pretyping.ml

(************************************************************************)
(*  v      *   The Coq Proof Assistant  /  The Coq Development Team     *)
(* <O___,, *   INRIA - CNRS - LIX - LRI - PPS - Copyright 1999-2012     *)
(*   \VV/  **************************************************************)
(*    //   *      This file is distributed under the terms of the       *)
(*         *       GNU Lesser General Public License Version 2.1        *)
(************************************************************************)

(* This file contains the syntax-directed part of the type inference
   algorithm introduced by Murthy in Coq V5.10, 1995; the type
   inference algorithm was initially developed in a file named trad.ml
   which formerly contained a simple concrete-to-abstract syntax
   translation function introduced in CoC V4.10 for implementing the
   "exact" tactic, 1989 *)
(* Support for typing term in Ltac environment by David Delahaye, 2000 *)
(* Type inference algorithm made a functor of the coercion and
   pattern-matching compilation by Matthieu Sozeau, March 2006 *)
(* Fixpoint guard index computation by Pierre Letouzey, July 2007 *)

(* Structural maintainer: Hugo Herbelin *)
(* Secondary maintenance: collective *)


open Compat
open Pp
open Util
open Names
open Sign
open Evd
open Term
open Termops
open Reductionops
open Environ
open Type_errors
open Typeops
open Libnames
open Nameops
open Classops
open List
open Recordops
open Evarutil
open Pretype_errors
open Glob_term
open Evarconv
open Pattern

type typing_constraint = OfType of types option | IsType
type var_map = (identifier * constr_under_binders) list
type unbound_ltac_var_map = (identifier * identifier option) list
type ltac_var_map = var_map * unbound_ltac_var_map
type glob_constr_ltac_closure = ltac_var_map * glob_constr
type pure_open_constr = evar_map * constr

(************************************************************************)
(* This concerns Cases *)
open Declarations
open Inductive
open Inductiveops

(************************************************************************)

(* An auxiliary function for searching for fixpoint guard indexes *)

exception Found of int array

let search_guard loc env possible_indexes fixdefs =
  (* Standard situation with only one possibility for each fix. *)
  (* We treat it separately in order to get proper error msg. *)
  if List.for_all (fun l->1=List.length l) possible_indexes then
    let indexes = Array.of_list (List.map List.hd possible_indexes) in
    let fix = ((indexes, 0),fixdefs) in
    (try check_fix env fix with
       | e -> if loc = dummy_loc then raise e else Loc.raise loc e);
    indexes
  else
    (* we now search recursively amoungst all combinations *)
    (try
       List.iter
	 (fun l ->
	    let indexes = Array.of_list l in
	    let fix = ((indexes, 0),fixdefs) in
	    try check_fix env fix; raise (Found indexes)
	    with TypeError _ -> ())
	 (list_combinations possible_indexes);
       let errmsg = "Cannot guess decreasing argument of fix." in
       if loc = dummy_loc then error errmsg else
	 user_err_loc (loc,"search_guard", Pp.str errmsg)
     with Found indexes -> indexes)

(* To embed constr in glob_constr *)
let ((constr_in : constr -> Dyn.t),
     (constr_out : Dyn.t -> constr)) = Dyn.create "constr"

(** Miscellaneous interpretation functions *)

let interp_sort = function
  | GProp c -> Prop c
  | GType _ -> new_Type_sort ()

let interp_elimination_sort = function
  | GProp Null -> InProp
  | GProp Pos  -> InSet
  | GType _ -> InType

let resolve_evars env evdref fail_evar resolve_classes =
  if resolve_classes then
    evdref := (Typeclasses.resolve_typeclasses ~filter:Typeclasses.no_goals
		 ~split:true ~fail:fail_evar env !evdref);
  (* Resolve eagerly, potentially making wrong choices *)
  evdref := (try consider_remaining_unif_problems
	       ~ts:(Typeclasses.classes_transparent_state ()) env !evdref
	     with e -> if fail_evar then raise e else !evdref)

