From b9f33bdd871a1bd7a1bd29f148dd05bd7990548b Mon Sep 17 00:00:00 2001
From: Son Ho
Date: Sun, 12 Nov 2023 19:28:56 +0100
Subject: Remove the 'r type variable from the ty type definition

---
 compiler/Substitute.ml | 426 ++++++++++++++++++-------------------------------
 1 file changed, 152 insertions(+), 274 deletions(-)

(limited to 'compiler/Substitute.ml')

diff --git a/compiler/Substitute.ml b/compiler/Substitute.ml
index 23f618e2..b4eee9f8 100644
--- a/compiler/Substitute.ml
+++ b/compiler/Substitute.ml
@@ -9,20 +9,20 @@ module E = Expressions
 module A = LlbcAst
 module C = Contexts
 
-type ('r1, 'r2) subst = {
-  r_subst : 'r1 -> 'r2;
-  ty_subst : T.TypeVarId.id -> 'r2 T.ty;
+type subst = {
+  r_subst : T.region -> T.region;
+  ty_subst : T.TypeVarId.id -> T.ty;
   cg_subst : T.ConstGenericVarId.id -> T.const_generic;
       (** Substitution from *local* trait clause to trait instance *)
-  tr_subst : T.TraitClauseId.id -> 'r2 T.trait_instance_id;
+  tr_subst : T.TraitClauseId.id -> T.trait_instance_id;
       (** Substitution for the [Self] trait instance *)
-  tr_self : 'r2 T.trait_instance_id;
+  tr_self : T.trait_instance_id;
 }
 
-let ty_substitute_visitor (subst : ('r1, 'r2) subst) =
+let st_substitute_visitor (subst : subst) =
   object
-    inherit [_] T.map_ty
-    method visit_'r _ r = subst.r_subst r
+    inherit [_] A.map_statement
+    method! visit_region _ r = subst.r_subst r
     method! visit_TypeVar _ id = subst.ty_subst id
 
     method! visit_type_var_id _ _ =
@@ -43,25 +43,30 @@ let ty_substitute_visitor (subst : ('r1, 'r2) subst) =
 
     **IMPORTANT**: this doesn't normalize the types.
  *)
-let ty_substitute (subst : ('r1, 'r2) subst) (ty : 'r1 T.ty) : 'r2 T.ty =
-  let visitor = ty_substitute_visitor subst in
+let ty_substitute (subst : subst) (ty : T.ty) : T.ty =
+  let visitor = st_substitute_visitor subst in
   visitor#visit_ty () ty
 
 (** **IMPORTANT**: this doesn't normalize the types. *)
-let trait_ref_substitute (subst : ('r1, 'r2) subst) (tr : 'r1 T.trait_ref) :
-    'r2 T.trait_ref =
-  let visitor = ty_substitute_visitor subst in
+let trait_ref_substitute (subst : subst) (tr : T.trait_ref) : T.trait_ref =
+  let visitor = st_substitute_visitor subst in
   visitor#visit_trait_ref () tr
 
 (** **IMPORTANT**: this doesn't normalize the types. *)
-let generic_args_substitute (subst : ('r1, 'r2) subst) (g : 'r1 T.generic_args)
-    : 'r2 T.generic_args =
-  let visitor = ty_substitute_visitor subst in
+let trait_instance_id_substitute (subst : subst) (tr : T.trait_instance_id) :
+    T.trait_instance_id =
+  let visitor = st_substitute_visitor subst in
+  visitor#visit_trait_instance_id () tr
+
+(** **IMPORTANT**: this doesn't normalize the types. *)
+let generic_args_substitute (subst : subst) (g : T.generic_args) :
+    T.generic_args =
+  let visitor = st_substitute_visitor subst in
   visitor#visit_generic_args () g
 
