1 files changed, 409 insertions, 384 deletions

diff --git a/compiler/Substitute.ml b/compiler/Substitute.ml
index 38850243..e28f005d 100644
--- a/compiler/Substitute.ml
+++ b/compiler/Substitute.ml
@@ -2,502 +2,527 @@
     function bodies, etc.
  *)
 
-module T = Types
-module TU = TypesUtils
-module V = Values
-module E = Expressions
-module A = LlbcAst
-module C = Contexts
-
-(** Substitute types variables and regions in a type. *)
-let ty_substitute (rsubst : 'r1 -> 'r2) (tsubst : T.TypeVarId.id -> 'r2 T.ty)
-    (cgsubst : T.ConstGenericVarId.id -> T.const_generic) (ty : 'r1 T.ty) :
-    'r2 T.ty =
-  let open T in
-  let visitor =
-    object
-      inherit [_] map_ty
-      method visit_'r _ r = rsubst r
-      method! visit_TypeVar _ id = tsubst id
-
-      method! visit_type_var_id _ _ =
-        (* We should never get here because we reimplemented [visit_TypeVar] *)
-        raise (Failure "Unexpected")
+open Types
+open TypesUtils
+open Values
+open Expressions
+open LlbcAst
+open Contexts
+
+type subst = {
+  r_subst : region -> region;
+      (** Remark: this might be called with bound regions with a negative
+          DeBruijn index. A negative DeBruijn index means that the region
+          is locally bound. *)
+  ty_subst : TypeVarId.id -> ty;
+  cg_subst : ConstGenericVarId.id -> const_generic;
+      (** Substitution from *local* trait clause to trait instance *)
+  tr_subst : TraitClauseId.id -> trait_instance_id;
+      (** Substitution for the [Self] trait instance *)
+  tr_self : trait_instance_id;
+}
+
+let empty_subst : subst =
+  {
+    r_subst = (fun x -> x);
+    ty_subst = (fun id -> TVar id);
+    cg_subst = (fun id -> CgVar id);
+    tr_subst = (fun id -> Clause id);
+    tr_self = Self;
+  }
+
+let st_substitute_visitor (subst : subst) =
+  object (self)
+    inherit [_] map_statement
+    method! visit_region (subst : subst) r = subst.r_subst r
+
+    (** We need to properly handle the DeBruijn indices *)
+    method! visit_TArrow subst regions inputs output =
+      (* Decrement the DeBruijn indices before calling the substitution *)
+      let r_subst r =
+        match r with
+        | RBVar (db, rid) -> subst.r_subst (RBVar (db - 1, rid))
+        | _ -> subst.r_subst r
+      in
+      let subst = { subst with r_subst } in
+      (* Note that we ignore the bound regions variables *)
+      let inputs = List.map (self#visit_ty subst) inputs in
+      let output = self#visit_ty subst output in
+      TArrow (regions, inputs, output)
+
+    method! visit_TVar (subst : subst) id = subst.ty_subst id
+
+    method! visit_type_var_id _ _ =
+      (* We should never get here because we reimplemented [visit_TypeVar] *)
+      raise (Failure "Unexpected")
 
-      method! visit_ConstGenericVar _ id = cgsubst id
+    method! visit_CgVar _ id = subst.cg_subst id
 
-      method! visit_const_generic_var_id _ _ =
-        (* We should never get here because we reimplemented [visit_Var] *)
-        raise (Failure "Unexpected")
-    end
-  in
+    method! visit_const_generic_var_id _ _ =
+      (* We should never get here because we reimplemented [visit_Var] *)
+      raise (Failure "Unexpected")
 
-  visitor#visit_ty () ty
+    method! visit_Clause (subst : subst) id = subst.tr_subst id
+    method! visit_Self (subst : subst) = subst.tr_self
+  end
 
-let rty_substitute (rsubst : T.RegionId.id -> T.RegionId.id)
-    (tsubst : T.TypeVarId.id -> T.rty)
-    (cgsubst : T.ConstGenericVarId.id -> T.const_generic) (ty : T.rty) : T.rty =
-  let rsubst r =
-    match r with T.Static -> T.Static | T.Var rid -> T.Var (rsubst rid)
-  in
-  ty_substitute rsubst tsubst cgsubst ty
+(** Substitute types variables and regions in a type.
 
-let ety_substitute (tsubst : T.TypeVarId.id -> T.ety)
-    (cgsubst : T.ConstGenericVarId.id -> T.const_generic) (ty : T.ety) : T.ety =
-  let rsubst r = r in
-  ty_substitute rsubst tsubst cgsubst ty
+    **IMPORTANT**: this doesn't normalize the types.
+ *)
+let ty_substitute (subst : subst) (ty : ty) : ty =
+  let visitor = st_substitute_visitor subst in
+  visitor#visit_ty subst ty
+
+(** **IMPORTANT**: this doesn't normalize the types. *)
+let trait_ref_substitute (subst : subst) (tr : trait_ref) : trait_ref =
+  let visitor = st_substitute_visitor subst in
+  visitor#visit_trait_ref subst tr
+
+(** **IMPORTANT**: this doesn't normalize the types. *)
+let trait_instance_id_substitute (subst : subst) (tr : trait_instance_id) :
+    trait_instance_id =
+  let visitor = st_substitute_visitor subst in
+  visitor#visit_trait_instance_id subst tr
+
+(** **IMPORTANT**: this doesn't normalize the types. *)
+let generic_args_substitute (subst : subst) (g : generic_args) : generic_args =
+  let visitor = st_substitute_visitor subst in
+  visitor#visit_generic_args subst g
+
+let predicates_substitute (subst : subst) (p : predicates) : predicates =
+  let visitor = st_substitute_visitor subst in
+  visitor#visit_predicates subst p
+
+let erase_regions_subst : subst =
+  {
+    r_subst = (fun _ -> RErased);
+    ty_subst = (fun vid -> TVar vid);
+    cg_subst = (fun id -> CgVar id);
+    tr_subst = (fun id -> Clause id);
+    tr_self = Self;
+  }
+
+(** Erase the region variables in a type *)
+let erase_regions (ty : ty) : ty = ty_substitute erase_regions_subst ty
+
+let trait_ref_erase_regions (tr : trait_ref) : trait_ref =
+  trait_ref_substitute erase_regions_subst tr
+
+let trait_instance_id_erase_regions (tr : trait_instance_id) : trait_instance_id
+    =
+  trait_instance_id_substitute erase_regions_subst tr
 
