(***********************************************************************)
  sStream.ml - simple stream with 1 - step lookahead .                   
(*                                                                     *)
  Copyright ( C ) 2002 , 2003 , 2004 , 2005 , 2006 , 2007 , 2008 , 2009 , 2010 ,
                2011 , 2012 , 2013     and Contributors       
(*                                                                     *)
  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 or see < / > .                          
(***********************************************************************)

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




*********************************************************************
                                                                     
                                                                     
 redistribute it and/or modify it under the terms of the GNU General 
                                                                     
 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.                            
                                                                     
*********************************************************************
  sStream.ml - simple stream with 1 - step lookahead .                   
  Copyright ( C ) 2002 , 2003 , 2004 , 2005 , 2006 , 2007 , 2008 , 2009 , 2010 ,
                2011 , 2012 , 2013     and Contributors       
  This file is part of SKS .   SKS is free software ; you can            
  Public License as published by the Free Software Foundation ; either
  version 2 of the License , or ( at your option ) any later version .    
  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 or see < / > .                          

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