-let erase_regions_subst : ('r, T.erased_region) subst =
+let erase_regions_subst : subst =
   {
-    r_subst = (fun _ -> T.Erased);
+    r_subst = (fun _ -> T.RErased);
     ty_subst = (fun vid -> T.TypeVar vid);
     cg_subst = (fun id -> T.ConstGenericVar id);
     tr_subst = (fun id -> T.Clause id);
@@ -69,11 +74,18 @@ let erase_regions_subst : ('r, T.erased_region) subst =
   }
 
 (** Convert an {!T.rty} to an {!T.ety} by erasing the region variables *)
-let erase_regions (ty : 'r T.ty) : T.ety = ty_substitute erase_regions_subst ty
+let erase_regions (ty : T.ty) : T.ty = ty_substitute erase_regions_subst ty
 
-let trait_ref_erase_regions (tr : 'r T.trait_ref) : T.etrait_ref =
+let trait_ref_erase_regions (tr : T.trait_ref) : T.trait_ref =
   trait_ref_substitute erase_regions_subst tr
 
+let trait_instance_id_erase_regions (tr : T.trait_instance_id) :
+    T.trait_instance_id =
+  trait_instance_id_substitute erase_regions_subst tr
+
+let generic_args_erase_regions (tr : T.generic_args) : T.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
@@ -83,60 +95,62 @@ let trait_ref_erase_regions (tr : 'r T.trait_ref) : T.etrait_ref =
   *)
 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) =
+    * (T.RegionId.id -> T.RegionId.id)
+    * (T.region -> T.region) =
   (* Generate fresh regions *)
   let fresh_region_ids = List.map (fun _ -> C.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
+      (fun mp ((k : T.region_var), v) -> T.RegionId.Map.add k.T.index v mp)
+      T.RegionId.Map.empty 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 = T.RegionId.Map.find id rid_map in
   (* Generate the substitution from region to region *)
-  let r_subst r =
-    match r with T.Static -> T.Static | T.Var id -> T.Var (rid_subst id)
+  let r_subst (r : T.region) =
+    match r with
+    | T.RStatic | T.RErased -> r
+    | T.RVar id -> T.RVar (rid_subst id)
   in
   (* Return *)
   (fresh_region_ids, rid_subst, r_subst)
 
 (** Erase the regions in a type and perform a substitution *)
-let erase_regions_substitute_types (ty_subst : T.TypeVarId.id -> T.ety)
+let erase_regions_substitute_types (ty_subst : T.TypeVarId.id -> T.ty)
     (cg_subst : T.ConstGenericVarId.id -> T.const_generic)
-    (tr_subst : T.TraitClauseId.id -> T.etrait_instance_id)
-    (tr_self : T.etrait_instance_id) (ty : 'r T.ty) : T.ety =
-  let r_subst (_ : 'r) : T.erased_region = T.Erased in
+    (tr_subst : T.TraitClauseId.id -> T.trait_instance_id)
+    (tr_self : T.trait_instance_id) (ty : T.ty) : T.ty =
+  let r_subst (_ : T.region) : T.region = T.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 : T.RegionId.id list) (regions : T.region list) :
+    T.region -> T.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) -> T.RegionId.Map.add k v mp)
+      T.RegionId.Map.empty ls
   in
   fun r ->
     match r with
-    | T.Static -> T.Static
-    | T.Var id -> T.RegionVarId.Map.find id mp
+    | T.RStatic | T.RErased -> r
+    | T.RVar id -> T.RegionId.Map.find id mp
 
 let make_region_subst_from_vars (vars : T.region_var list)
-    (regions : 'r T.region list) : T.RegionVarId.id T.region -> 'r T.region =
+    (regions : T.region list) : T.region -> T.region =
   make_region_subst
     (List.map (fun (x : T.region_var) -> x.T.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 : T.TypeVarId.id list) (tys : T.ty list) :
+    T.TypeVarId.id -> T.ty =
   let ls = List.combine var_ids tys in
   let mp =
     List.fold_left
@@ -145,8 +159,8 @@ let make_type_subst (var_ids : T.TypeVarId.id list) (tys : 'r T.ty list) :
   in
   fun id -> T.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 =
+let make_type_subst_from_vars (vars : T.type_var list) (tys : T.ty list) :
+    T.TypeVarId.id -> T.ty =
   make_type_subst (List.map (fun (x : T.type_var) -> x.T.index) vars) tys
 