-(** Convert an {!T.rty} to an {!T.ety} by erasing the region variables *)
-let erase_regions (ty : T.rty) : T.ety =
-  ty_substitute
-    (fun _ -> T.Erased)
-    (fun vid -> T.TypeVar vid)
-    (fun id -> T.ConstGenericVar id)
-    ty
+let generic_args_erase_regions (tr : generic_args) : generic_args =
+  generic_args_substitute erase_regions_subst tr
 
 (** Generate fresh regions for region variables.
 
     Return the list of new regions and appropriate substitutions from the
     original region variables to the fresh regions.
     
-    TODO: simplify? we only need the subst [T.RegionVarId.id -> T.RegionId.id]
+    TODO: simplify? we only need the subst [RegionVarId.id -> RegionId.id]
   *)
-let fresh_regions_with_substs (region_vars : T.region_var list) :
-    T.RegionId.id list
-    * (T.RegionVarId.id -> T.RegionId.id)
-    * (T.RegionVarId.id T.region -> T.RegionId.id T.region) =
+let fresh_regions_with_substs ~(fail_if_not_found : bool)
+    (region_vars : RegionVarId.id list) :
+    RegionId.id list
+    * (RegionVarId.id -> RegionId.id option)
+    * (region -> region) =
   (* Generate fresh regions *)
-  let fresh_region_ids = List.map (fun _ -> C.fresh_region_id ()) region_vars in
+  let fresh_region_ids = List.map (fun _ -> fresh_region_id ()) region_vars in
   (* Generate the map from region var ids to regions *)
   let ls = List.combine region_vars fresh_region_ids in
-  let rid_map =
-    List.fold_left
-      (fun mp ((k : T.region_var), v) -> T.RegionVarId.Map.add k.T.index v mp)
-      T.RegionVarId.Map.empty ls
-  in
+  let rid_map = RegionVarId.Map.of_list ls in
   (* Generate the substitution from region var id to region *)
-  let rid_subst id = T.RegionVarId.Map.find id rid_map in
+  let rid_subst id = RegionVarId.Map.find_opt id rid_map in
   (* Generate the substitution from region to region *)
-  let rsubst r =
-    match r with T.Static -> T.Static | T.Var id -> T.Var (rid_subst id)
+  let r_subst (r : region) =
+    match r with
+    | RStatic | RErased | RFVar _ -> r
+    | RBVar (bdid, id) ->
+        if bdid = 0 then
+          match rid_subst id with
+          | None -> if fail_if_not_found then raise Not_found else r
+          | Some r -> RFVar r
+        else r
   in
   (* Return *)
-  (fresh_region_ids, rid_subst, rsubst)
-
-(** Erase the regions in a type and substitute the type variables *)
-let erase_regions_substitute_types (tsubst : T.TypeVarId.id -> T.ety)
-    (cgsubst : T.ConstGenericVarId.id -> T.const_generic)
-    (ty : 'r T.region T.ty) : T.ety =
-  let rsubst (_ : 'r T.region) : T.erased_region = T.Erased in
-  ty_substitute rsubst tsubst cgsubst ty
+  (fresh_region_ids, rid_subst, r_subst)
+
+let fresh_regions_with_substs_from_vars ~(fail_if_not_found : bool)
+    (region_vars : region_var list) :
+    RegionId.id list
+    * (RegionVarId.id -> RegionId.id option)
+    * (region -> region) =
+  fresh_regions_with_substs ~fail_if_not_found
+    (List.map (fun (r : region_var) -> r.index) region_vars)
+
+(** Erase the regions in a type and perform a substitution *)
+let erase_regions_substitute_types (ty_subst : TypeVarId.id -> ty)
+    (cg_subst : ConstGenericVarId.id -> const_generic)
+    (tr_subst : TraitClauseId.id -> trait_instance_id)
+    (tr_self : trait_instance_id) (ty : ty) : ty =
+  let r_subst (_ : region) : region = RErased in
+  let subst = { r_subst; ty_subst; cg_subst; tr_subst; tr_self } in
+  ty_substitute subst ty
 
 (** Create a region substitution from a list of region variable ids and a list of
     regions (with which to substitute the region variable ids *)
-let make_region_subst (var_ids : T.RegionVarId.id list)
-    (regions : 'r T.region list) : T.RegionVarId.id T.region -> 'r T.region =
+let make_region_subst (var_ids : RegionVarId.id list) (regions : region list) :
+    region -> region =
   let ls = List.combine var_ids regions in
   let mp =
     List.fold_left
-      (fun mp (k, v) -> T.RegionVarId.Map.add k v mp)
-      T.RegionVarId.Map.empty ls
+      (fun mp (k, v) -> RegionVarId.Map.add k v mp)
+      RegionVarId.Map.empty ls
   in
   fun r ->
     match r with
-    | T.Static -> T.Static
-    | T.Var id -> T.RegionVarId.Map.find id mp
+    | RStatic | RErased -> r
+    | RFVar _ -> raise (Failure "Unexpected")
+    | RBVar (bdid, id) ->
+        (* Only substitute the bound regions with DeBruijn index equal to 0 *)
+        if bdid = 0 then RegionVarId.Map.find id mp else r
 