let solve_remaining_evars fail_evar use_classes hook env initial_sigma (evd,c) =
  let evdref = ref evd in
  resolve_evars env evdref fail_evar use_classes;
  let rec proc_rec c =
    let c = Reductionops.whd_evar !evdref c in
    match kind_of_term c with
    | Evar (evk,args as ev) when not (Evd.mem initial_sigma evk) ->
        let sigma = !evdref in
	(try
	   let c = hook env sigma ev in
	   evdref := Evd.define evk c !evdref;
	   c
	 with Exit ->
           if fail_evar then
	     let evi = Evd.find_undefined sigma evk in
             let (loc,src) = evar_source evk !evdref in
	     Pretype_errors.error_unsolvable_implicit loc env sigma evi src None
           else
             c)
    | _ -> map_constr proc_rec c in
  let c = proc_rec c in
  (* Side-effect *)
  !evdref,c

module type S =
sig

  module Cases : Cases.S

  (* Allow references to syntaxically inexistent variables (i.e., if applied on an inductive) *)
  val allow_anonymous_refs : bool ref

  (* Generic call to the interpreter from glob_constr to open_constr, leaving
     unresolved holes as evars and returning the typing contexts of
     these evars. Work as [understand_gen] for the rest. *)

  val understand_tcc : ?resolve_classes:bool ->
    evar_map -> env -> ?expected_type:types -> glob_constr -> open_constr

  val understand_tcc_evars : ?fail_evar:bool -> ?resolve_classes:bool ->
    evar_map ref -> env -> typing_constraint -> glob_constr -> constr

  (* More general entry point with evars from ltac *)

  (* Generic call to the interpreter from glob_constr to constr, failing
     unresolved holes in the glob_constr cannot be instantiated.

     In [understand_ltac expand_evars sigma env ltac_env constraint c],

     resolve_classes : launch typeclass resolution after typechecking.
     expand_evars : expand inferred evars by their value if any
     sigma : initial set of existential variables (typically dependent subgoals)
     ltac_env : partial substitution of variables (used for the tactic language)
     constraint : tell if interpreted as a possibly constrained term or a type
  *)

  val understand_ltac : ?resolve_classes:bool ->
    bool -> evar_map -> env -> ltac_var_map ->
    typing_constraint -> glob_constr -> pure_open_constr

  (* Standard call to get a constr from a glob_constr, resolving implicit args *)

  val understand : evar_map -> env -> ?expected_type:Term.types ->
    glob_constr -> constr

  (* Idem but the glob_constr is intended to be a type *)

  val understand_type : evar_map -> env -> glob_constr -> constr

  (* A generalization of the two previous case *)

  val understand_gen : typing_constraint -> evar_map -> env ->
    glob_constr -> constr

  (* Idem but returns the judgment of the understood term *)

  val understand_judgment : evar_map -> env -> glob_constr -> unsafe_judgment

  (* Idem but do not fail on unresolved evars *)

  val understand_judgment_tcc : evar_map ref -> env -> glob_constr -> unsafe_judgment

  (*i*)
  (* Internal of Pretyping...
   * Unused outside, but useful for debugging
   *)
  val pretype :
    type_constraint -> env -> evar_map ref ->
    ltac_var_map -> glob_constr -> unsafe_judgment

  val pretype_type :
    val_constraint -> env -> evar_map ref ->
    ltac_var_map -> glob_constr -> unsafe_type_judgment

  val pretype_gen :
    bool -> bool -> bool -> evar_map ref -> env ->
    ltac_var_map -> typing_constraint -> glob_constr -> constr

    (*i*)
end

module Pretyping_F (Coercion : Coercion.S) = struct

  module Cases = Cases.Cases_F(Coercion)