 (** Create a const generic substitution from a list of const generic variable ids and a list of
@@ -170,7 +184,7 @@ let make_const_generic_subst_from_vars (vars : T.const_generic_var list)
 (** Create a trait substitution from a list of trait clause ids and a list of
     trait refs *)
 let make_trait_subst (clause_ids : T.TraitClauseId.id list)
-    (trs : 'r T.trait_ref list) : T.TraitClauseId.id -> 'r T.trait_instance_id =
+    (trs : T.trait_ref list) : T.TraitClauseId.id -> T.trait_instance_id =
   let ls = List.combine clause_ids trs in
   let mp =
     List.fold_left
@@ -180,15 +194,13 @@ let make_trait_subst (clause_ids : T.TraitClauseId.id list)
   fun id -> T.TraitClauseId.Map.find id mp
 
 let make_trait_subst_from_clauses (clauses : T.trait_clause list)
-    (trs : 'r T.trait_ref list) : T.TraitClauseId.id -> 'r T.trait_instance_id =
+    (trs : T.trait_ref list) : T.TraitClauseId.id -> T.trait_instance_id =
   make_trait_subst
     (List.map (fun (x : T.trait_clause) -> x.T.clause_id) clauses)
     trs
 
-let make_subst_from_generics (params : T.generic_params)
-    (args : 'r T.region T.generic_args)
-    (tr_self : 'r T.region T.trait_instance_id) :
-    (T.region_var_id T.region, 'r T.region) subst =
+let make_subst_from_generics (params : T.generic_params) (args : T.generic_args)
+    (tr_self : T.trait_instance_id) : subst =
   let r_subst = make_region_subst_from_vars params.T.regions args.T.regions in
   let ty_subst = make_type_subst_from_vars params.T.types args.T.types in
   let cg_subst =
@@ -200,36 +212,12 @@ let make_subst_from_generics (params : T.generic_params)
   in
   { r_subst; ty_subst; cg_subst; tr_subst; tr_self }
 
-let make_subst_from_generics_no_regions :
-      'r.
-      T.generic_params ->
-      'r T.generic_args ->
-      'r T.trait_instance_id ->
-      (T.region_var_id T.region, 'r) subst =
- fun params args tr_self ->
-  let r_subst _ = raise (Failure "Unexpected region") in
-  let ty_subst = make_type_subst_from_vars params.T.types args.T.types in
-  let cg_subst =
-    make_const_generic_subst_from_vars params.T.const_generics
-      args.T.const_generics
-  in
-  let tr_subst =
-    make_trait_subst_from_clauses params.T.trait_clauses args.T.trait_refs
-  in
-  { r_subst; ty_subst; cg_subst; tr_subst; tr_self }
-
-let make_esubst_from_generics (params : T.generic_params)
-    (generics : T.egeneric_args) (tr_self : T.etrait_instance_id) =
-  let r_subst _ = T.Erased in
-  let ty_subst = make_type_subst_from_vars params.types generics.T.types in
-  let cg_subst =
-    make_const_generic_subst_from_vars params.const_generics
-      generics.T.const_generics
-  in
-  let tr_subst =
-    make_trait_subst_from_clauses params.trait_clauses generics.T.trait_refs
-  in
-  { r_subst; ty_subst; cg_subst; tr_subst; tr_self }
+let make_subst_from_generics_erase_regions (params : T.generic_params)
+    (generics : T.generic_args) (tr_self : T.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 _ -> T.RErased) }
 
