Source file sigs.ml

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(** A mutable structure that holds at most a fixed number of values of a same
    type. Values are never removed, once the limit is reached, adding a value
    replaces the oldest-promoted one in the buffer.

    The function [promote] (see below) allows to pull a node to the front of
    the buffer. *)
module type COLLECTION_BARE = sig

  (** The type of bounded-size buffers. *)
  type 'a t

  (** [node]s are boxes that contain data. Boxes are never meant to be returned
      to the end user (they can be unsafe), they are meant to build some
      abstraction on top of the buffer.

      In order to make the module safe and remove all notion of box, use the
      functor [Misc.Unbox]. *)
  type 'a node

  (** [data n] is the value contained in the node [n]. *)
  val data : 'a node -> 'a

  (** [create n] allocates a buffer that can hold up to [n] elements.
      @raise [Invalid_argument] if [n] is 0 or less. *)
  val create : int -> 'a t

  (** [capacity b] is the number of elements that [b] can hold. *)
  val capacity : 'a t -> int

  (** [length b] is the number of elements that are currently in [b]. *)
  val length : 'a t -> int

  (** [add b v] adds the value [v] to the buffer [b]. If the buffer [b] already
      has [capacity b] values, then a value is dropped.

      [adds b v] returns the node containing the value [v]. This node can be
      used to [promote] or [remove] the value [v] from the buffer [b]. *)
  val add : 'a t -> 'a -> 'a node

  (** [add_and_return_erased b v] has the same effect as [add b v] but it
      returns the dropped value when applicable (and [None] otherwise). *)
  val add_and_return_erased : 'a t -> 'a -> ('a node * 'a option)

  (** [add_list b vs] adds each element of the list [vs] in the order they
      appear in the list. It returns a list of nodes, for each of the inserted
      elements.

      If [length vs > capacity b], then each value from [vs] is added, but the
      ones at the front of the list are popped. In this case, [add_list b vs]
      returns a list of [capacity b] nodes only. *)
  val add_list : 'a t -> 'a list -> 'a node list

  (** [clear b] removes all values from the buffer [b]. *)
  val clear : 'a t -> unit

  (** [fold b ~init ~f] folds over the value of the buffer [b], newest to oldest. *)
  val fold : 'a t -> init:'b -> f:('b -> 'a node -> 'b) -> 'b

  (** [fold_oldest_first b ~init ~f] folds over the value of the buffer [b], oldest to newest. *)
  val fold_oldest_first : 'a t -> init:'b -> f:('b -> 'a node -> 'b) -> 'b

  (** [elements b] is a list of nodes from [b]. They appear oldest first, newest
      last. *)
  val elements : 'a t -> 'a node list

  val elements_data : 'a t -> 'a list

  (** [remove b n] removes the node [n] from the buffer [b].

      The behavior of this function is undefined if [n] is not part of [b],
      i.e., if [List.exists ((==) n) (elements b)] is [false].

      It is the responsibility of the user of this library (presumably, another
      library wrapping the primitives of this one) to ensure this is never the
      case. *)
  val remove : 'a t -> 'a node -> unit

  (** [promote b n] places the node [n] to the front of the buffer [b], making
      the node [n] the newest of the nodes of the buffer [b].

      [promote b n] is similar to [remove b n; ignore (add b @@ data n)] except
      that: it is more efficient, and it keeps the value [data n] in the same
      node it was originally inserted in.

      The behavior of this function is undefined if [n] is not part of [b],
      i.e., if [List.exists ((==) n) (elements b)] is [false]. *)
  val promote : 'a t -> 'a node -> unit

end

module type COLLECTION = sig

  include COLLECTION_BARE

  val promote_read : 'a t -> 'a node -> unit

  val promote_write : 'a t -> 'a node -> unit

end


(** A mutable structure that holds at most a fixed number of values of a same
    type. Values are not removed by hand, instead, once the limit is reached,
    adding a value replaces the oldest one in the buffer. *)
module type UNBOXED_COLLECTION = sig

  (** The type of bounded-size buffers. *)
  type 'a t

  (** [create n] allocates a ring buffer that can hold up to [n] values.
      @raise [Invalid_argument] if [n] is 0 or less. *)
  val create : int -> 'a t

  (** [capacity b] is the number of elements that [b] can hold. *)
  val capacity : 'a t -> int

  (** [length b] is the number of elements that are currently in [b]. *)
  val length : 'a t -> int

  (** [add b v] adds the value [v] to the buffer [b]. If the buffer [b] already
      has [capacity b] values, the oldest of its values is dropped. *)
  val add : 'a t -> 'a -> unit

  (** [add_and_return_erased b v] has the same effect as [add b v] but it
      returns the dropped value when applicable. *)
  val add_and_return_erased : 'a t -> 'a -> 'a option

  (** [add_list b vs] adds each element of the list [vs] in the order they
      appear in the list. Note that if [List.length vs > capacity b], then only
      the last [capacity b] elements of the list remain in [b] at the end. *)
  val add_list : 'a t -> 'a list -> unit

  (** [clear b] removes all values from the buffer [b]. *)
  val clear : 'a t -> unit

  (** [fold b ~init ~f] folds over the value of the buffer [b], newest to oldest. *)
  val fold : 'a t -> init:'b -> f:('b -> 'a -> 'b) -> 'b

  (** [fold_oldest_first b ~init ~f] folds over the value of the buffer [b],
      oldest to newest. *)
  val fold_oldest_first : 'a t -> init:'b -> f:('b -> 'a -> 'b) -> 'b

  (** [elements b] is a list that contains the same elements as the buffer [b],
      oldest first, newest last. *)
  val elements : 'a t -> 'a list

end