(************************************************************************)
(* This file is part of SKS.  SKS is free software; you can
   redistribute it and/or modify it under the terms of the GNU General
   Public License as published by the Free Software Foundation; either
   version 2 of the License, or (at your option) any 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
   General Public License for more details.

   You should have received a copy of the GNU 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 *)
(***********************************************************************)

(** simple stream with 1-step lookahead. *)

type 'b sstream = { mutable first: 'b option;
		    next: unit -> 'b option;
		  }

let make ?first next = { first = first;
			 next = next;
		       }

let next s =
  match s.first with
      None -> s.next ()
    | v ->
	s.first <- None;
	v

let peek s = 
  if s.first = None 
  then s.first <- s.next ();
  s.first

let junk s = 
  if s.first = None 
  then ignore (s.next ())
  else s.first <- None