 (** Instantiate the type variables in an ADT definition, and return, for
     every variant, the list of the types of its fields.
@@ -237,8 +225,8 @@ let make_esubst_from_generics (params : T.generic_params)
     **IMPORTANT**: this function doesn't normalize the types, you may want to
     use the [AssociatedTypes] equivalent instead.
 *)
-let type_decl_get_instantiated_variants_fields_rtypes (def : T.type_decl)
-    (generics : T.rgeneric_args) : (T.VariantId.id option * T.rty list) list =
+let type_decl_get_instantiated_variants_fields_types (def : T.type_decl)
+    (generics : T.generic_args) : (T.VariantId.id option * T.ty list) list =
   (* There shouldn't be any reference to Self *)
   let tr_self = T.UnknownTrait __FUNCTION__ in
   let subst = make_subst_from_generics def.T.generics generics tr_self in
@@ -266,9 +254,9 @@ let type_decl_get_instantiated_variants_fields_rtypes (def : T.type_decl)
     **IMPORTANT**: this function doesn't normalize the types, you may want to
     use the [AssociatedTypes] equivalent instead.
 *)
-let type_decl_get_instantiated_field_rtypes (def : T.type_decl)
-    (opt_variant_id : T.VariantId.id option) (generics : T.rgeneric_args) :
-    T.rty list =
+let type_decl_get_instantiated_field_types (def : T.type_decl)
+    (opt_variant_id : T.VariantId.id option) (generics : T.generic_args) :
+    T.ty list =
   (* For now, check that there are no clauses - otherwise we might need
      to normalize the types *)
   assert (def.generics.trait_clauses = []);
@@ -284,11 +272,11 @@ let type_decl_get_instantiated_field_rtypes (def : T.type_decl)
     **IMPORTANT**: this function doesn't normalize the types, you may want to
     use the [AssociatedTypes] equivalent instead.
 *)
-let ctx_adt_get_instantiated_field_rtypes (ctx : C.eval_ctx)
+let ctx_adt_get_instantiated_field_types (ctx : C.eval_ctx)
     (def_id : T.TypeDeclId.id) (opt_variant_id : T.VariantId.id option)
-    (generics : T.rgeneric_args) : T.rty list =
+    (generics : T.generic_args) : T.ty list =
   let def = C.ctx_lookup_type_decl ctx def_id in
-  type_decl_get_instantiated_field_rtypes def opt_variant_id generics
+  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).
@@ -296,122 +284,55 @@ let ctx_adt_get_instantiated_field_rtypes (ctx : C.eval_ctx)
     **IMPORTANT**: this function doesn't normalize the types, you may want to
     use the [AssociatedTypes] equivalent instead.
  *)
-let ctx_adt_value_get_instantiated_field_rtypes (ctx : C.eval_ctx)
-    (adt : V.adt_value) (id : T.type_id) (generics : T.rgeneric_args) :
-    T.rty list =
+let ctx_adt_value_get_instantiated_field_types (ctx : C.eval_ctx)
+    (adt : V.adt_value) (id : T.type_id) (generics : T.generic_args) : T.ty list
+    =
   match id with
   | T.AdtId id ->
       (* Retrieve the types of the fields *)
-      ctx_adt_get_instantiated_field_rtypes ctx id adt.V.variant_id generics
+      ctx_adt_get_instantiated_field_types ctx id adt.V.variant_id generics
   | T.Tuple ->
       assert (generics.regions = []);
       generics.types
-  | T.Assumed aty -> (
+  | T.TAssumed aty -> (
       match aty with
-      | T.Box ->
+      | T.TBox ->
           assert (generics.regions = []);
           assert (List.length generics.types = 1);
           assert (generics.const_generics = []);
           generics.types
-      | T.Array | T.Slice | T.Str ->
+      | T.TArray | T.TSlice | T.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.
-
-    **IMPORTANT**: this function doesn't normalize the types, you may want to
-    use the [AssociatedTypes] equivalent instead.
-*)
-let type_decl_get_instantiated_field_etypes (def : T.type_decl)
-    (opt_variant_id : T.VariantId.id option) (generics : T.egeneric_args) :
-    T.ety 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 : T.erased_region T.trait_instance_id =
-    T.UnknownTrait __FUNCTION__
-  in
-  let { r_subst = _; ty_subst; cg_subst; tr_subst; tr_self } =
-    make_esubst_from_generics def.T.generics generics tr_self
-  in
-  let fields = TU.type_decl_get_fields def opt_variant_id in
-  List.map
-    (fun (f : T.field) ->
-      erase_regions_substitute_types ty_subst cg_subst tr_subst tr_self
-        f.T.field_ty)
-    fields
-
-(** Return the types of the properly instantiated ADT's variant, provided a
-    context.
-
-    **IMPORTANT**: this function doesn't normalize the types, you may want to
-    use the [AssociatedTypes] equivalent instead.
- *)
-let ctx_adt_get_instantiated_field_etypes (ctx : C.eval_ctx)
-    (def_id : T.TypeDeclId.id) (opt_variant_id : T.VariantId.id option)
-    (generics : T.egeneric_args) : T.ety list =
-  let def = C.ctx_lookup_type_decl ctx def_id in
-  type_decl_get_instantiated_field_etypes def opt_variant_id generics
-
-let statement_substitute_visitor
-    (subst : (T.erased_region, T.erased_region) subst) =
-  (* Keep in synch with [ty_substitute_visitor] *)
-  object
-    inherit [_] A.map_statement
-    method! visit_'r _ r = subst.r_subst r
-    method! visit_TypeVar _ 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 = subst.cg_subst id
-
-    method! visit_const_generic_var_id _ _ =
-      (* We should never get here because we reimplemented [visit_Var] *)
-      raise (Failure "Unexpected")
-
-    method! visit_Clause _ id = subst.tr_subst id
-    method! visit_Self _ = subst.tr_self
-  end
-
 (** Apply a type substitution to a place *)
-let place_substitute (subst : (T.erased_region, T.erased_region) subst)
-    (p : E.place) : E.place =
+let place_substitute (subst : subst) (p : E.place) : E.place =
   (* There is in fact nothing to do *)
-  (statement_substitute_visitor subst)#visit_place () p
+  (st_substitute_visitor subst)#visit_place () p
 