  (* Allow references to syntaxically inexistent variables (i.e., if applied on an inductive) *)
  let allow_anonymous_refs = ref false

  let evd_comb0 f evdref =
    let (evd',x) = f !evdref in
      evdref := evd';
      x

  let evd_comb1 f evdref x =
    let (evd',y) = f !evdref x in
      evdref := evd';
      y

  let evd_comb2 f evdref x y =
    let (evd',z) = f !evdref x y in
      evdref := evd';
      z

  let evd_comb3 f evdref x y z =
    let (evd',t) = f !evdref x y z in
      evdref := evd';
      t

  let mt_evd = Evd.empty

  (* Utilisé pour inférer le prédicat des Cases *)
  (* Semble exagérement fort *)
  (* Faudra préférer une unification entre les types de toutes les clauses *)
  (* et autoriser des ? à rester dans le résultat de l'unification *)

  let evar_type_fixpoint loc env evdref lna lar vdefj =
    let lt = Array.length vdefj in
      if Array.length lar = lt then
	for i = 0 to lt-1 do
          if not (e_cumul env evdref (vdefj.(i)).uj_type
		    (lift lt lar.(i))) then
            error_ill_typed_rec_body_loc loc env !evdref
              i lna vdefj lar
	done

  (* coerce to tycon if any *)
  let inh_conv_coerce_to_tycon loc env evdref j = function
    | None -> j
    | Some t -> evd_comb2 (Coercion.inh_conv_coerce_to loc env) evdref j t

  let push_rels vars env = List.fold_right push_rel vars env

  (* used to enforce a name in Lambda when the type constraints itself
     is named, hence possibly dependent *)

  let orelse_name name name' = match name with
    | Anonymous -> name'
    | _ -> name

  let invert_ltac_bound_name env id0 id =
    try mkRel (pi1 (lookup_rel_id id (rel_context env)))
    with Not_found ->
      errorlabstrm "" (str "Ltac variable " ++ pr_id id0 ++
	str " depends on pattern variable name " ++ pr_id id ++
	str " which is not bound in current context.")

  let protected_get_type_of env sigma c =
    try Retyping.get_type_of env sigma c
    with Anomaly _ ->
      errorlabstrm "" (str "Cannot reinterpret " ++ quote (print_constr c) ++ str " in the current environment.")

  let pretype_id loc env sigma (lvar,unbndltacvars) id =
    (* Look for the binder of [id] *)
    try
      let (n,_,typ) = lookup_rel_id id (rel_context env) in
      { uj_val  = mkRel n; uj_type = lift n typ }
    with Not_found ->
    (* Check if [id] is an ltac variable *)
    try
      let (ids,c) = List.assoc id lvar in
      let subst = List.map (invert_ltac_bound_name env id) ids in
      let c = substl subst c in
      { uj_val = c; uj_type = protected_get_type_of env sigma c }
    with Not_found ->
    (* Check if [id] is a section or goal variable *)
    try
      let (_,_,typ) = lookup_named id env in
      { uj_val  = mkVar id; uj_type = typ }
    with Not_found ->
    (* [id] not found, build nice error message if [id] yet known from ltac *)
    try
      match List.assoc id unbndltacvars with
      | None -> user_err_loc (loc,"",
	  str "Variable " ++ pr_id id ++ str " should be bound to a term.")
      | Some id0 -> Pretype_errors.error_var_not_found_loc loc id0
    with Not_found ->
    (* [id] not found, standard error message *)
      error_var_not_found_loc loc id

  let evar_kind_of_term sigma c =
    kind_of_term (whd_evar sigma c)

  (*************************************************************************)
  (* Main pretyping function                                               *)

  let pretype_ref evdref env ref =
    let c = constr_of_global ref in
      make_judge c (Retyping.get_type_of env Evd.empty c)
  let pretype_ref loc evdref env = function
    | VarRef id ->
        (* Section variable *)
        (try let (_,_,ty) = lookup_named id env in make_judge (mkVar id) ty
         with Not_found ->
           (* This may happen if env is a goal env and section variables have
              been cleared - section variables should be different from goal
              variables *)
           Pretype_errors.error_var_not_found_loc loc id)
    | ref ->
        let c = constr_of_global ref in
        make_judge c (Retyping.get_type_of env Evd.empty c)

  let pretype_sort evdref = function
    | GProp c -> judge_of_prop_contents c
    | GType _ -> evd_comb0 judge_of_new_Type evdref

  exception Found of fixpoint

  let new_type_evar evdref env loc =
    evd_comb0 (fun evd -> Evarutil.new_type_evar evd env ~src:(loc,InternalHole)) evdref