-let make_region_subst_from_vars (vars : T.region_var list)
-    (regions : 'r T.region list) : T.RegionVarId.id T.region -> 'r T.region =
-  make_region_subst
-    (List.map (fun (x : T.region_var) -> x.T.index) vars)
-    regions
+let make_region_subst_from_vars (vars : region_var list) (regions : region list)
+    : region -> region =
+  make_region_subst (List.map (fun (x : region_var) -> x.index) vars) regions
 
 (** Create a type substitution from a list of type variable ids and a list of
     types (with which to substitute the type variable ids) *)
-let make_type_subst (var_ids : T.TypeVarId.id list) (tys : 'r T.ty list) :
-    T.TypeVarId.id -> 'r T.ty =
+let make_type_subst (var_ids : TypeVarId.id list) (tys : ty list) :
+    TypeVarId.id -> ty =
   let ls = List.combine var_ids tys in
   let mp =
     List.fold_left
-      (fun mp (k, v) -> T.TypeVarId.Map.add k v mp)
-      T.TypeVarId.Map.empty ls
+      (fun mp (k, v) -> TypeVarId.Map.add k v mp)
+      TypeVarId.Map.empty ls
   in
-  fun id -> T.TypeVarId.Map.find id mp
+  fun id -> TypeVarId.Map.find id mp
 
-let make_type_subst_from_vars (vars : T.type_var list) (tys : 'r T.ty list) :
-    T.TypeVarId.id -> 'r T.ty =
-  make_type_subst (List.map (fun (x : T.type_var) -> x.T.index) vars) tys
+let make_type_subst_from_vars (vars : type_var list) (tys : ty list) :
+    TypeVarId.id -> ty =
+  make_type_subst (List.map (fun (x : type_var) -> x.index) vars) tys
 
 (** Create a const generic substitution from a list of const generic variable ids and a list of
     const generics (with which to substitute the const generic variable ids) *)
-let make_const_generic_subst (var_ids : T.ConstGenericVarId.id list)
-    (cgs : T.const_generic list) : T.ConstGenericVarId.id -> T.const_generic =
+let make_const_generic_subst (var_ids : ConstGenericVarId.id list)
+    (cgs : const_generic list) : ConstGenericVarId.id -> const_generic =
   let ls = List.combine var_ids cgs in
   let mp =
     List.fold_left
-      (fun mp (k, v) -> T.ConstGenericVarId.Map.add k v mp)
-      T.ConstGenericVarId.Map.empty ls
+      (fun mp (k, v) -> ConstGenericVarId.Map.add k v mp)
+      ConstGenericVarId.Map.empty ls
   in
-  fun id -> T.ConstGenericVarId.Map.find id mp
+  fun id -> ConstGenericVarId.Map.find id mp
 
-let make_const_generic_subst_from_vars (vars : T.const_generic_var list)
-    (cgs : T.const_generic list) : T.ConstGenericVarId.id -> T.const_generic =
+let make_const_generic_subst_from_vars (vars : const_generic_var list)
+    (cgs : const_generic list) : ConstGenericVarId.id -> const_generic =
   make_const_generic_subst
-    (List.map (fun (x : T.const_generic_var) -> x.T.index) vars)
+    (List.map (fun (x : const_generic_var) -> x.index) vars)
     cgs
 
-(** Instantiate the type variables in an ADT definition, and return, for
-    every variant, the list of the types of its fields *)
-let type_decl_get_instantiated_variants_fields_rtypes (def : T.type_decl)
-    (regions : T.RegionId.id T.region list) (types : T.rty list)
-    (cgs : T.const_generic list) : (T.VariantId.id option * T.rty list) list =
-  let r_subst = make_region_subst_from_vars def.T.region_params regions in
-  let ty_subst = make_type_subst_from_vars def.T.type_params types in
+(** Create a trait substitution from a list of trait clause ids and a list of
+    trait refs *)
+let make_trait_subst (clause_ids : TraitClauseId.id list) (trs : trait_ref list)
+    : TraitClauseId.id -> trait_instance_id =
+  let ls = List.combine clause_ids trs in
+  let mp =
+    List.fold_left
+      (fun mp (k, v) -> TraitClauseId.Map.add k (TraitRef v) mp)
+      TraitClauseId.Map.empty ls
+  in
+  fun id -> TraitClauseId.Map.find id mp
+
+let make_trait_subst_from_clauses (clauses : trait_clause list)
+    (trs : trait_ref list) : TraitClauseId.id -> trait_instance_id =
+  make_trait_subst
+    (List.map (fun (x : trait_clause) -> x.clause_id) clauses)
+    trs
+
+let make_subst_from_generics (params : generic_params) (args : generic_args)
+    (tr_self : trait_instance_id) : subst =
+  let r_subst = make_region_subst_from_vars params.regions args.regions in
+  let ty_subst = make_type_subst_from_vars params.types args.types in
   let cg_subst =
-    make_const_generic_subst_from_vars def.T.const_generic_params cgs
+    make_const_generic_subst_from_vars params.const_generics args.const_generics
   in
-  let (variants_fields : (T.VariantId.id option * T.field list) list) =
-    match def.T.kind with
-    | T.Enum variants ->
-        List.mapi
-          (fun i v -> (Some (T.VariantId.of_int i), v.T.fields))
-          variants
-    | T.Struct fields -> [ (None, fields) ]
-    | T.Opaque ->
+  let tr_subst =
+    make_trait_subst_from_clauses params.trait_clauses args.trait_refs
+  in
+  { r_subst; ty_subst; cg_subst; tr_subst; tr_self }
+
+let make_subst_from_generics_erase_regions (params : generic_params)
+    (generics : generic_args) (tr_self : trait_instance_id) =
+  let generics = generic_args_erase_regions generics in
+  let tr_self = trait_instance_id_erase_regions tr_self in
+  let subst = make_subst_from_generics params generics tr_self in
+  { subst with r_subst = (fun _ -> RErased) }
+
+(** Instantiate the type variables in an ADT definition, and return, for
+    every variant, the list of the types of its fields.
+
+    **IMPORTANT**: this function doesn't normalize the types, you may want to
+    use the [AssociatedTypes] equivalent instead.
+*)
+let type_decl_get_instantiated_variants_fields_types (def : type_decl)
+    (generics : generic_args) : (VariantId.id option * ty list) list =
+  (* There shouldn't be any reference to Self *)
+  let tr_self = UnknownTrait __FUNCTION__ in
+  let subst = make_subst_from_generics def.generics generics tr_self in
+  let (variants_fields : (VariantId.id option * field list) list) =
+    match def.kind with
+    | Enum variants ->
+        List.mapi (fun i v -> (Some (VariantId.of_int i), v.fields)) variants
+    | Struct fields -> [ (None, fields) ]
+    | Opaque ->
         raise
           (Failure
              ("Can't retrieve the variants of an opaque type: "
-             ^ Names.name_to_string def.name))
+            ^ show_name def.name))
   in
   List.map
     (fun (id, fields) ->
-      ( id,
-        List.map
-          (fun f -> ty_substitute r_subst ty_subst cg_subst f.T.field_ty)
-          fields ))
+      (id, List.map (fun f -> ty_substitute subst f.field_ty) fields))
     variants_fields
 
