lazyy.ml

  (* find the root inputs of [x] *)
  let find_roots x =
    let s = Owl_utils.Stack.make () in
    let rec _find x =
      Array.iter (fun n ->
        if n.op = Noop then Owl_utils.Stack.push s n
        else _find n
      ) x.prev
    in
    _find x;
    Owl_utils.Stack.to_array s

  (* update [x]'s dependency graph by invalidating stale nodes *)
  let update_graph x =
    let rec _update x =
      let valid = ref (is_valid x) in
      Array.iter (fun n ->
        valid := !valid || _update n
      ) x.prev;
      if !valid = false then invalidate x;
      !valid
    in
    _update x |> ignore