(*
Copyright (c) 2013, Simon Cruanes
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*)

(** {1 Persistent hash-table on top of OCaml's hashtables} *)

type 'a sequence = ('a -> unit) -> unit

module type HashedType = sig
  type t
  val equal : t -> t -> bool
  val hash : t -> int
end

(** {2 Signature of such a hashtable} *)

module type S = sig
  type key
  type 'a t

  val empty : unit -> 'a t
    (** Empty table. The table will be allocated at the first binding *)

  val create : int -> 'a t
    (** Create a new hashtable *)

  val is_empty : 'a t -> bool
    (** Is the table empty? *)

  val find : 'a t -> key -> 'a
    (** Find the value for this key, or raise Not_found *)

  val mem : 'a t -> key -> bool
    (** Is the key bound? *)

  val length : 'a t -> int
    (** Number of bindings *)

  val replace : 'a t -> key -> 'a -> 'a t
    (** Add the binding to the table, returning a new table. This erases
        the current binding for [key], if any. *)

  val remove : 'a t -> key -> 'a t
    (** Remove the key *)

  val copy : 'a t -> 'a t
    (** Fresh copy of the table; the underlying structure is not shared
        anymore, so using both tables alternatively will be efficient *)

  val merge : (key -> 'a option -> 'a option -> 'a option) -> 'a t -> 'a t -> 'a t
    (** Merge two tables together into a new table *)

  val iter : 'a t -> (key -> 'a -> unit) -> unit
    (** Iterate over bindings *)

  val fold : ('b -> key -> 'a -> 'b) -> 'b -> 'a t -> 'b
    (** Fold over bindings *)

  val of_seq : ?init:'a t -> (key * 'a) sequence -> 'a t
    (** Add (replace) bindings from the sequence to the table *)

  val of_list : ?init:'a t -> (key * 'a) list -> 'a t

  val to_seq : 'a t -> (key * 'a) sequence
    (** Sequence of the bindings of the table *)

  val to_list : 'a t -> (key * 'a) list
end

(** {2 Implementation} *)

module Make(H : HashedType) : S with type key = H.t