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

lib/yaml/yaml_map.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.
+
+/**
+ * This class wraps behaves almost identically to the normal Dart Map

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

"wraps behaves"?

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

Fixed.

+ * implementation, with the following differences:
+ *
+ * * It allows null, NaN, boolean, list, and map keys.
+ * * It is itself Hashable.
+ * * It defines `==` structurally. That is, `yamlMap1 == yamlMap2` if they have
+ *   the same contents.
+ */
+class YamlMap implements Map, Hashable {
+  Map _map;
+
+  YamlMap() : _map = new Map();
+
+  YamlMap.from(Map map) : _map = new Map.from(map);
+
+  bool containsValue(value) => _map.containsValue(value);
+  bool containsKey(key) => _map.containsKey(_wrapKey(key));
+  operator [](key) => _map[_wrapKey(key)];
+  operator []=(key, value) { _map[_wrapKey(key)] = value; }
+  putIfAbsent(key, ifAbsent()) => _map.putIfAbsent(_wrapKey(key), ifAbsent);
+  remove(key) => _map.remove(_wrapKey(key));
+  void clear() => _map.clear();
+  void forEach(void f(key, value)) =>
+    _map.forEach((k, v) => f(_unwrapKey(k), v));
+  Collection getKeys() => _map.getKeys().map(_unwrapKey);
+  Collection getValues() => _map.getValues();
+  int get length() => _map.length;
+  bool isEmpty() => _map.isEmpty();
+  String toString() => _map.toString();
+
+  int hashCode() => _hashCode(_map);
+
+  bool operator ==(other) {
+    if (other is! YamlMap) return false;
+    return _mapEquals(this, other);
+  }
+
+  /** Wraps an object for use as a key in the map. */
+  _wrapKey(obj) {
+    if (obj != null && obj is! bool && obj is! List &&
+        (obj is! double || !obj.isNan()) &&
+        (obj is! Map || obj is YamlMap)) {
+      return obj;
+    }
+    return new _WrappedHashKey._(obj);
+  }
+
+  /** Unwraps an object that was used as a key in the map. */
+  _unwrapKey(obj) => obj is _WrappedHashKey ? obj.value : obj;
+}
+
+/**
+ * A class for wrapping normally-unhashable objects that are being used as keys
+ * in a YamlMap.
+ */
+class _WrappedHashKey implements Hashable {
+  var value;
+
+  _WrappedHashKey._(this.value);
+
+  int hashCode() => _hashCode(value);
+
+  String toString() => value.toString();
+
+  /** This is defined as both values being structurally equal. */
+  bool operator ==(other) {
+    if (other is! _WrappedHashKey) return false;
+    _WrappedHashKey otherWrappedKey = other;
+    return _deepEquals(this.value, other.value);
+  }
+}
+
+/**
+ * Returns the hash code for [obj]. This includes null, true, false, maps, and
+ * lists.
+ */
+int _hashCode(obj) {

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

This will do Bad Things with cyclic structures. Does that matter? Should at the
least document this fact. (Ditto functions below.)

This is a topic close to Josh's heart, so you could ask him about it if you want
some ideas on how this should behave.

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

I've fixed hashCode and deepEquals to work properly with cyclic structures. It's
not particularly efficient, since Dart doesn't have any notion of per-object
ids, but I doubt anyone will be using map keys that are deeply-nested enough
that it'll matter.

+  if (obj == null) return 0;
+  if (obj == true) return 1;
+  if (obj == false) return 2;
+  if (obj is Map) return _hashCode(obj.getKeys()) ^ _hashCode(obj.getValues());
+  if (obj is List) {
+    // This is probably a really bad hash function, but presumably we'll get this
+    // in the standard library before it actually matters.
+    int hash = 0;
+    for (var e in obj) {
+      hash ^= _hashCode(e);
+    }
+    return hash;
+  }
+  return obj.hashCode();
+}
+
+/** Returns whether [list1] and [list2] are structurally equal. */
+bool _listEquals(List list1, List list2) {
+  if (list1.length != list2.length) return false;
+
+  for (var i = 0; i < list1.length; i++) {
+    if (!_deepEquals(list1[i], list2[i])) return false;
+  }
+
+  return true;
+}
+
+/** Returns whether [map1] and [map2] are structurally equal. */
+bool _mapEquals(Map map1, Map map2) {
+  if (map1.length != map2.length) return false;
+
+  for (var key in map1.getKeys()) {
+    if (!map2.containsKey(key)) return false;
+    if (!_deepEquals(map1[key], map2[key])) return false;
+  }
+
+  return true;
+}
+
+/**
+ * Returns whether two doubles are equivalent. This differs from `d1 == d2` in
+ * that it considers NaN to be equal to itself.
+ */
+bool _doubleEquals(double d1, double d2) {
+  if (d1.isNaN() && d2.isNaN()) return true;
+  return d1 == d2;
+}
+
+/** Returns whether two objects are structurally equivalent. */
+bool _deepEquals(obj1, obj2) {
+  if (obj1 is List && obj2 is List) return _listEquals(obj1, obj2);
+  if (obj1 is Map && obj2 is Map) return _mapEquals(obj1, obj2);
+  if (obj1 is double && obj2 is double) return _doubleEquals(obj1, obj2);
+  return obj1 == obj2;
+}