 (** Apply a type substitution to an operand *)
-let operand_substitute (subst : (T.erased_region, T.erased_region) subst)
-    (op : E.operand) : E.operand =
-  (statement_substitute_visitor subst)#visit_operand () op
+let operand_substitute (subst : subst) (op : E.operand) : E.operand =
+  (st_substitute_visitor subst)#visit_operand () op
 
 (** Apply a type substitution to an rvalue *)
-let rvalue_substitute (subst : (T.erased_region, T.erased_region) subst)
-    (rv : E.rvalue) : E.rvalue =
-  (statement_substitute_visitor subst)#visit_rvalue () rv
+let rvalue_substitute (subst : subst) (rv : E.rvalue) : E.rvalue =
+  (st_substitute_visitor subst)#visit_rvalue () rv
 
 (** Apply a type substitution to an assertion *)
-let assertion_substitute (subst : (T.erased_region, T.erased_region) subst)
-    (a : A.assertion) : A.assertion =
-  (statement_substitute_visitor subst)#visit_assertion () a
+let assertion_substitute (subst : subst) (a : A.assertion) : A.assertion =
+  (st_substitute_visitor subst)#visit_assertion () a
 
 (** Apply a type substitution to a call *)
-let call_substitute (subst : (T.erased_region, T.erased_region) subst)
-    (call : A.call) : A.call =
-  (statement_substitute_visitor subst)#visit_call () call
+let call_substitute (subst : subst) (call : A.call) : A.call =
+  (st_substitute_visitor subst)#visit_call () call
 
