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(*
Copyright © 2011 MLstate

This file is part of OPA.

OPA is free software: you can redistribute it and/or modify it under the
terms of the GNU Affero General Public License, version 3, as published by
the Free Software Foundation.

OPA is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for
more details.

You should have received a copy of the GNU Affero General Public License
along with OPA. If not, see <http://www.gnu.org/licenses/>.
*)
(* cf mli *)
(* guidlines: define step by step whenever you need, in the same order than in Base.List *)
module List = Base.List
type 'a t = 'a * 'a list
external unwrap : 'a t -> 'a list = "%identity"
let wrap = function
  | t::q -> t, q
  | _ -> invalid_arg "HdList.wrap"
let singleton a = a, []

let length (_, l) = succ (List.length l)
let hd = fst
let tl = snd

let last (a, l) =
  match l with
  | [] -> a
  | tl -> hd (wrap (List.rev tl))

let nth (hd, tl) i = if i = 0 then hd else List.nth tl (pred i)
let rev (hd, tl) = wrap (List.rev (hd::tl))

let iter f (hd, tl) = f hd; List.iter f tl
let map f (hd, tl) = f hd, List.map f tl

let fold_left f acc (hd, tl) = List.fold_left f (f acc hd) tl
let fold_right f acc (hd, tl) =
  let tl = List.rev tl in
  let acc = List.fold_left f acc tl in
  f acc hd
  (* List.fold_left f acc (rev hdl) with some more tuple cons/decons *)

let reduce_left f (hd, tl) = List.fold_left f hd tl
let reduce_right f hdl = reduce_left f (rev hdl)

let fold_left_map f acc (hd, tl) =
  let acc, hd = f acc hd in
  let acc, tl = List.fold_left_map f acc tl in
  acc, (hd, tl)
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