(*
copyright (c) 2013, simon cruanes
all rights reserved.

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(** {1 Bidirectional Iterators}

Iterators that can be traversed in both directions *)

type 'a t =
  | Nil
  | Cons of (unit -> 'a t) * 'a * (unit -> 'a t)

val nil : 'a t
  (** Empty iterator *)

val insert_before : 'a -> 'a t -> 'a t
  (** Insert the given element before the current slot in the
   *  given iterator *)

val insert_after : 'a -> 'a t -> 'a t
  (** Insert the element right after the current one *)

val left : 'a t -> 'a t
  (** Go left once. Doesn't do anything on empty iterator. *)

val right : 'a t -> 'a t
  (** Go right once. Doesn't do anything on empty iterator. *)

val graft_before : inner:'a t -> 'a t -> 'a t
  (** [insert ~inner outer] grafts [inner] just before the current element of
      [outer]. *)

val graft_after : inner:'a t -> 'a t -> 'a t

val rev : 'a t -> 'a t
  (** Reverse the order of iteration *)

(** {2 Right-iteration}
traverse the right part of the iterator. traversing the left is
easily done with {!rev}. *)

val fold : ('a -> 'b -> 'a) -> 'a -> 'b t -> 'a
  (** Fold on elements starting from the current one, to the right end *)

val to_rev_list : 'a t -> 'a list
  (** To reverse list *)

val to_list : 'a t -> 'a list
  (** Conversion to list. Only traverse the right part. *)

val of_list : 'a list -> 'a t
  (** Iterate on the list *)

(** {2 Full constructor} *)

val of_lists : 'a list -> 'a -> 'a list -> 'a t

(** {2 Moves} *)

val left_n : int -> 'a t -> 'a list * 'a t
  (** Move left n times, and return the n elements traversed (at most),
     from left-most one to right_most one.*)

val right_n : int -> 'a t -> 'a list * 'a t