VirtualDOM.fs

div [] 
  [for i in 0 .. model.Length-1 ->
    div 
      [] 
      [ for j in 0 .. model.Length-1 ->
          input
              [ maxlength 1
                property "value" 
                    (match model.[i].[j] with
                     | 0 -> unbox ""
                     | v -> unbox (v.ToString()))
                onInput (fun x -> ChangeBox ((i,j), int (unbox x)))
              ]
      ]
  ]