(*
Copyright (c) 2013, Simon Cruanes
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(** {1 Functional (persistent) hashtable} *)

(** {2 Signatures} *)

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

(** The signature for such a functional hashtable *)
module type S = sig
  type 'a t
  type key

  val empty : int -> 'a t
    (** The empty hashtable (with sub-hashtables of given size) *)

  val is_empty : _ t -> bool

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

  val mem : 'a t -> key -> bool
    (** Check whether the key is bound in this hashtable *)

  val replace : 'a t -> key -> 'a -> 'a t
    (** [replace t key val] returns a copy of [t] where [key] binds to [val] *)

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

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

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

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

  val to_seq : 'a t -> (key * 'a) Sequence.t

  val of_seq : ?size:int -> (key * 'a) Sequence.t -> 'a t
end

(** {2 Persistent array} *)

module PArray : sig
  type 'a t

  val make : int -> 'a -> 'a t

  val get : 'a t -> int -> 'a

  val set : 'a t -> int -> 'a -> 'a t

  val fold_left : ('b -> 'a -> 'b) -> 'b -> 'a t -> 'b

  val length : 'a t -> int
end

(** {2 Tree-like hashtable} *)

module Tree(X : HASH) : S with type key = X.t

(** {2 Flat hashtable} *)

module Flat(X : HASH) : S with type key = X.t