(* Copyright (C) 2005, HELM Team.
 * 
 * This file is part of HELM, an Hypertextual, Electronic
 * Library of Mathematics, developed at the Computer Science
 * Department, University of Bologna, Italy.
 * 
 * HELM 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.
 * 
 * HELM 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 HELM; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston,
 * MA  02111-1307, USA.
 * 
 * For details, see the HELM World-Wide-Web page,
 * http://helm.cs.unibo.it/
 *)

exception Error of string

module type Engine =
sig
  type goal
  type proof
  type tactic

  val is_goal_closed: goal -> proof -> bool
  val goals_of_proof: proof -> goal list

  val apply_tactic:
    tactic -> proof -> goal ->
      proof * goal list * goal list (** new proof, opened goals, closed goals *)
end

module Make (E:Engine) :
sig
  type goal_switch = Open of E.goal | Closed of E.goal
  type 'a stack = 'a list
  type status =
    E.proof * ((int * goal_switch) list * E.goal list * E.goal list) stack

  type tactical =
    | Tactic of E.tactic
    | Skip

  type t =
    | Dot
    | Semicolon

    | Branch
    | Shift of int option
    | Merge

    | Select of E.goal list
    | End_select

    | Tactical of tactical

    | Qed

  val eval: t -> status -> status
  val init: E.proof -> status
end