anchor.diff:  open Nu
   
   [<AutoOpen>]
  -module ModelViewMessageEffect =
  -
  -    /// Pair a None value with a model.
  -    let inline just model = (model, None)
  +module ModelViewMessageCommand =
  +
  +    /// Pair an empty list of commands with a model.
  +    let inline just model = (model, [])
   
       /// Specifies the view phase of Nu's MVME form factor.
       type Phase =
  
positive.code:             let model = property.Get world
              this.View (Actualize, model, layer, world)
  
          abstract member Binding : 'model * Layer * World -> Binding<'message, 'effect, Layer, World> list
          abstract member Message : 'message * 'model * Layer * World -> 'model * 'effect option
          abstract member Effect : 'effect * 'model * Layer * World -> World
          abstract member View : Phase * 'model * Layer * World -> World
  
  [<AutoOpen>]
  module ScreenDispatcherModule =
  
      type [<AbstractClass>] ScreenDispatcher<'model, 'message, 'effect>
          (propertyFn : Screen -> PropertyTag<'model, World>) =
          inherit ScreenDispatcher ()
  
  
negative.code:                             let messageOpt = binding.MakeValueOpt evt
                              match messageOpt with
                              | Some message ->
                                  let (model, commands) = this.Message (message, model, screen, world)
                                  let world = property.Set model world
                                  List.fold (fun world command ->
                                      let model = property.Get world
                                      this.Command (command, model, screen, world))
                                      world commands
                              | None -> world)
                              screen binding.Stream world
                      | Effect binding ->
  