(*
This file is part of the first order theorem prover Darwin
Copyright (C) 2004, 2005
The University of Iowa
Universitaet Koblenz-Landau
This program 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.
*)
(* a counter is just an int that is repeatedly incremented by 1.
only zero and positive values are allowed,
negative values mark a counter overflow. *)
type counter =
int ref
exception OVERFLOW
let value (counter: counter) : int =
!counter
let create_with (start: int) : counter =
if start >= 0 then
ref start
else
raise OVERFLOW
let create () : counter =
create_with 0
let set (counter: counter) (value: int) : unit =
if value >= 0 then
counter := value
else
raise OVERFLOW
let inc_by (counter: counter) (increment: int) : unit =
let new_value =
!counter + increment
in
if new_value > !counter then
counter := new_value
else
raise OVERFLOW
let inc (counter: counter) : unit =
inc_by counter 1
let dec (counter: counter) : unit =
let new_value =
!counter - 1
in
if new_value < !counter then
counter := new_value
else
raise OVERFLOW
let next (counter: counter) : int =
inc counter;
value counter