anchor.diff:                          let model = FieldModel.updateFieldTransitionOpt (constant None) model
                           let model =
                               FieldModel.updateAvatar (fun avatar ->
  +                                let avatar = AvatarModel.updateDirection (constant fieldTransition.FieldDirection) avatar
                                   let avatar = AvatarModel.updateDirection (constant fieldTransition.FieldDirection) avatar
                                   let avatar = AvatarModel.updateIntersectedBodyShapes (constant []) avatar
                                   avatar)
  
positive.code:                 just world
  
              | MoveAvatar position ->
                  let physicsId = Simulants.FieldAvatar.GetPhysicsId world
                  let world = World.setBodyPosition position physicsId world
                  just world
  
              | PlaySound (delay, volume, sound) ->
  
negative.code: 
                  [// tile map
                   Content.tileMap Simulants.FieldTileMap.Name
                      [Entity.Depth == Constants.Field.BackgroundDepth
                       Entity.TileMapAsset <== model --> fun model ->
                          match Map.tryFind model.FieldType data.Value.Fields with
                          | Some fieldData -> fieldData.FieldTileMap
  