ext_stack.ml

(* Copyright (C) 2017 Hongbo Zhang, Authors of ReScript
 * 
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * In addition to the permissions granted to you by the LGPL, you may combine
 * or link a "work that uses the Library" with a publicly distributed version
 * of this file to produce a combined library or application, then distribute
 * that combined work under the terms of your choosing, with no requirement
 * to comply with the obligations normally placed on you by section 4 of the
 * LGPL version 3 (or the corresponding section of a later version of the LGPL
 * should you choose to use a later version).
 *
 * This program 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 Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. *)

type 'a t = 'a list ref

let create_ref_empty () = ref []

let ref_top x =
  match !x with y :: _ -> y | _ -> invalid_arg "Ext_list.ref_top"

let ref_empty x = match !x with [] -> true | _ -> false

let ref_push x refs = refs := x :: !refs

let ref_pop refs =
  match !refs with
  | [] -> invalid_arg "Ext_list.ref_pop"
  | x :: rest ->
      refs := rest;
      x