Representing HTML as first-class entities in Dart

gistfile1.dart

// This is a really bad implementation of a simple algebraic data type in Dart please don't kill meee~
class None implements Option<None> {
  map(f)          => this;
  operator >= (f) => this;
  operator |  (x) => x;
  None();
}

class Option<T> {
  final        value;
  static final _none = new None();

  Option<T> map(T f(T))                  => new Option(f(value));
  Option<T> operator >= (Option<T> f(T)) => f(value);
  Option<T> operator |  (Option<T> x)    => this; 

  Option(this.value);
  factory Option.none() => _none;
}



abstract class Html<A> {
  String toString();
  Option<A> parent;
}

class Element<A, B> extends Html<B> {
  final String tag;
  List<A> children;

  toString() => "<$tag>${children.map((c) => c.toString()).join('')}</$tag>";
}

// You'd need to use a different approach to encode the hierarchy here because
// as far as I know, Dart doesn't support union types.
class Text extends Html<Element> {
  final String text;
  Option<Element> parent = new Option.none();

  toString() => text;

  Text(this.text);
}

class ListItem extends Element<Text, Element> {
  final tag = "li";
  ListItem(String x) => this.children = [x];
}

class List extends Element<ListItem, Element> {
  final tag = "ul";
  List<ListItem> children;
  List(this.children);
}


// Using
class TodoList {
  final List<String> items;
  toString() => new List(items.map((a) => new ListItem(new Text(a)))).toString();
  TodoList(this.items);
}

main() {
  var x = new TodoList([ "First thing", "Second thing", "Third thing" ]);
  print(x.toString());
}