 (** Instantiate the type variables in an ADT definition, and return the list
-    of types of the fields for the chosen variant *)
-let type_decl_get_instantiated_field_rtypes (def : T.type_decl)
-    (opt_variant_id : T.VariantId.id option)
-    (regions : T.RegionId.id T.region list) (types : T.rty list)
-    (cgs : T.const_generic list) : T.rty list =
-  let r_subst = make_region_subst_from_vars def.T.region_params regions in
-  let ty_subst = make_type_subst_from_vars def.T.type_params types in
-  let cg_subst =
-    make_const_generic_subst_from_vars def.T.const_generic_params cgs
-  in
-  let fields = TU.type_decl_get_fields def opt_variant_id in
-  List.map
-    (fun f -> ty_substitute r_subst ty_subst cg_subst f.T.field_ty)
-    fields
+    of types of the fields for the chosen variant.
+
+    **IMPORTANT**: this function doesn't normalize the types, you may want to
+    use the [AssociatedTypes] equivalent instead.
+*)
+let type_decl_get_instantiated_field_types (def : type_decl)
+    (opt_variant_id : VariantId.id option) (generics : generic_args) : ty list =
+  (* For now, check that there are no clauses - otherwise we might need
+     to normalize the types *)
+  assert (def.generics.trait_clauses = []);
+  (* There shouldn't be any reference to Self *)
+  let tr_self = UnknownTrait __FUNCTION__ in
+  let subst = make_subst_from_generics def.generics generics tr_self in
+  let fields = type_decl_get_fields def opt_variant_id in
+  List.map (fun f -> ty_substitute subst f.field_ty) fields
 
 (** Return the types of the properly instantiated ADT's variant, provided a
-    context *)
-let ctx_adt_get_instantiated_field_rtypes (ctx : C.eval_ctx)
-    (def_id : T.TypeDeclId.id) (opt_variant_id : T.VariantId.id option)
-    (regions : T.RegionId.id T.region list) (types : T.rty list)
-    (cgs : T.const_generic list) : T.rty list =
-  let def = C.ctx_lookup_type_decl ctx def_id in
-  type_decl_get_instantiated_field_rtypes def opt_variant_id regions types cgs
+    context.
+
+    **IMPORTANT**: this function doesn't normalize the types, you may want to
+    use the [AssociatedTypes] equivalent instead.
+*)
+let ctx_adt_get_instantiated_field_types (ctx : eval_ctx)
+    (def_id : TypeDeclId.id) (opt_variant_id : VariantId.id option)
+    (generics : generic_args) : ty list =
+  let def = ctx_lookup_type_decl ctx def_id in
+  type_decl_get_instantiated_field_types def opt_variant_id generics
 