  (* [pretype tycon env evdref lvar lmeta cstr] attempts to type [cstr] *)
  (* in environment [env], with existential variables [evdref] and *)
  (* the type constraint tycon *)
  let rec pretype (tycon : type_constraint) env evdref lvar = function
    | GRef (loc,ref) ->
	inh_conv_coerce_to_tycon loc env evdref
	  (pretype_ref loc evdref env ref)
	  tycon

    | GVar (loc, id) ->
	inh_conv_coerce_to_tycon loc env evdref
	  (pretype_id loc env !evdref lvar id)
	  tycon

    | GEvar (loc, evk, instopt) ->
	(* Ne faudrait-il pas s'assurer que hyps est bien un
	   sous-contexte du contexte courant, et qu'il n'y a pas de Rel "caché" *)
	let hyps = evar_filtered_context (Evd.find !evdref evk) in
	let args = match instopt with
          | None -> instance_from_named_context hyps
          | Some inst -> failwith "Evar subtitutions not implemented" in
	let c = mkEvar (evk, args) in
	let j = (Retyping.get_judgment_of env !evdref c) in
	  inh_conv_coerce_to_tycon loc env evdref j tycon

    | GPatVar (loc,(someta,n)) ->
	let ty =
          match tycon with
            | Some (None, ty) -> ty
            | None | Some _ -> new_type_evar evdref env loc in
        let k = MatchingVar (someta,n) in
	{ uj_val = e_new_evar evdref env ~src:(loc,k) ty; uj_type = ty }

    | GHole (loc,k) ->
	let ty =
          match tycon with
            | Some (None, ty) -> ty
            | None | Some _ ->
		new_type_evar evdref env loc in
	  { uj_val = e_new_evar evdref env ~src:(loc,k) ty; uj_type = ty }

    | GRec (loc,fixkind,names,bl,lar,vdef) ->
	let rec type_bl env ctxt = function
            [] -> ctxt
          | (na,bk,None,ty)::bl ->
              let ty' = pretype_type empty_valcon env evdref lvar ty in
              let dcl = (na,None,ty'.utj_val) in
		type_bl (push_rel dcl env) (add_rel_decl dcl ctxt) bl
          | (na,bk,Some bd,ty)::bl ->
              let ty' = pretype_type empty_valcon env evdref lvar ty in
              let bd' = pretype (mk_tycon ty'.utj_val) env evdref lvar ty in
              let dcl = (na,Some bd'.uj_val,ty'.utj_val) in
		type_bl (push_rel dcl env) (add_rel_decl dcl ctxt) bl in
	let ctxtv = Array.map (type_bl env empty_rel_context) bl in
	let larj =
          array_map2
            (fun e ar ->
               pretype_type empty_valcon (push_rel_context e env) evdref lvar ar)
            ctxtv lar in
	let lara = Array.map (fun a -> a.utj_val) larj in
	let ftys = array_map2 (fun e a -> it_mkProd_or_LetIn a e) ctxtv lara in
	let nbfix = Array.length lar in
	let names = Array.map (fun id -> Name id) names in
	  (* Note: bodies are not used by push_rec_types, so [||] is safe *)
	let newenv = push_rec_types (names,ftys,[||]) env in
	let vdefj =
	  array_map2_i
	    (fun i ctxt def ->
               (* we lift nbfix times the type in tycon, because of
		* the nbfix variables pushed to newenv *)
               let (ctxt,ty) =
		 decompose_prod_n_assum (rel_context_length ctxt)
                   (lift nbfix ftys.(i)) in
               let nenv = push_rel_context ctxt newenv in
               let j = pretype (mk_tycon ty) nenv evdref lvar def in
		 { uj_val = it_mkLambda_or_LetIn j.uj_val ctxt;
		   uj_type = it_mkProd_or_LetIn j.uj_type ctxt })
            ctxtv vdef in
	evar_type_fixpoint loc env evdref names ftys vdefj;
	let ftys = Array.map (nf_evar !evdref) ftys in
	let fdefs = Array.map (fun x -> nf_evar !evdref (j_val x)) vdefj in
 	let fixj = match fixkind with
	  | GFix (vn,i) ->
	      (* First, let's find the guard indexes. *)
	      (* If recursive argument was not given by user, we try all args.
	         An earlier approach was to look only for inductive arguments,
		 but doing it properly involves delta-reduction, and it finally
                 doesn't seem worth the effort (except for huge mutual
		 fixpoints ?) *)
	      let possible_indexes = Array.to_list (Array.mapi
		(fun i (n,_) -> match n with
		   | Some n -> [n]
		   | None -> list_map_i (fun i _ -> i) 0 ctxtv.(i))
		vn)
	      in
	      let fixdecls = (names,ftys,fdefs) in
	      let indexes = search_guard loc env possible_indexes fixdecls in
	      make_judge (mkFix ((indexes,i),fixdecls)) ftys.(i)
	  | GCoFix i ->
	      let cofix = (i,(names,ftys,fdefs)) in
	      (try check_cofix env cofix with e -> Loc.raise loc e);
	      make_judge (mkCoFix cofix) ftys.(i) in
	inh_conv_coerce_to_tycon loc env evdref fixj tycon

