Implementation of HtmlWriter for the HTML DSL using using.

Using.Html.cs

class Program
{
  static void Main(string[] args)
  {
    new HtmlWriter(Console.Out).Write();
  }
}

class HtmlWriter : BaseHtmlWriter
{
  public HtmlWriter(TextWriter tw) : base(tw) {}

  public override void Write()
  {
    using(Html())
    {
      using (Head())
      {
        using (Title())
        {
          Text("Greeting");
        }
      }
      using (Body(Bgcolor("pink")))
      {
        using(P(Style("font-size:large")))
        {
          Text("Hello world!");
        }
      }
    }
  }
}

class DisposableWriter : IDisposable
{
  private readonly Stack<string> _tags = new Stack<string>();
  private readonly TextWriter _;
            
  public DisposableWriter(TextWriter tw)
  {
    _ = tw;
  }

  public IDisposable Tag(string tag, params string[] attrs)
  {
    string s = attrs.Length > 0 ? tag + " " + string.Join(" ", attrs) : tag;
    Write("<" + s + ">");
    _tags.Push(tag);
    return this;
  }

  public void Text(string s)
  {
    Write(s);
  }

  private void Write(string s) {
    _.WriteLine();
  }

  public void Dispose()
  {
    var tag = _tags.Pop();
    Write("</" + tag + ">");
  }
}

abstract class BaseHtmlWriter
{      
  private readonly DisposableWriter _;

  protected BaseHtmlWriter(TextWriter tw)
  {
    _ = new DisposableWriter(tw);
  }

  protected IDisposable Html()
  {
    return _.Tag("html");
  }

  protected IDisposable Body(params string[] attrs)
  {
    return _.Tag("body", attrs);
  }

  // More tags...

  protected string Bgcolor(string value)
  {
    return Attr("bgcolor", value);
  }

  protected string Style(string value)
  {
    return Attr("style", value);
  }

  // More attributes...

  protected string Attr(string key, string value)
  {
    return key + "=\"" + value + "\"";
  }

  protected void Text(string s)
  {
    _.Text(s);
  }

  public abstract void Write();
}