anchor.diff:                          let tree = renderTree state.AppState.View post state.AppState.Model
                           let rootNode = renderer.CreateElement tree
                           startElem.appendChild(rootNode) |> ignore
  +                        state.Init post
                           return! loop {state with CurrentTree = Some tree; Node = Some rootNode}
                       | Some rootNode, Some currentTree ->
                           let! message = inbox.Receive()
  
positive.code:     type App<'TModel, 'TMessage> =
          {
              AppState: AppState<'TModel, 'TMessage>
              JsCalls: (unit -> unit) list
              Node: Node option
              CurrentTree: obj option
  
negative.code:     let createApp appState =
          {
              AppState = appState
              Init = (fun _ -> ())
              JsCalls = []
              Node = None
              CurrentTree = None
  