 (** Return the types of the properly instantiated ADT value (note that
-    here, ADT is understood in its broad meaning: ADT, assumed value or tuple) *)
-let ctx_adt_value_get_instantiated_field_rtypes (ctx : C.eval_ctx)
-    (adt : V.adt_value) (id : T.type_id)
-    (region_params : T.RegionId.id T.region list) (type_params : T.rty list)
-    (cg_params : T.const_generic list) : T.rty list =
+    here, ADT is understood in its broad meaning: ADT, assumed value or tuple).
+
+    **IMPORTANT**: this function doesn't normalize the types, you may want to
+    use the [AssociatedTypes] equivalent instead.
+ *)
+let ctx_adt_value_get_instantiated_field_types (ctx : eval_ctx)
+    (adt : adt_value) (id : type_id) (generics : generic_args) : ty list =
   match id with
-  | T.AdtId id ->
+  | TAdtId id ->
       (* Retrieve the types of the fields *)
-      ctx_adt_get_instantiated_field_rtypes ctx id adt.V.variant_id
-        region_params type_params cg_params
-  | T.Tuple ->
-      assert (List.length region_params = 0);
-      type_params
-  | T.Assumed aty -> (
+      ctx_adt_get_instantiated_field_types ctx id adt.variant_id generics
+  | TTuple ->
+      assert (generics.regions = []);
+      generics.types
+  | TAssumed aty -> (
       match aty with
-      | T.Box | T.Vec ->
-          assert (List.length region_params = 0);
-          assert (List.length type_params = 1);
-          assert (List.length cg_params = 0);
-          type_params
-      | T.Option ->
-          assert (List.length region_params = 0);
-          assert (List.length type_params = 1);
-          assert (List.length cg_params = 0);
-          if adt.V.variant_id = Some T.option_some_id then type_params
-          else if adt.V.variant_id = Some T.option_none_id then []
-          else raise (Failure "Unreachable")
-      | T.Range ->
-          assert (List.length region_params = 0);
-          assert (List.length type_params = 1);
-          assert (List.length cg_params = 0);
-          type_params
-      | T.Array | T.Slice | T.Str ->
+      | TBox ->
+          assert (generics.regions = []);
+          assert (List.length generics.types = 1);
+          assert (generics.const_generics = []);
+          generics.types
+      | TArray | TSlice | TStr ->
           (* Those types don't have fields *)
           raise (Failure "Unreachable"))
 
-(** Instantiate the type variables in an ADT definition, and return the list
-    of types of the fields for the chosen variant *)
-let type_decl_get_instantiated_field_etypes (def : T.type_decl)
-    (opt_variant_id : T.VariantId.id option) (types : T.ety list)
-    (cgs : T.const_generic list) : T.ety list =
-  let ty_subst = make_type_subst_from_vars def.T.type_params types in
-  let cg_subst =
-    make_const_generic_subst_from_vars def.T.const_generic_params cgs
-  in
-  let fields = TU.type_decl_get_fields def opt_variant_id in
-  List.map
-    (fun f -> erase_regions_substitute_types ty_subst cg_subst f.T.field_ty)
-    fields
-
-(** Return the types of the properly instantiated ADT's variant, provided a
-    context *)
-let ctx_adt_get_instantiated_field_etypes (ctx : C.eval_ctx)
-    (def_id : T.TypeDeclId.id) (opt_variant_id : T.VariantId.id option)
-    (types : T.ety list) (cgs : T.const_generic list) : T.ety list =
-  let def = C.ctx_lookup_type_decl ctx def_id in
-  type_decl_get_instantiated_field_etypes def opt_variant_id types cgs
-
-let statement_substitute_visitor (tsubst : T.TypeVarId.id -> T.ety)
-    (cgsubst : T.ConstGenericVarId.id -> T.const_generic) =
-  object
-    inherit [_] A.map_statement
-    method! visit_ety _ ty = ety_substitute tsubst cgsubst ty
-    method! visit_ConstGenericVar _ id = cgsubst id
-
-    method! visit_const_generic_var_id _ _ =
-      (* We should never get here because we reimplemented [visit_Var] *)
-      raise (Failure "Unexpected")
-  end
-
 (** Apply a type substitution to a place *)
-let place_substitute (tsubst : T.TypeVarId.id -> T.ety)
-    (cgsubst : T.ConstGenericVarId.id -> T.const_generic) (p : E.place) :
-    E.place =
+let place_substitute (subst : subst) (p : place) : place =
   (* There is in fact nothing to do *)
-  (statement_substitute_visitor tsubst cgsubst)#visit_place () p
+  (st_substitute_visitor subst)#visit_place subst p
 
 (** Apply a type substitution to an operand *)
-let operand_substitute (tsubst : T.TypeVarId.id -> T.ety)
-    (cgsubst : T.ConstGenericVarId.id -> T.const_generic) (op : E.operand) :
-    E.operand =
-  (statement_substitute_visitor tsubst cgsubst)#visit_operand () op
+let operand_substitute (subst : subst) (op : operand) : operand =
+  (st_substitute_visitor subst)#visit_operand subst op
 
 (** Apply a type substitution to an rvalue *)
-let rvalue_substitute (tsubst : T.TypeVarId.id -> T.ety)
-    (cgsubst : T.ConstGenericVarId.id -> T.const_generic) (rv : E.rvalue) :
-    E.rvalue =
-  (statement_substitute_visitor tsubst cgsubst)#visit_rvalue () rv
+let rvalue_substitute (subst : subst) (rv : rvalue) : rvalue =
+  (st_substitute_visitor subst)#visit_rvalue subst rv
 
 (** Apply a type substitution to an assertion *)
-let assertion_substitute (tsubst : T.TypeVarId.id -> T.ety)
-    (cgsubst : T.ConstGenericVarId.id -> T.const_generic) (a : A.assertion) :
-    A.assertion =
-  (statement_substitute_visitor tsubst cgsubst)#visit_assertion () a
+let assertion_substitute (subst : subst) (a : assertion) : assertion =
+  (st_substitute_visitor subst)#visit_assertion subst a
 
 (** Apply a type substitution to a call *)
-let call_substitute (tsubst : T.TypeVarId.id -> T.ety)
-    (cgsubst : T.ConstGenericVarId.id -> T.const_generic) (call : A.call) :
-    A.call =
-  (statement_substitute_visitor tsubst cgsubst)#visit_call () call
+let call_substitute (subst : subst) (call : call) : call =
+  (st_substitute_visitor subst)#visit_call subst call
 
