(***********************************************************************)
(*                                                                     *)
(*                           Objective Caml                            *)
(*                                                                     *)
(* Xavier Leroy and Jerome Vouillon, projet Cristal, INRIA Rocquencourt*)
(*                                                                     *)
(*  Copyright 1996 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.               *)
(*                                                                     *)
(***********************************************************************)

(* $Id$ *)

(* Basic operations on core types *)

open Types

(**** Type level management ****)

let generic_level = 100000000

(* Used to mark a type during a traversal. *)
let lowest_level = 0
let pivot_level = 2 * lowest_level - 1
    (* pivot_level - lowest_level < lowest_level *)

(**** Some type creators ****)

let new_id = ref (-1)

let newty2 level desc  =
  incr new_id; { desc = desc; level = level; id = !new_id }
let newgenty desc      = newty2 generic_level desc
let newgenvar ()       = newgenty Tvar
(*
let newmarkedvar level =
  incr new_id; { desc = Tvar; level = pivot_level - level; id = !new_id }
let newmarkedgenvar () =
  incr new_id;
  { desc = Tvar; level = pivot_level - generic_level; id = !new_id }
*)

(**** Representative of a type ****)

let rec field_kind_repr =
  function
    Fvar {contents = Some kind} -> field_kind_repr kind
  | kind                        -> kind

let rec repr =
  function
    {desc = Tlink t'} ->
      (* 
         We do no path compression. Path compression does not seem to
         improve notably efficiency, and it prevents from changing a
         [Tlink] into another type (for instance, for undoing a
         unification).
      *)
      repr t'
  | {desc = Tfield (_, k, _, t')} when field_kind_repr k = Fabsent ->
      repr t'
  | t -> t

let rec commu_repr = function
    Clink r when !r <> Cunknown -> commu_repr !r
  | c -> c

let rec row_field_repr = function
    Reither(_, _, _, {contents = Some fi}) -> row_field_repr fi
  | fi -> fi

let rec row_repr row =
  match (repr row.row_more).desc with
  | Tvariant row' ->
      let row' = row_repr row' in
      {row' with row_fields = row.row_fields @ row'.row_fields}
  | _ -> row

let rec row_more row =
  match repr row.row_more with
  | {desc=Tvariant row'} -> row_more row'
  | ty -> ty

let static_row row =
  let row = row_repr row in
  row.row_closed &&
  List.for_all
    (fun (_,f) -> match row_field_repr f with Reither _ -> false | _ -> true)
    row.row_fields

let hash_variant s =
  let accu = ref 0 in
  for i = 0 to String.length s - 1 do
    accu := 223 * !accu + Char.code s.[i]
  done;
  (* reduce to 31 bits *)
  accu := !accu land (1 lsl 31 - 1);
  (* make it signed for 64 bits architectures *)
  if !accu > 0x3FFFFFFF then !accu - (1 lsl 31) else !accu


                  (**********************************)
                  (*  Utilities for type traversal  *)
                  (**********************************)

let rec iter_row f row =
  List.iter
    (fun (_, fi) ->
      match row_field_repr fi with
      | Rpresent(Some ty) -> f ty
      | Reither(_, tl, _, _) -> List.iter f tl
      | _ -> ())
    row.row_fields;
  match (repr row.row_more).desc with
    Tvariant row -> iter_row f row
  | Tvar | Tnil ->
      Misc.may (fun (_,l) -> List.iter f l) row.row_name;
      List.iter f row.row_bound
  | _ -> assert false

let iter_type_expr f ty =
  match ty.desc with
    Tvar                -> ()
  | Tarrow (_, ty1, ty2, _) -> f ty1; f ty2
  | Ttuple l            -> List.iter f l
  | Tconstr (_, l, _)   -> List.iter f l
  | Tobject(ty, {contents = Some (_, p)})
                        -> f ty; List.iter f p
  | Tobject (ty, _)     -> f ty
  | Tvariant row        -> iter_row f row; f (row_more row)
  | Tfield (_, _, ty1, ty2) -> f ty1; f ty2
  | Tnil                -> ()
  | Tlink ty            -> f ty
  | Tsubst ty           -> f ty

let saved_desc = ref []
  (* Saved association of generic nodes with their description. *)

let save_desc ty desc = 
  saved_desc := (ty, desc)::!saved_desc

(* Restored type descriptions. *)
let cleanup_types () =
  List.iter (fun (ty, desc) -> ty.desc <- desc) !saved_desc;
  saved_desc := []

