(* This file was originally part of lwt-dllist, which is licensed
   under MIT: https://github.com/ocsigen/lwt/blob/master/LICENSE.md. *)

type 'a t
  (** Type of a sequence holding values of type ['a] *)

type 'a node
  (** Type of a node holding one value of type ['a] in a sequence *)

(** {2 Operation on nodes} *)

val remove : 'a node -> unit
  (** Removes a node from the sequence it is part of. It does nothing
      if the node has already been removed. *)

(** {2 Operations on sequence} *)

val create : unit -> 'a t
  (** [create ()] creates a new empty sequence *)

val is_empty : 'a t -> bool
  (** Returns [true] iff the given sequence is empty *)

val add_l : 'a -> 'a t -> 'a node
  (** [add_l x s] adds [x] to the left of the sequence [s] *)

val add_r : 'a -> 'a t -> 'a node
  (** [add_r x s] adds [x] to the right of the sequence [s] *)

val take_l : 'a t -> 'a
  (** [take_l x s] removes and returns the leftmost element of [s]

      @raise Not_found if the sequence is empty *)

val take_r : 'a t -> 'a
  (** [take_l x s] removes and returns the rightmost element of [s]

      @raise Not_found if the sequence is empty *)

(** {2 Sequence iterators} *)

(** Note: it is OK to remove a node while traversing a sequence *)

(* val fold_l : ('a -> 'b -> 'b) -> 'a t -> 'b -> 'b *)
(*   (\** [fold_l f s] is: *)
(*       {[ *)
(*         fold_l f s x = f en (... (f e2 (f e1 x))) *)
(*       ]} *)
(*       where [e1], [e2], ..., [en] are the elements of [s] *)
(*   *\) *)

val fold_r : ('a -> 'b -> 'b) -> 'a t -> 'b -> 'b
  (** [fold_r f s] is:
      {[
        fold_r f s x = f e1 (f e2 (... (f en x)))
      ]}
      where [e1], [e2], ..., [en] are the elements of [s]
  *)

val find : ('a -> bool) -> 'a t -> 'a
  (** [find_node_l f s] returns the first element of [s] starting from the left
      that satisfies [f] or raises [Not_found] if none exists. *)

val exists : ('a -> bool) -> 'a t -> bool
  (** [find_node_l f s] returns [true] if some node [s] starting from the left
      that satisfies [f] or returns [false] if none exists. *)