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(************************************************************************)
(* * The Coq Proof Assistant / The Coq Development Team *)
(* v * INRIA, CNRS and contributors - Copyright 1999-2019 *)
(* <O___,, * (see CREDITS file for the list of authors) *)
(* \VV/ **************************************************************)
(* // * This file is distributed under the terms of the *)
(* * GNU Lesser General Public License Version 2.1 *)
(* * (see LICENSE file for the text of the license) *)
(************************************************************************)
type ('a,'r) u =
| Nil
| Cons of 'a * 'r
type 'a node = ('a,'a t) u
and 'a t = 'a node Lazy.t
let empty = Lazy.from_val Nil
let cons x s = Lazy.from_val (Cons (x, s))
let thunk = Lazy.from_fun
let rec make_node f s = match f s with
| Nil -> Nil
| Cons (x, s) -> Cons (x, make f s)
and make f s = lazy (make_node f s)
let rec force s = match Lazy.force s with
| Nil -> ()
| Cons (_, s) -> force s
let force s = force s; s
let is_empty s = match Lazy.force s with
| Nil -> true
| Cons (_, _) -> false
let peek = Lazy.force
let rec of_list = function
| [] -> empty
| x :: l -> cons x (of_list l)
let rec to_list s = match Lazy.force s with
| Nil -> []
| Cons (x, s) -> x :: (to_list s)
let rec iter f s = match Lazy.force s with
| Nil -> ()
| Cons (x, s) -> f x; iter f s
let rec map_node f = function
| Nil -> Nil
| Cons (x, s) -> Cons (f x, map f s)
and map f s = lazy (map_node f (Lazy.force s))
let rec app_node n1 s2 = match n1 with
| Nil -> Lazy.force s2
| Cons (x, s1) -> Cons (x, app s1 s2)
and app s1 s2 = lazy (app_node (Lazy.force s1) s2)
let rec fold f accu s = match Lazy.force s with
| Nil -> accu
| Cons (x, s) -> fold f (f accu x) s
let rec map_filter_node f = function
| Nil -> Nil
| Cons (x, s) ->
begin match f x with
| None -> map_filter_node f (Lazy.force s)
| Some y -> Cons (y, map_filter f s)
end
and map_filter f s = lazy (map_filter_node f (Lazy.force s))
let rec concat_node = function
| Nil -> Nil
| Cons (s, sl) -> app_node (Lazy.force s) (concat sl)
and concat (s : 'a t t) =
lazy (concat_node (Lazy.force s))
let rec concat_map_node f = function
| Nil -> Nil
| Cons (x,s) -> app_node (Lazy.force (f x)) (concat_map f s)
and concat_map f l = lazy (concat_map_node f (Lazy.force l))