(* Mark a type. *)
let rec mark_type ty =
  let ty = repr ty in
  if ty.level >= lowest_level then begin
    ty.level <- pivot_level - ty.level;
    iter_type_expr mark_type ty
  end

let mark_type_node ty =
  let ty = repr ty in
  if ty.level >= lowest_level then begin
    ty.level <- pivot_level - ty.level;
  end

let mark_type_params ty =
  iter_type_expr mark_type ty

(* Remove marks from a type. *)
let rec unmark_type ty =
  let ty = repr ty in
  if ty.level < lowest_level then begin
    ty.level <- pivot_level - ty.level;
    iter_type_expr unmark_type ty
  end

let unmark_type_decl decl =
  List.iter unmark_type decl.type_params;
  begin match decl.type_kind with
    Type_abstract -> ()
  | Type_variant cstrs ->
      List.iter (fun (c, tl) -> List.iter unmark_type tl) cstrs
  | Type_record(lbls, rep) ->
      List.iter (fun (c, mut, t) -> unmark_type t) lbls
  end;
  begin match decl.type_manifest with
    None    -> ()
  | Some ty -> unmark_type ty
  end

let unmark_class_signature sign =
  unmark_type sign.cty_self;
  Vars.iter (fun l (m, t) -> unmark_type t) sign.cty_vars

let rec unmark_class_type =
  function
    Tcty_constr (p, tyl, cty) ->
      List.iter unmark_type tyl; unmark_class_type cty
  | Tcty_signature sign ->
      unmark_class_signature sign
  | Tcty_fun (_, ty, cty) ->
      unmark_type ty; unmark_class_type cty


                  (*******************************************)
                  (*  Memorization of abbreviation expansion *)
                  (*******************************************)

let memo = ref []
        (* Contains the list of saved abbreviation expansions. *)

let cleanup_abbrev () =
        (* Remove all memorized abbreviation expansions. *)
  List.iter (fun abbr -> abbr := Mnil) !memo;
  memo := []

let memorize_abbrev mem path v v' =
        (* Memorize the expansion of an abbreviation. *)
  (* assert
    begin match (repr v').desc with
      Tconstr (path', _, _) when Path.same path path'-> false
    | _ -> true
    end; *)
  mem := Mcons (path, v, v', !mem);
  memo := mem :: !memo

let rec forget_abbrev_rec mem path =
  match mem with
    Mnil ->
      assert false
  | Mcons (path', _, _, rem) when Path.same path path' ->
      rem 
  | Mcons (path, v, v', rem) ->
      Mcons (path, v, v', forget_abbrev_rec rem path)
  | Mlink mem' ->
      mem' := forget_abbrev_rec !mem' path;
      raise Exit

let forget_abbrev mem path =
  try mem := forget_abbrev_rec !mem path with Exit -> ()


                  (**********************************)
                  (*  Utilities for labels          *)
                  (**********************************)

let is_optional l =
  String.length l > 0 && l.[0] = '?'

let label_name l =
  if is_optional l then String.sub l 1 (String.length l - 1)
                   else l

let rec extract_label_aux hd l = function
    [] -> raise Not_found
  | (l',t as p) :: ls ->
      if label_name l' = l then (l', t, List.rev hd, ls)
      else extract_label_aux (p::hd) l ls

let extract_label l ls = extract_label_aux [] l ls