(* 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/
 *)

type coerc_carr = Uri of UriManager.uri | Sort of Cic.sort | Term of Cic.term
exception EqCarrNotImplemented of string Lazy.t
exception EqCarrOnNonMetaClosed

let db = ref []
let use_coercions = ref true

let coerc_carr_of_term t =
  try
    Uri (CicUtil.uri_of_term t)
  with Invalid_argument _ ->
    match t with
    | Cic.Sort s -> Sort s
    | t -> Term t
;;

let eq_carr src tgt =
  match src, tgt with
  | Uri src, Uri tgt -> UriManager.eq src tgt
  | Sort (Cic.Type _), Sort (Cic.Type _) -> true
  | Sort src, Sort tgt when src = tgt -> true
  | Term t1, Term t2 ->
    if CicUtil.is_meta_closed t1 && CicUtil.is_meta_closed t2 then
      raise 
        (EqCarrNotImplemented 
          (lazy ("Unsupported carr for coercions: " ^ 
            CicPp.ppterm t1 ^ " or " ^ CicPp.ppterm t2)))
    else raise EqCarrOnNonMetaClosed
  | _, _ -> false

let name_of_carr = function
  | Uri u -> UriManager.name_of_uri u
  | Sort s -> CicPp.ppsort s
  | Term _ -> assert false
  

let to_list () =
  !db

let add_coercion c =
  db := c :: !db

let remove_coercion p = 
  db := List.filter (fun u -> not(p u)) !db

let find_coercion f =
  if !use_coercions then
    List.map (fun (_,_,x) -> x) (List.filter (fun (s,t,_) -> f (s,t)) !db)
  else []