anchor.diff:          { model' with messages = (x,y,message)::model.messages }, []
       | _ ->
         model, []
  +  | Reveal ->
  +    match model.maze with
  +    | Some(maze) ->
  +       let xdim, ydim = Maze.dimensions maze
  +       let revealed = [for x in 0..xdim do for y in 0..ydim do yield (x,y)]
  +       { model with revealed = Set.ofList revealed }, []
  +    | None -> model, []
   
   module Key =
     let left = KeyDetect 37
  
positive.code:         ]
        R.div [] [
          R.button [OnClick (fun _ -> dispatch Refresh)] [R.str "New Maze"]
          ]
        R.div [] [
          R.text [] [
  
negative.code: 
  type Msg =
    | Refresh
    | Reveal
    | Move of Direction
  
  let init _ =
  