RunOnceResult[S; T] = object
  step: S
  item: Optional[T]

func runOnceResult[S; T](step: S; item: Optional[T]): RunOnceResult[S, T]

func step[SA; T](X: typedesc[RunOnceResult[SA, T]]; SB: typedesc): PLens[X, SA, SB,
    RunOnceResult[SB, T]]

func step[S; T](X: typedesc[RunOnceResult[S, T]]): Lens[X, S]

func item[S; A](X: typedesc[RunOnceResult[S, A]]; B: typedesc): PLens[X, Optional[A],
    Optional[B], RunOnceResult[S, B]]

func item[S; T](X: typedesc[RunOnceResult[S, T]]): Lens[X, Optional[T]]