    | GSort (loc,s) ->
	let j = pretype_sort evdref s in
	  inh_conv_coerce_to_tycon loc env evdref j tycon

    | GApp (loc,f,args) ->
	let fj = pretype empty_tycon env evdref lvar f in
 	let floc = loc_of_glob_constr f in
	let rec apply_rec env n resj = function
	  | [] -> resj
	  | c::rest ->
	      let argloc = loc_of_glob_constr c in
	      let resj = evd_comb1 (Coercion.inh_app_fun env) evdref resj in
              let resty = whd_betadeltaiota env !evdref resj.uj_type in
      		match kind_of_term resty with
		  | Prod (na,c1,c2) ->
		      let hj = pretype (mk_tycon c1) env evdref lvar c in
		      let value, typ = applist (j_val resj, [j_val hj]), subst1 hj.uj_val c2 in
			apply_rec env (n+1)
			  { uj_val = value;
			    uj_type = typ }
			  rest
		  | _ ->
		      let hj = pretype empty_tycon env evdref lvar c in
			error_cant_apply_not_functional_loc
			  (join_loc floc argloc) env !evdref
	      		  resj [hj]
	in
	let resj = apply_rec env 1 fj args in
	let resj =
	  match evar_kind_of_term !evdref resj.uj_val with
	  | App (f,args) ->
              let f = whd_evar !evdref f in
              begin match kind_of_term f with
              | Ind _ | Const _
		  when isInd f or has_polymorphic_type (destConst f)
		    ->
	          let sigma =  !evdref in
		  let c = mkApp (f,Array.map (whd_evar sigma) args) in
	          let t = Retyping.get_type_of env sigma c in
		  make_judge c (* use this for keeping evars: resj.uj_val *) t
              | _ -> resj end
	  | _ -> resj in
	inh_conv_coerce_to_tycon loc env evdref resj tycon

    | GLambda(loc,name,bk,c1,c2)      ->
	let (name',dom,rng) = evd_comb1 (split_tycon loc env) evdref tycon in
	let dom_valcon = valcon_of_tycon dom in
	let j = pretype_type dom_valcon env evdref lvar c1 in
	let var = (name,None,j.utj_val) in
	let j' = pretype rng (push_rel var env) evdref lvar c2 in
	  judge_of_abstraction env (orelse_name name name') j j'

    | GProd(loc,name,bk,c1,c2)        ->
	let j = pretype_type empty_valcon env evdref lvar c1 in
	let j' =
	  if name = Anonymous then
	    let j = pretype_type empty_valcon env evdref lvar c2 in
	      { j with utj_val = lift 1 j.utj_val }
	  else
	    let var = (name,j.utj_val) in
	    let env' = push_rel_assum var env in
	      pretype_type empty_valcon env' evdref lvar c2
	in
	let resj =
	  try judge_of_product env name j j'
	  with TypeError _ as e -> Loc.raise loc e in
	  inh_conv_coerce_to_tycon loc env evdref resj tycon

