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

(** {1 Consumable generators} *)

(** This structure is inspired from Ocaml Batteries' BatEnum.t. It features
    restartable generators. *)

exception EOG
  (** End of Generation *)

type 'a t = unit -> 'a generator
  (** An enum is a generator of generators *)
and 'a generator = unit -> 'a
  (** A generator may be called several times, yielding the next value
      each time. It raises EOG when it reaches the end. *)

(** {2 Generator functions} *)

val start : 'a t -> 'a generator
  (** Create a new generator *)

val next : 'a generator -> 'a
  (** Get next element, or raise EOG *)

val junk : 'a generator -> unit
  (** Drop element *)

(** {2 Basic constructors} *)

val empty : 'a t
  (** Enmpty enum *)

val singleton : 'a -> 'a t
  (** One-element enum *)

val repeat : 'a -> 'a t
  (** Repeat same element endlessly *)

val iterate : 'a -> ('a -> 'a) -> 'a t
  (** [iterate x f] is [[x; f x; f (f x); f (f (f x)); ...]] *)

(** {2 Basic combinators} *)

val is_empty : _ t -> bool
  (** Check whether the enum is empty *)

val fold : ('b -> 'a -> 'b) -> 'b -> 'a t -> 'b
  (** Fold on the generator *)

val iter : ('a -> unit) -> 'a t -> unit
  (** Iterate on the enum *)

val length : _ t -> int
  (** Length of an enum (linear time) *)

val map : ('a -> 'b) -> 'a t -> 'b t
  (** Lazy map *)

val append : 'a t -> 'a t -> 'a t
  (** Append the two enums *)

val cycle : 'a t -> 'a t
  (** Cycle through the enum, endlessly. The enum must not be empty. *)

val flatten : 'a t t -> 'a t
  (** Flatten the enum of enum *)

val flatMap : ('a -> 'b t) -> 'a t -> 'b t
  (** Monadic bind *)

val take : int -> 'a t -> 'a t
  (** Take at most n elements *)

val drop : int -> 'a t -> 'a t
  (** Drop n elements *)

val filter : ('a -> bool) -> 'a t -> 'a t
  (** Filter out elements that do not satisfy the predicate. The outer
      enum must be finite. *)

val takeWhile : ('a -> bool) -> 'a t -> 'a t
  (** Take elements while they satisfy the predicate *)

val dropWhile : ('a -> bool) -> 'a t -> 'a t
  (** Drop elements while they satisfy the predicate *)

val filterMap : ('a -> 'b option) -> 'a t -> 'b t
  (** Maps some elements to 'b, drop the other ones *)

val zipWith : ('a -> 'b -> 'c) -> 'a t -> 'b t -> 'c t
  (** Combine common part of the enums (stops when one is exhausted) *)

val zip : 'a t -> 'b t -> ('a * 'b) t
  (** Zip together the common part of the enums *)

val zipIndex : 'a t -> (int * 'a) t
  (** Zip elements with their index in the enum *)

(** {2 Complex combinators} *)

val round_robin : 'a t t -> 'a t
  (** Pick elements fairly in each sub-enum *)

val persistent : 'a generator -> 'a t
  (** Store content of the generator in memory, to be able to iterate on it
      several times later *)

val tee : ?n:int -> 'a t -> 'a generator t
  (** Split the enum into [n] generators in a fair way. Elements with
      [index = k mod n] with go to the k-th enum. [n] defaults value
      is 2. *)

val interleave : 'a t -> 'a t -> 'a t
  (** [interleave a b] yields an element of [a], then an element of [b],
      and so on until the end of [a] or [b] is reached. *)

val intersperse : 'a -> 'a t -> 'a t
  (** Put the separator element between all elements of the given enum *)

val product : 'a t -> 'b t -> ('a * 'b) t
  (** Cartesian product *)

val permutations : 'a t -> 'a t t
  (** Permutations of the enum *)

val combinations : int -> 'a t -> 'a t t
  (** Combinations of given length *)

(** {2 Basic conversion functions} *)

val of_list : 'a list -> 'a t
  (** Enumerate the list *)

val to_list : 'a t -> 'a list
  (** non tail-call trasnformation to list *)

val to_rev_list : 'a t -> 'a list
  (** Tail call conversion to list, in reverse order *)

val int_range : int -> int -> int t

module Infix : sig
  val (@@) : 'a t -> 'a t -> 'a t
  val (>>=) : 'a t -> ('a -> 'b t) -> 'b t
  val (--) : int -> int -> int t
  val (|>) : 'a -> ('a -> 'b) -> 'b
end