 (** Apply a type substitution to a statement *)
-let statement_substitute (subst : (T.erased_region, T.erased_region) subst)
-    (st : A.statement) : A.statement =
-  (statement_substitute_visitor subst)#visit_statement () st
+let statement_substitute (subst : subst) (st : A.statement) : A.statement =
+  (st_substitute_visitor subst)#visit_statement () st
 
 (** Apply a type substitution to a function body. Return the local variables
     and the body. *)
-let fun_body_substitute_in_body
-    (subst : (T.erased_region, T.erased_region) subst) (body : A.fun_body) :
+let fun_body_substitute_in_body (subst : subst) (body : A.fun_body) :
     A.var list * A.statement =
   let locals =
     List.map
@@ -421,10 +342,10 @@ let fun_body_substitute_in_body
   let body = statement_substitute subst body.body in
   (locals, body)
 
-let trait_type_constraint_substitute (subst : ('r1, 'r2) subst)
-    (ttc : 'r1 T.trait_type_constraint) : 'r2 T.trait_type_constraint =
+let trait_type_constraint_substitute (subst : subst)
+    (ttc : T.trait_type_constraint) : T.trait_type_constraint =
   let { T.trait_ref; generics; type_name; ty } = ttc in
-  let visitor = ty_substitute_visitor subst in
+  let visitor = st_substitute_visitor subst in
   let trait_ref = visitor#visit_trait_ref () trait_ref in
   let generics = visitor#visit_generic_args () generics in
   let ty = visitor#visit_ty () ty in
@@ -435,22 +356,24 @@ let trait_type_constraint_substitute (subst : ('r1, 'r2) subst)
     **IMPORTANT:** this function doesn't normalize the types.
  *)
 let substitute_signature (asubst : T.RegionGroupId.id -> V.AbstractionId.id)
-    (r_subst : T.RegionVarId.id -> T.RegionId.id)
-    (ty_subst : T.TypeVarId.id -> T.rty)
+    (r_subst : T.RegionId.id -> T.RegionId.id)
+    (ty_subst : T.TypeVarId.id -> T.ty)
     (cg_subst : T.ConstGenericVarId.id -> T.const_generic)
-    (tr_subst : T.TraitClauseId.id -> T.rtrait_instance_id)
-    (tr_self : T.rtrait_instance_id) (sg : A.fun_sig) : A.inst_fun_sig =
-  let r_subst' (r : T.RegionVarId.id T.region) : T.RegionId.id T.region =
-    match r with T.Static -> T.Static | T.Var rid -> T.Var (r_subst rid)
+    (tr_subst : T.TraitClauseId.id -> T.trait_instance_id)
+    (tr_self : T.trait_instance_id) (sg : A.fun_sig) : A.inst_fun_sig =
+  let r_subst' (r : T.region) : T.region =
+    match r with
+    | T.RStatic | T.RErased -> r
+    | T.RVar rid -> T.RVar (r_subst rid)
   in
   let subst = { r_subst = r_subst'; ty_subst; cg_subst; tr_subst; tr_self } in
   let inputs = List.map (ty_substitute subst) sg.A.inputs in
   let output = ty_substitute subst sg.A.output in
-  let subst_region_group (rg : T.region_var_group) : A.abs_region_group =
+  let subst_region_group (rg : T.region_group) : A.abs_region_group =
     let id = asubst rg.id in
     let regions = List.map r_subst rg.regions in
     let parents = List.map asubst rg.parents in
-    { id; regions; parents }
+    ({ id; regions; parents } : A.abs_region_group)
   in
   let regions_hierarchy = List.map subst_region_group sg.A.regions_hierarchy in
   let trait_type_constraints =
@@ -461,9 +384,9 @@ let substitute_signature (asubst : T.RegionGroupId.id -> V.AbstractionId.id)
   { A.inputs; output; regions_hierarchy; trait_type_constraints }
 
