(**************************************************************************)
(*                                                                        *)
(*  Menhir                                                                *)
(*                                                                        *)
(*  François Pottier and Yann Régis-Gianas, INRIA Rocquencourt            *)
(*                                                                        *)
(*  Copyright 2005 Institut National de Recherche en Informatique et      *)
(*  en Automatique. All rights reserved. This file is distributed         *)
(*  under the terms of the Q Public License version 1.0, with the         *)
(*  change described in file LICENSE.                                     *)
(*                                                                        *)
(**************************************************************************)

(* These are the operations required of lookahead sets during
   a closure computation. This signature is exploited by the
   functor [Item.Closure]. *)

module type S = sig

  (* The type of lookahead sets. *)
  type t

  (* The empty lookahead set. Redundant with the following, but
     convenient. *)
  val empty: t

  (* A concrete, constant set of terminal symbols. *)
  val constant: Grammar.TerminalSet.t -> t

  (* [union s1 s2] returns the union of [s1] and [s2].  *)
  val union: t -> t -> t

end