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|
(************************************************************************)
(* v * The Coq Proof Assistant / The Coq Development Team *)
(* <O___,, * INRIA - CNRS - LIX - LRI - PPS - Copyright 1999-2017 *)
(* \VV/ **************************************************************)
(* // * This file is distributed under the terms of the *)
(* * GNU Lesser General Public License Version 2.1 *)
(************************************************************************)
exception Empty
type 'a t = {
face : 'a list;
rear : 'a list;
lenf : int;
lenr : int;
}
let rec split i accu l = match l with
| [] ->
if Int.equal i 0 then (accu, []) else invalid_arg "split"
| t :: q ->
if Int.equal i 0 then (accu, l)
else split (pred i) (t :: accu) q
let balance q =
let avg = (q.lenf + q.lenr) / 2 in
let dif = q.lenf + q.lenr - avg in
if q.lenf > succ (2 * q.lenr) then
let (ff, fr) = split avg [] q.face in
{ face = List.rev ff ; rear = q.rear @ List.rev fr; lenf = avg; lenr = dif }
else if q.lenr > succ (2 * q.lenf) then
let (rf, rr) = split avg [] q.rear in
{ face = q.face @ List.rev rr ; rear = List.rev rf; lenf = dif; lenr = avg }
else q
let empty = {
face = [];
rear = [];
lenf = 0;
lenr = 0;
}
let lcons x q =
balance { q with lenf = succ q.lenf; face = x :: q.face }
let lhd q = match q.face with
| [] ->
begin match q.rear with
| [] -> raise Empty
| t :: _ -> t
end
| t :: _ -> t
let ltl q = match q.face with
| [] ->
begin match q.rear with
| [] -> raise Empty
| t :: _ -> empty
end
| t :: r -> balance { q with lenf = pred q.lenf; face = r }
let rcons x q =
balance { q with lenr = succ q.lenr; rear = x :: q.rear }
let rhd q = match q.rear with
| [] ->
begin match q.face with
| [] -> raise Empty
| t :: r -> t
end
| t :: _ -> t
let rtl q = match q.rear with
| [] ->
begin match q.face with
| [] -> raise Empty
| t :: r -> empty
end
| t :: r ->
balance { q with lenr = pred q.lenr; rear = r }
let rev q = {
face = q.rear;
rear = q.face;
lenf = q.lenr;
lenr = q.lenf;
}
let length q = q.lenf + q.lenr
let is_empty q = Int.equal (length q) 0
let filter f q =
let fold (accu, len) x = if f x then (x :: accu, succ len) else (accu, len) in
let (rf, lenf) = List.fold_left fold ([], 0) q.face in
let (rr, lenr) = List.fold_left fold ([], 0) q.rear in
balance { face = List.rev rf; rear = List.rev rr; lenf = lenf; lenr = lenr }
|