    | GLetIn(loc,name,c1,c2)      ->
	let j =
	  match c1 with
	  | GCast (loc, c, CastConv (DEFAULTcast, t)) ->
	      let tj = pretype_type empty_valcon env evdref lvar t in
		pretype (mk_tycon tj.utj_val) env evdref lvar c
	  | _ -> pretype empty_tycon env evdref lvar c1
	in
	let t = refresh_universes j.uj_type in
	let var = (name,Some j.uj_val,t) in
        let tycon = lift_tycon 1 tycon in
	let j' = pretype tycon (push_rel var env) evdref lvar c2 in
	  { uj_val = mkLetIn (name, j.uj_val, t, j'.uj_val) ;
	    uj_type = subst1 j.uj_val j'.uj_type }

    | GLetTuple (loc,nal,(na,po),c,d) ->
	let cj = pretype empty_tycon env evdref lvar c in
	let (IndType (indf,realargs)) =
	  try find_rectype env !evdref cj.uj_type
	  with Not_found ->
	    let cloc = loc_of_glob_constr c in
	      error_case_not_inductive_loc cloc env !evdref cj
	in
	let cstrs = get_constructors env indf in
	  if Array.length cstrs <> 1 then
            user_err_loc (loc,"",str "Destructing let is only for inductive types with one constructor.");
	  let cs = cstrs.(0) in
	    if List.length nal <> cs.cs_nargs then
              user_err_loc (loc,"", str "Destructing let on this type expects " ++ int cs.cs_nargs ++ str " variables.");
	    let fsign = List.map2 (fun na (_,c,t) -> (na,c,t))
              (List.rev nal) cs.cs_args in
	    let env_f = push_rels fsign env in
	      (* Make dependencies from arity signature impossible *)
	    let arsgn =
	      let arsgn,_ = get_arity env indf in
		if not !allow_anonymous_refs then
		  List.map (fun (_,b,t) -> (Anonymous,b,t)) arsgn
		else arsgn
	    in
	    let psign = (na,None,build_dependent_inductive env indf)::arsgn in
	    let nar = List.length arsgn in
	      (match po with
		 | Some p ->
		     let env_p = push_rels psign env in
		     let pj = pretype_type empty_valcon env_p evdref lvar p in
		     let ccl = nf_evar !evdref pj.utj_val in
		     let psign = make_arity_signature env true indf in (* with names *)
		     let p = it_mkLambda_or_LetIn ccl psign in
		     let inst =
		       (Array.to_list cs.cs_concl_realargs)
		       @[build_dependent_constructor cs] in
		     let lp = lift cs.cs_nargs p in
		     let fty = hnf_lam_applist env !evdref lp inst in
		     let fj = pretype (mk_tycon fty) env_f evdref lvar d in
		     let f = it_mkLambda_or_LetIn fj.uj_val fsign in
		     let v =
		       let ind,_ = dest_ind_family indf in
		       let ci = make_case_info env ind LetStyle in
		       Typing.check_allowed_sort env !evdref ind cj.uj_val p;
		       mkCase (ci, p, cj.uj_val,[|f|]) in
		     { uj_val = v; uj_type = substl (realargs@[cj.uj_val]) ccl }

		 | None ->
		     let tycon = lift_tycon cs.cs_nargs tycon in
		     let fj = pretype tycon env_f evdref lvar d in
		     let f = it_mkLambda_or_LetIn fj.uj_val fsign in
		     let ccl = nf_evar !evdref fj.uj_type in
		     let ccl =
		       if noccur_between 1 cs.cs_nargs ccl then
			 lift (- cs.cs_nargs) ccl
		       else
			 error_cant_find_case_type_loc loc env !evdref
			   cj.uj_val in
		     let ccl = refresh_universes ccl in
		     let p = it_mkLambda_or_LetIn (lift (nar+1) ccl) psign in
		     let v =
		       let ind,_ = dest_ind_family indf in
		       let ci = make_case_info env ind LetStyle in
		       Typing.check_allowed_sort env !evdref ind cj.uj_val p;
		       mkCase (ci, p, cj.uj_val,[|f|])
		     in { uj_val = v; uj_type = ccl })