 (** Apply a type substitution to a statement *)
-let statement_substitute (tsubst : T.TypeVarId.id -> T.ety)
-    (cgsubst : T.ConstGenericVarId.id -> T.const_generic) (st : A.statement) :
-    A.statement =
-  (statement_substitute_visitor tsubst cgsubst)#visit_statement () st
+let statement_substitute (subst : subst) (st : statement) : statement =
+  (st_substitute_visitor subst)#visit_statement subst st
 
 (** Apply a type substitution to a function body. Return the local variables
     and the body. *)
-let fun_body_substitute_in_body (tsubst : T.TypeVarId.id -> T.ety)
-    (cgsubst : T.ConstGenericVarId.id -> T.const_generic) (body : A.fun_body) :
-    A.var list * A.statement =
-  let rsubst r = r in
+let fun_body_substitute_in_body (subst : subst) (body : fun_body) :
+    var list * statement =
   let locals =
     List.map
-      (fun (v : A.var) ->
-        { v with A.var_ty = ty_substitute rsubst tsubst cgsubst v.A.var_ty })
-      body.A.locals
+      (fun (v : var) -> { v with var_ty = ty_substitute subst v.var_ty })
+      body.locals
   in
-  let body = statement_substitute tsubst cgsubst body.body in
+  let body = statement_substitute subst body.body in
   (locals, body)
 
-(** Substitute a function signature *)
-let substitute_signature (asubst : T.RegionGroupId.id -> V.AbstractionId.id)
-    (rsubst : T.RegionVarId.id -> T.RegionId.id)
-    (tsubst : T.TypeVarId.id -> T.rty)
-    (cgsubst : T.ConstGenericVarId.id -> T.const_generic) (sg : A.fun_sig) :
-    A.inst_fun_sig =
-  let rsubst' (r : T.RegionVarId.id T.region) : T.RegionId.id T.region =
-    match r with T.Static -> T.Static | T.Var rid -> T.Var (rsubst rid)
+let trait_type_constraint_substitute (subst : subst)
+    (ttc : trait_type_constraint) : trait_type_constraint =
+  let { trait_ref; generics; type_name; ty } = ttc in
+  let visitor = st_substitute_visitor subst in
+  let trait_ref = visitor#visit_trait_ref subst trait_ref in
+  let generics = visitor#visit_generic_args subst generics in
+  let ty = visitor#visit_ty subst ty in
+  { trait_ref; generics; type_name; ty }
+
+(** Substitute a function signature, together with the regions hierarchy
+    associated to that signature.
+
+    **IMPORTANT:** this function doesn't normalize the types.
+ *)
+let substitute_signature (asubst : RegionGroupId.id -> AbstractionId.id)
+    (r_subst : RegionVarId.id -> RegionId.id) (ty_subst : TypeVarId.id -> ty)
+    (cg_subst : ConstGenericVarId.id -> const_generic)
+    (tr_subst : TraitClauseId.id -> trait_instance_id)
+    (tr_self : trait_instance_id) (sg : fun_sig)
+    (regions_hierarchy : region_var_groups) : inst_fun_sig =
+  let r_subst' (r : region) : region =
+    match r with
+    | RStatic | RErased | RFVar _ -> r
+    | RBVar (bdid, rid) -> if bdid = 0 then RFVar (r_subst rid) else r
   in
-  let inputs = List.map (ty_substitute rsubst' tsubst cgsubst) sg.A.inputs in
-  let output = ty_substitute rsubst' tsubst cgsubst sg.A.output in
-  let subst_region_group (rg : T.region_var_group) : A.abs_region_group =
+  let subst = { r_subst = r_subst'; ty_subst; cg_subst; tr_subst; tr_self } in
+  let inputs = List.map (ty_substitute subst) sg.inputs in
+  let output = ty_substitute subst sg.output in
+  let subst_region_group (rg : region_var_group) : abs_region_group =
     let id = asubst rg.id in
-    let regions = List.map rsubst rg.regions in
+    let regions = List.map r_subst rg.regions in
     let parents = List.map asubst rg.parents in
-    { id; regions; parents }
+    ({ id; regions; parents } : abs_region_group)
   in
-  let regions_hierarchy = List.map subst_region_group sg.A.regions_hierarchy in
-  { A.regions_hierarchy; inputs; output }
-
-(** Substitute type variable identifiers in a type *)
-let ty_substitute_ids (tsubst : T.TypeVarId.id -> T.TypeVarId.id)
-    (cgsubst : T.ConstGenericVarId.id -> T.ConstGenericVarId.id) (ty : 'r T.ty)
-    : 'r T.ty =
-  let open T in
+  let regions_hierarchy = List.map subst_region_group regions_hierarchy in
+  let trait_type_constraints =
+    List.map
+      (trait_type_constraint_substitute subst)
+      sg.preds.trait_type_constraints
+  in
+  { inputs; output; regions_hierarchy; trait_type_constraints }
+
+(** Substitute variable identifiers in a type *)
+let statement_substitute_ids (ty_subst : TypeVarId.id -> TypeVarId.id)
+    (cg_subst : ConstGenericVarId.id -> ConstGenericVarId.id) (ty : ty) : ty =
   let visitor =
     object
       inherit [_] map_ty
       method visit_'r _ r = r
-      method! visit_type_var_id _ id = tsubst id
-      method! visit_const_generic_var_id _ id = cgsubst id
+      method! visit_type_var_id _ id = ty_subst id
+      method! visit_const_generic_var_id _ id = cg_subst id
     end
   in
 
