    var match = new RegExp(r"^(?:(true|True|TRUE)|(false|False|FALSE))$").
-        firstMatch(scalar.content);
-    if (match == null) return null;
-    return new ScalarNode(Tag.yaml("bool"), scalar.span,
-        value: match.group(1) != null);
-  }
-
-  /// Parses an integer scalar.
-  ScalarNode parseInt(ScalarNode scalar) {
-    var match = new RegExp(r"^[-+]?[0-9]+$").firstMatch(scalar.content);
-    if (match != null) {
-      return new ScalarNode(Tag.yaml("int"), scalar.span,
-          value: int.parse(match.group(0)));
-    }
-
-    match = new RegExp(r"^0o([0-7]+)$").firstMatch(scalar.content);
-    if (match != null) {
-      int n = int.parse(match.group(1), radix: 8);
-      return new ScalarNode(Tag.yaml("int"), scalar.span, value: n);
-    }
-
-    match = new RegExp(r"^0x[0-9a-fA-F]+$").firstMatch(scalar.content);
-    if (match != null) {
-      return new ScalarNode(Tag.yaml("int"), scalar.span,
-          value: int.parse(match.group(0)));
-    }
-
-    return null;
-  }
-
-  /// Parses a floating-point scalar.
-  ScalarNode parseFloat(ScalarNode scalar) {
-    var match = new RegExp(
-          r"^[-+]?(\.[0-9]+|[0-9]+(\.[0-9]*)?)([eE][-+]?[0-9]+)?$").
-        firstMatch(scalar.content);
-    if (match != null) {
-      // 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"\.$"), "");
-      return new ScalarNode(Tag.yaml("float"), scalar.span,
-          value: double.parse(matchStr));
-    }
-
-    match = new RegExp(r"^([+-]?)\.(inf|Inf|INF)$").firstMatch(scalar.content);
-    if (match != null) {
-      var value = match.group(1) == "-" ? -double.INFINITY : double.INFINITY;
-      return new ScalarNode(Tag.yaml("float"), scalar.span, value: value);
-    }
-
-    match = new RegExp(r"^\.(nan|NaN|NAN)$").firstMatch(scalar.content);
-    if (match != null) {
-      return new ScalarNode(Tag.yaml("float"), scalar.span, value: double.NAN);
-    }
-
-    return null;
-  }
-
-  /// Parses a string scalar.
-  ScalarNode parseString(ScalarNode scalar) =>
-    new ScalarNode(Tag.yaml("str"), scalar.span, value: scalar.content);
-}