    | GIf (loc,c,(na,po),b1,b2) ->
	let cj = pretype empty_tycon env evdref lvar c in
	let (IndType (indf,realargs)) =
	  try find_rectype env !evdref cj.uj_type
	  with Not_found ->
	    let cloc = loc_of_glob_constr c in
	      error_case_not_inductive_loc cloc env !evdref cj in
	let cstrs = get_constructors env indf in
	  if Array.length cstrs <> 2 then
            user_err_loc (loc,"",
			  str "If is only for inductive types with two constructors.");

	  let arsgn =
	    let arsgn,_ = get_arity env indf in
	      if not !allow_anonymous_refs then
		(* Make dependencies from arity signature impossible *)
		List.map (fun (_,b,t) -> (Anonymous,b,t)) arsgn
	      else arsgn
	  in
	  let nar = List.length arsgn in
	  let psign = (na,None,build_dependent_inductive env indf)::arsgn in
	  let pred,p = match po with
	    | Some p ->
		let env_p = push_rels psign env in
		let pj = pretype_type empty_valcon env_p evdref lvar p in
		let ccl = nf_evar !evdref pj.utj_val in
		let pred = it_mkLambda_or_LetIn ccl psign in
		let typ = lift (- nar) (beta_applist (pred,[cj.uj_val])) in
	        pred, typ
	    | None ->
		let p = match tycon with
		  | Some (None, ty) -> ty
		  | None | Some _ -> new_type_evar evdref env loc
		in
		  it_mkLambda_or_LetIn (lift (nar+1) p) psign, p in
	  let pred = nf_evar !evdref pred in
	  let p = nf_evar !evdref p in
	  let f cs b =
	    let n = rel_context_length cs.cs_args in
	    let pi = lift n pred in (* liftn n 2 pred ? *)
	    let pi = beta_applist (pi, [build_dependent_constructor cs]) in
	    let csgn =
	      if not !allow_anonymous_refs then
		List.map (fun (_,b,t) -> (Anonymous,b,t)) cs.cs_args
	      else
		List.map
		  (fun (n, b, t) ->
		     match n with
                         Name _ -> (n, b, t)
                       | Anonymous -> (Name (id_of_string "H"), b, t))
		cs.cs_args
	    in
	    let env_c = push_rels csgn env in
	    let bj = pretype (mk_tycon pi) env_c evdref lvar b in
	      it_mkLambda_or_LetIn bj.uj_val cs.cs_args in
	  let b1 = f cstrs.(0) b1 in
	  let b2 = f cstrs.(1) b2 in
	  let v =
	    let ind,_ = dest_ind_family indf in
	    let ci = make_case_info env ind IfStyle in
	    let pred = nf_evar !evdref pred in
	    Typing.check_allowed_sort env !evdref ind cj.uj_val pred;
	    mkCase (ci, pred, cj.uj_val, [|b1;b2|])
	  in
	    { uj_val = v; uj_type = p }

    | GCases (loc,sty,po,tml,eqns) ->
	Cases.compile_cases loc sty
	  ((fun vtyc env evdref -> pretype vtyc env evdref lvar),evdref)
	  tycon env (* loc *) (po,tml,eqns)

    | GCast (loc,c,k) ->
	let cj =
	  match k with
	      CastCoerce ->
		let cj = pretype empty_tycon env evdref lvar c in
		  evd_comb1 (Coercion.inh_coerce_to_base loc env) evdref cj
	    | CastConv (k,t) ->
		let tj = pretype_type empty_valcon env evdref lvar t in
 		let cj = pretype empty_tycon env evdref lvar c in
		let cty = nf_evar !evdref cj.uj_type and tval = nf_evar !evdref tj.utj_val in
		let cj = match k with
		  | VMcast ->
                      if not (occur_existential cty || occur_existential tval) then
		      begin 
			try 
			  ignore (Reduction.vm_conv Reduction.CUMUL env cty tval); cj
			with Reduction.NotConvertible -> 
			  error_actual_type_loc loc env !evdref cj tval 
		      end
                      else user_err_loc (loc,"",str "Cannot check cast with vm: unresolved arguments remain.")
		  | _ -> inh_conv_coerce_to_tycon loc env evdref cj (mk_tycon tval)
		in
		let v = mkCast (cj.uj_val, k, tval) in
		  { uj_val = v; uj_type = tval }
	in inh_conv_coerce_to_tycon loc env evdref cj tycon