   visitor#visit_ty () ty
 
-(* This visitor is a mess...
-
-   We want to write a class which visits abstractions, values, etc. *and their
-   types* to substitute identifiers.
-
-   The issue is that we derive two specialized types (ety and rty) from a
-   polymorphic type (ty). Because of this, there are typing issues with
-   [visit_'r] if we define a class which visits objects of types [ety] and [rty]
-   while inheriting a class which visit [ty]...
-*)
-let subst_ids_visitor (rsubst : T.RegionId.id -> T.RegionId.id)
-    (rvsubst : T.RegionVarId.id -> T.RegionVarId.id)
-    (tsubst : T.TypeVarId.id -> T.TypeVarId.id)
-    (cgsubst : T.ConstGenericVarId.id -> T.ConstGenericVarId.id)
-    (ssubst : V.SymbolicValueId.id -> V.SymbolicValueId.id)
-    (bsubst : V.BorrowId.id -> V.BorrowId.id)
-    (asubst : V.AbstractionId.id -> V.AbstractionId.id) =
-  let subst_rty =
-    object
-      inherit [_] T.map_ty
-
-      method visit_'r _ r =
-        match r with T.Static -> T.Static | T.Var rid -> T.Var (rsubst rid)
-
-      method! visit_type_var_id _ id = tsubst id
-      method! visit_const_generic_var_id _ id = cgsubst id
-    end
-  in
-
-  let visitor =
-    object (self : 'self)
-      inherit [_] C.map_env
-      method! visit_borrow_id _ bid = bsubst bid
-      method! visit_loan_id _ bid = bsubst bid
-      method! visit_ety _ ty = ty_substitute_ids tsubst cgsubst ty
-      method! visit_rty env ty = subst_rty#visit_ty env ty
-      method! visit_symbolic_value_id _ id = ssubst id
-
-      (** We *do* visit meta-values *)
-      method! visit_msymbolic_value env sv = self#visit_symbolic_value env sv
-
-      (** We *do* visit meta-values *)
-      method! visit_mvalue env v = self#visit_typed_value env v
-
-      method! visit_region_id _ id = rsubst id
-      method! visit_region_var_id _ id = rvsubst id
-      method! visit_abstraction_id _ id = asubst id
-    end
-  in
-
-  object
-    method visit_ety (x : T.ety) : T.ety = visitor#visit_ety () x
-    method visit_rty (x : T.rty) : T.rty = visitor#visit_rty () x
-
-    method visit_typed_value (x : V.typed_value) : V.typed_value =
-      visitor#visit_typed_value () x
-
-    method visit_typed_avalue (x : V.typed_avalue) : V.typed_avalue =
-      visitor#visit_typed_avalue () x
-
-    method visit_abs (x : V.abs) : V.abs = visitor#visit_abs () x
-    method visit_env (env : C.env) : C.env = visitor#visit_env () env
+let subst_ids_visitor (r_subst : RegionId.id -> RegionId.id)
+    (ty_subst : TypeVarId.id -> TypeVarId.id)
+    (cg_subst : ConstGenericVarId.id -> ConstGenericVarId.id)
+    (ssubst : SymbolicValueId.id -> SymbolicValueId.id)
+    (bsubst : BorrowId.id -> BorrowId.id)
+    (asubst : AbstractionId.id -> AbstractionId.id) =
+  object (self : 'self)
+    inherit [_] map_env
+    method! visit_type_var_id _ id = ty_subst id
+    method! visit_const_generic_var_id _ id = cg_subst id
+    method! visit_region_id _ rid = r_subst rid
+    method! visit_borrow_id _ bid = bsubst bid
+    method! visit_loan_id _ bid = bsubst bid
+    method! visit_symbolic_value_id _ id = ssubst id
+
+    (** We *do* visit meta-values *)
+    method! visit_msymbolic_value env sv = self#visit_symbolic_value env sv
+
+    (** We *do* visit meta-values *)
+    method! visit_mvalue env v = self#visit_typed_value env v
+
+    method! visit_abstraction_id _ id = asubst id
   end
 
-let typed_value_subst_ids (rsubst : T.RegionId.id -> T.RegionId.id)
-    (rvsubst : T.RegionVarId.id -> T.RegionVarId.id)
-    (tsubst : T.TypeVarId.id -> T.TypeVarId.id)
-    (cgsubst : T.ConstGenericVarId.id -> T.ConstGenericVarId.id)
-    (ssubst : V.SymbolicValueId.id -> V.SymbolicValueId.id)
-    (bsubst : V.BorrowId.id -> V.BorrowId.id) (v : V.typed_value) :
-    V.typed_value =
+let typed_value_subst_ids (r_subst : RegionId.id -> RegionId.id)
+    (ty_subst : TypeVarId.id -> TypeVarId.id)
+    (cg_subst : ConstGenericVarId.id -> ConstGenericVarId.id)
+    (ssubst : SymbolicValueId.id -> SymbolicValueId.id)
+    (bsubst : BorrowId.id -> BorrowId.id) (v : typed_value) : typed_value =
   let asubst _ = raise (Failure "Unreachable") in
-  (subst_ids_visitor rsubst rvsubst tsubst cgsubst ssubst bsubst asubst)
-    #visit_typed_value v
+  let vis = subst_ids_visitor r_subst ty_subst cg_subst ssubst bsubst asubst in
+  vis#visit_typed_value () v
 
-let typed_value_subst_rids (rsubst : T.RegionId.id -> T.RegionId.id)
-    (v : V.typed_value) : V.typed_value =
-  typed_value_subst_ids rsubst
-    (fun x -> x)
+let typed_value_subst_rids (r_subst : RegionId.id -> RegionId.id)
+    (v : typed_value) : typed_value =
+  typed_value_subst_ids r_subst
     (fun x -> x)
     (fun x -> x)
     (fun x -> x)
     (fun x -> x)
     v
 
