(*
copyright (c) 2013-2014, simon cruanes
all rights reserved.

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modification, are permitted provided that the following conditions are met:

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*)

(** {1 Batch Operations on Collections}
Define and combine operations on a collection of elements, then
run the composition of those operations on some collection. The
composition is optimized to minimize the number of intermediate
collections *)

(** {2 Definition of a Collection} *)
module type COLLECTION = sig
  type 'a t

  val empty : 'a t
  val fold : ('a -> 'b -> 'a) -> 'a -> 'b t -> 'a
  val map : ('a -> 'b) -> 'a t -> 'b t
  val filter : ('a -> bool) -> 'a t -> 'a t
  val filter_map : ('a -> 'b option) -> 'a t -> 'b t
  val flat_map : ('a -> 'b t) -> 'a t -> 'b t
end

(** {2 Definition of a Batch operations} *)
module type S = sig
  type 'a t

  type ('a,'b) op
  (** Operation that converts an ['a t] into a ['b t] *)

  val apply : ('a,'b) op -> 'a t -> 'b t
  (** Apply the operation to the collection. *)

  val apply_fold : ('a, 'b) op -> ('c -> 'b -> 'c) -> 'c -> 'a t -> 'c
  (** Apply the operation plus a fold to the collection. *)

  val apply' : 'a t -> ('a,'b) op -> 'b t
  (** Flip of {!apply} *)

  (** {6 Combinators} *)

  val id : ('a, 'a) op

  val map : ('a -> 'b) -> ('a, 'b) op

  val filter : ('a -> bool) -> ('a,'a) op

  val filter_map : ('a -> 'b option) -> ('a,'b) op

  val flat_map : ('a -> 'b t) -> ('a,'b) op

  val extern : ('a t -> 'b t) -> ('a,'b) op
  (** Use a specific function that won't be optimized *)

  val compose : ('b,'c) op -> ('a,'b) op -> ('a,'c) op
  val (>>>) : ('a,'b) op -> ('b,'c) op -> ('a,'c) op
end

(** {2 Functor} *)
module Make(C : COLLECTION) : S with type 'a t = 'a C.t