let draw =
  () {
    case Dom.Canvas.fromDomElement(canvas) {
      Maybe::Just(el) =>
        {
          el
          |> Canvas.beginPath
          |> Canvas.arc(150, 75, 50, 0, 2 * `Math.PI`)
          |> Canvas.stroke
          ""
        }
      Maybe::Nothing =>
        ""
    }
  }
{
  await Timer.timeout(0)
  draw()
}
<canvas as canvas/>