-let typed_avalue_subst_ids (rsubst : T.RegionId.id -> T.RegionId.id)
-    (rvsubst : T.RegionVarId.id -> T.RegionVarId.id)
-    (tsubst : T.TypeVarId.id -> T.TypeVarId.id)
-    (cgsubst : T.ConstGenericVarId.id -> T.ConstGenericVarId.id)
-    (ssubst : V.SymbolicValueId.id -> V.SymbolicValueId.id)
-    (bsubst : V.BorrowId.id -> V.BorrowId.id) (v : V.typed_avalue) :
-    V.typed_avalue =
+let typed_avalue_subst_ids (r_subst : RegionId.id -> RegionId.id)
+    (ty_subst : TypeVarId.id -> TypeVarId.id)
+    (cg_subst : ConstGenericVarId.id -> ConstGenericVarId.id)
+    (ssubst : SymbolicValueId.id -> SymbolicValueId.id)
+    (bsubst : BorrowId.id -> BorrowId.id) (v : typed_avalue) : typed_avalue =
   let asubst _ = raise (Failure "Unreachable") in
-  (subst_ids_visitor rsubst rvsubst tsubst cgsubst ssubst bsubst asubst)
-    #visit_typed_avalue v
-
-let abs_subst_ids (rsubst : T.RegionId.id -> T.RegionId.id)
-    (rvsubst : T.RegionVarId.id -> T.RegionVarId.id)
-    (tsubst : T.TypeVarId.id -> T.TypeVarId.id)
-    (cgsubst : T.ConstGenericVarId.id -> T.ConstGenericVarId.id)
-    (ssubst : V.SymbolicValueId.id -> V.SymbolicValueId.id)
-    (bsubst : V.BorrowId.id -> V.BorrowId.id)
-    (asubst : V.AbstractionId.id -> V.AbstractionId.id) (x : V.abs) : V.abs =
-  (subst_ids_visitor rsubst rvsubst tsubst cgsubst ssubst bsubst asubst)
-    #visit_abs x
-
-let env_subst_ids (rsubst : T.RegionId.id -> T.RegionId.id)
-    (rvsubst : T.RegionVarId.id -> T.RegionVarId.id)
-    (tsubst : T.TypeVarId.id -> T.TypeVarId.id)
-    (cgsubst : T.ConstGenericVarId.id -> T.ConstGenericVarId.id)
-    (ssubst : V.SymbolicValueId.id -> V.SymbolicValueId.id)
-    (bsubst : V.BorrowId.id -> V.BorrowId.id)
-    (asubst : V.AbstractionId.id -> V.AbstractionId.id) (x : C.env) : C.env =
-  (subst_ids_visitor rsubst rvsubst tsubst cgsubst ssubst bsubst asubst)
-    #visit_env x
-
-let typed_avalue_subst_rids (rsubst : T.RegionId.id -> T.RegionId.id)
-    (x : V.typed_avalue) : V.typed_avalue =
+  let vis = subst_ids_visitor r_subst ty_subst cg_subst ssubst bsubst asubst in
+  vis#visit_typed_avalue () v
+
+let abs_subst_ids (r_subst : RegionId.id -> RegionId.id)
+    (ty_subst : TypeVarId.id -> TypeVarId.id)
+    (cg_subst : ConstGenericVarId.id -> ConstGenericVarId.id)
+    (ssubst : SymbolicValueId.id -> SymbolicValueId.id)
+    (bsubst : BorrowId.id -> BorrowId.id)
+    (asubst : AbstractionId.id -> AbstractionId.id) (x : abs) : abs =
+  let vis = subst_ids_visitor r_subst ty_subst cg_subst ssubst bsubst asubst in
+  vis#visit_abs () x
+
+let env_subst_ids (r_subst : RegionId.id -> RegionId.id)
+    (ty_subst : TypeVarId.id -> TypeVarId.id)
+    (cg_subst : ConstGenericVarId.id -> ConstGenericVarId.id)
+    (ssubst : SymbolicValueId.id -> SymbolicValueId.id)
+    (bsubst : BorrowId.id -> BorrowId.id)
+    (asubst : AbstractionId.id -> AbstractionId.id) (x : env) : env =
+  let vis = subst_ids_visitor r_subst ty_subst cg_subst ssubst bsubst asubst in
+  vis#visit_env () x
+
+let typed_avalue_subst_rids (r_subst : RegionId.id -> RegionId.id)
+    (x : typed_avalue) : typed_avalue =
   let asubst _ = raise (Failure "Unreachable") in
-  (subst_ids_visitor rsubst
-     (fun x -> x)
-     (fun x -> x)
-     (fun x -> x)
-     (fun x -> x)
-     (fun x -> x)
-     asubst)
-    #visit_typed_avalue
-    x
-
-let env_subst_rids (rsubst : T.RegionId.id -> T.RegionId.id) (x : C.env) : C.env
-    =
-  (subst_ids_visitor rsubst
-     (fun x -> x)
-     (fun x -> x)
-     (fun x -> x)
-     (fun x -> x)
-     (fun x -> x)
-     (fun x -> x))
-    #visit_env
-    x
+  let vis =
+    subst_ids_visitor r_subst
+      (fun x -> x)
+      (fun x -> x)
+      (fun x -> x)
+      (fun x -> x)
+      asubst
+  in
+  vis#visit_typed_avalue () x
+
+let env_subst_rids (r_subst : RegionId.id -> RegionId.id) (x : env) : env =
+  let vis =
+    subst_ids_visitor r_subst
+      (fun x -> x)
+      (fun x -> x)
+      (fun x -> x)
+      (fun x -> x)
+      (fun x -> x)
+  in
+  vis#visit_env () x