 (** Substitute variable identifiers in a type *)
-let ty_substitute_ids (ty_subst : T.TypeVarId.id -> T.TypeVarId.id)
-    (cg_subst : T.ConstGenericVarId.id -> T.ConstGenericVarId.id) (ty : 'r T.ty)
-    : 'r T.ty =
+let statement_substitute_ids (ty_subst : T.TypeVarId.id -> T.TypeVarId.id)
+    (cg_subst : T.ConstGenericVarId.id -> T.ConstGenericVarId.id) (ty : T.ty) :
+    T.ty =
   let open T in
   let visitor =
     object
@@ -476,80 +399,39 @@ let ty_substitute_ids (ty_subst : T.TypeVarId.id -> T.TypeVarId.id)
 
   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 (r_subst : T.RegionId.id -> T.RegionId.id)
-    (rvsubst : T.RegionVarId.id -> T.RegionVarId.id)
     (ty_subst : T.TypeVarId.id -> T.TypeVarId.id)
     (cg_subst : 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 (r_subst rid)
-
-      method! visit_type_var_id _ id = ty_subst id
-      method! visit_const_generic_var_id _ id = cg_subst 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 ty_subst cg_subst 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 = r_subst 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
+  object (self : 'self)
+    inherit [_] C.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 (r_subst : T.RegionId.id -> T.RegionId.id)
-    (rvsubst : T.RegionVarId.id -> T.RegionVarId.id)
     (ty_subst : T.TypeVarId.id -> T.TypeVarId.id)
     (cg_subst : 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 asubst _ = raise (Failure "Unreachable") in
-  (subst_ids_visitor r_subst rvsubst ty_subst cg_subst 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 (r_subst : T.RegionId.id -> T.RegionId.id)
     (v : V.typed_value) : V.typed_value =
@@ -558,61 +440,57 @@ let typed_value_subst_rids (r_subst : T.RegionId.id -> T.RegionId.id)
     (fun x -> x)
     (fun x -> x)
     (fun x -> x)
-    (fun x -> x)
     v
 
 let typed_avalue_subst_ids (r_subst : T.RegionId.id -> T.RegionId.id)
-    (rvsubst : T.RegionVarId.id -> T.RegionVarId.id)
     (ty_subst : T.TypeVarId.id -> T.TypeVarId.id)
     (cg_subst : 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 asubst _ = raise (Failure "Unreachable") in
-  (subst_ids_visitor r_subst rvsubst ty_subst cg_subst ssubst bsubst asubst)
-    #visit_typed_avalue v
+  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 : T.RegionId.id -> T.RegionId.id)
-    (rvsubst : T.RegionVarId.id -> T.RegionVarId.id)
     (ty_subst : T.TypeVarId.id -> T.TypeVarId.id)
     (cg_subst : 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 r_subst rvsubst ty_subst cg_subst ssubst bsubst asubst)
-    #visit_abs x
+  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 : T.RegionId.id -> T.RegionId.id)
-    (rvsubst : T.RegionVarId.id -> T.RegionVarId.id)
     (ty_subst : T.TypeVarId.id -> T.TypeVarId.id)
     (cg_subst : 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 r_subst rvsubst ty_subst cg_subst ssubst bsubst asubst)
-    #visit_env x
+  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 : T.RegionId.id -> T.RegionId.id)
     (x : V.typed_avalue) : V.typed_avalue =
   let asubst _ = raise (Failure "Unreachable") in
-  (subst_ids_visitor r_subst
-     (fun x -> x)
-     (fun x -> x)
-     (fun x -> x)
-     (fun x -> x)
-     (fun x -> x)
-     asubst)
-    #visit_typed_avalue
-    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 : T.RegionId.id -> T.RegionId.id) (x : C.env) :
     C.env =
-  (subst_ids_visitor r_subst
-     (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)
+      (fun x -> x)
+  in
+  vis#visit_env () x
-- 
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