  (* [pretype_type valcon env evdref lvar c] coerces [c] into a type *)
  and pretype_type valcon env evdref lvar = function
    | GHole loc ->
	(match valcon with
	   | Some v ->
               let s =
		 let sigma =  !evdref in
		 let t = Retyping.get_type_of env sigma v in
		   match kind_of_term (whd_betadeltaiota env sigma t) with
                     | Sort s -> s
                     | Evar ev when is_Type (existential_type sigma ev) ->
			 evd_comb1 (define_evar_as_sort) evdref ev
                     | _ -> anomaly "Found a type constraint which is not a type"
               in
		 { utj_val = v;
		   utj_type = s }
	   | None ->
	       let s = evd_comb0 new_sort_variable evdref in
		 { utj_val = e_new_evar evdref env ~src:loc (mkSort s);
		   utj_type = s})
    | c ->
	let j = pretype empty_tycon env evdref lvar c in
	let loc = loc_of_glob_constr c in
	let tj = evd_comb1 (Coercion.inh_coerce_to_sort loc env) evdref j in
	  match valcon with
	    | None -> tj
	    | Some v ->
		if e_cumul env evdref v tj.utj_val then tj
		else
		  error_unexpected_type_loc
                    (loc_of_glob_constr c) env !evdref tj.utj_val v

  let pretype_gen expand_evar fail_evar resolve_classes evdref env lvar kind c =
    let c' = match kind with
      | OfType exptyp ->
	  let tycon = match exptyp with None -> empty_tycon | Some t -> mk_tycon t in
	  (pretype tycon env evdref lvar c).uj_val
      | IsType ->
	  (pretype_type empty_valcon env evdref lvar c).utj_val 
    in
      resolve_evars env evdref fail_evar resolve_classes;
      let c = if expand_evar then nf_evar !evdref c' else c' in
	if fail_evar then check_evars env Evd.empty !evdref c;
	c

  (* TODO: comment faire remonter l'information si le typage a resolu des
     variables du sigma original. il faudrait que la fonction de typage
     retourne aussi le nouveau sigma...
  *)

  let understand_judgment sigma env c =
    let evdref = ref sigma in
    let j = pretype empty_tycon env evdref ([],[]) c in
      resolve_evars env evdref true true;
      let j = j_nf_evar !evdref j in
	check_evars env sigma !evdref (mkCast(j.uj_val,DEFAULTcast, j.uj_type));
	j

  let understand_judgment_tcc evdref env c =
    let j = pretype empty_tycon env evdref ([],[]) c in
      resolve_evars env evdref false true;
      j_nf_evar !evdref j

  (* Raw calls to the unsafe inference machine: boolean says if we must
     fail on unresolved evars; the unsafe_judgment list allows us to
     extend env with some bindings *)

  let ise_pretype_gen expand_evar fail_evar resolve_classes sigma env lvar kind c =
    let evdref = ref sigma in
    let c = pretype_gen expand_evar fail_evar resolve_classes evdref env lvar kind c in
    !evdref, c

  (** Entry points of the high-level type synthesis algorithm *)

  let understand_gen kind sigma env c =
    snd (ise_pretype_gen true true true sigma env ([],[]) kind c)

  let understand sigma env ?expected_type:exptyp c =
    snd (ise_pretype_gen true true true sigma env ([],[]) (OfType exptyp) c)

  let understand_type sigma env c =
    snd (ise_pretype_gen true true true sigma env ([],[]) IsType c)

  let understand_ltac ?(resolve_classes=false) expand_evar sigma env lvar kind c =
    ise_pretype_gen expand_evar false resolve_classes sigma env lvar kind c

  let understand_tcc ?(resolve_classes=true) sigma env ?expected_type:exptyp c =
    ise_pretype_gen true false resolve_classes sigma env ([],[]) (OfType exptyp) c

  let understand_tcc_evars ?(fail_evar=false) ?(resolve_classes=true) evdref env kind c =
    pretype_gen true fail_evar resolve_classes evdref env ([],[]) kind c
end

module Default : S = Pretyping_F(Coercion.Default)