Cleanup and reorganize

8 files changed, 492 insertions, 476 deletions

diff --git a/src/InterpreterBorrows.ml b/src/InterpreterBorrows.ml
index b60f0973..38c79b66 100644
--- a/src/InterpreterBorrows.ml
+++ b/src/InterpreterBorrows.ml
@@ -5,6 +5,7 @@ module Subst = Substitute
 module L = Logging
 open Utils
 open InterpreterUtils
+open InterpreterBorrowsCore
 open InterpreterProjectors
 
 (** Auxiliary function to end borrows: lookup a borrow in the environment,
diff --git a/src/InterpreterBorrowsCore.ml b/src/InterpreterBorrowsCore.ml
new file mode 100644
index 00000000..ccc259f5
--- /dev/null
+++ b/src/InterpreterBorrowsCore.ml
@@ -0,0 +1,459 @@
+(* This file defines the basic blocks to implement the semantics of borrows.
+ * Note that those functions are not only used in InterpreterBorrows, but
+ * also in Invariants or InterpreterProjectors *)
+
+module T = Types
+module V = Values
+module C = Contexts
+module Subst = Substitute
+module L = Logging
+open Utils
+open InterpreterUtils
+
+(** TODO: cleanup this a bit, once we have a better understanding about
+    what we need.
+    TODO: I'm not sure in which file this should be moved... *)
+type exploration_kind = {
+  enter_shared_loans : bool;
+  enter_mut_borrows : bool;
+  enter_abs : bool;
+      (** Note that if we allow to enter abs, we don't check whether we enter
+          mutable/shared loans or borrows: there are no use cases requiring
+          a finer control. *)
+}
+(** This record controls how some generic helper lookup/update
+    functions behave, by restraining the kind of therms they can enter.
+*)
+
+let ek_all : exploration_kind =
+  { enter_shared_loans = true; enter_mut_borrows = true; enter_abs = true }
+
+(** The following type identifies the relative position of expressions (in
+    particular borrows) in other expressions.
+    
+    For instance, it is used to control [end_borrow]: we usually only allow
+    to end "outer" borrows, unless we perform a drop.
+*)
+type inner_outer = Inner | Outer
+
+type borrow_ids = Borrows of V.BorrowId.Set.t | Borrow of V.BorrowId.id
+
+exception FoundBorrowIds of borrow_ids
+
+type outer_borrows_or_abs =
+  | OuterBorrows of borrow_ids
+  | OuterAbs of V.AbstractionId.id
+
+let update_if_none opt x = match opt with None -> Some x | _ -> opt
+
+exception FoundOuter of outer_borrows_or_abs
+(** Utility exception *)
+
+(** Lookup a loan content.
+
+    The loan is referred to by a borrow id.
+
+    TODO: group abs_or_var_id and g_loan_content. 
+ *)
+let lookup_loan_opt (ek : exploration_kind) (l : V.BorrowId.id)
+    (ctx : C.eval_ctx) : (abs_or_var_id * g_loan_content) option =
+  (* We store here whether we are inside an abstraction or a value - note that we
+   * could also track that with the environment, it would probably be more idiomatic
+   * and cleaner *)
+  let abs_or_var : abs_or_var_id option ref = ref None in
+
+  let obj =
+    object
+      inherit [_] C.iter_eval_ctx as super
+
+      method! visit_borrow_content env bc =
+        match bc with
+        | V.SharedBorrow bid ->
+            (* Nothing specific to do *)
+            super#visit_SharedBorrow env bid
+        | V.InactivatedMutBorrow bid ->
+            (* Nothing specific to do *)
+            super#visit_InactivatedMutBorrow env bid
+        | V.MutBorrow (bid, mv) ->
+            (* Control the dive *)
+            if ek.enter_mut_borrows then super#visit_MutBorrow env bid mv
+            else ()
+
+      method! visit_loan_content env lc =
+        match lc with
+        | V.SharedLoan (bids, sv) ->
+            (* Check if this is the loan we are looking for, and control the dive *)
+            if V.BorrowId.Set.mem l bids then
+              raise (FoundGLoanContent (Concrete lc))
+            else if ek.enter_shared_loans then
+              super#visit_SharedLoan env bids sv
+            else ()
+        | V.MutLoan bid ->
+            (* Check if this is the loan we are looking for *)
+            if bid = l then raise (FoundGLoanContent (Concrete lc))
+            else super#visit_MutLoan env bid
+      (** We reimplement [visit_Loan] (rather than the more precise functions
+          [visit_SharedLoan], etc.) on purpose: as we have an exhaustive match
+          below, we are more resilient to definition updates (the compiler
+          is our friend).
+      *)
+
+      method! visit_aloan_content env lc =
+        match lc with
+        | V.AMutLoan (bid, av) ->
+            if bid = l then raise (FoundGLoanContent (Abstract lc))
+            else super#visit_AMutLoan env bid av
+        | V.ASharedLoan (bids, v, av) ->
+            if V.BorrowId.Set.mem l bids then
+              raise (FoundGLoanContent (Abstract lc))
+            else super#visit_ASharedLoan env bids v av
+        | V.AEndedMutLoan { given_back; child } ->
+            super#visit_AEndedMutLoan env given_back child
+        | V.AEndedSharedLoan (v, av) -> super#visit_AEndedSharedLoan env v av
+        | V.AIgnoredMutLoan (bid, av) -> super#visit_AIgnoredMutLoan env bid av
+        | V.AEndedIgnoredMutLoan { given_back; child } ->
+            super#visit_AEndedIgnoredMutLoan env given_back child
+        | V.AIgnoredSharedLoan av -> super#visit_AIgnoredSharedLoan env av
+      (** Note that we don't control diving inside the abstractions: if we
+          allow to dive inside abstractions, we allow to go anywhere
+          (because there are no use cases requiring finer control) *)
+
+      method! visit_Var env bv v =
+        assert (Option.is_none !abs_or_var);
+        abs_or_var := Some (VarId bv.C.index);
+        super#visit_Var env bv v;
+        abs_or_var := None
+
+      method! visit_Abs env abs =
+        assert (Option.is_none !abs_or_var);
+        if ek.enter_abs then (
+          abs_or_var := Some (AbsId abs.V.abs_id);
+          super#visit_Abs env abs)
+        else ()
+    end
+  in
+  (* We use exceptions *)
+  try
+    obj#visit_eval_ctx () ctx;
+    None
+  with FoundGLoanContent lc -> (
+    match !abs_or_var with
+    | Some abs_or_var -> Some (abs_or_var, lc)
+    | None -> failwith "Inconsistent state")
+
+(** Lookup a loan content.
+
+    The loan is referred to by a borrow id.
+    Raises an exception if no loan was found.
+ *)
+let lookup_loan (ek : exploration_kind) (l : V.BorrowId.id) (ctx : C.eval_ctx) :
+    abs_or_var_id * g_loan_content =
+  match lookup_loan_opt ek l ctx with
+  | None -> failwith "Unreachable"
+  | Some res -> res
+
+(** Update a loan content.
+
+    The loan is referred to by a borrow id.
+
+    This is a helper function: it might break invariants.
+ *)
+let update_loan (ek : exploration_kind) (l : V.BorrowId.id)
+    (nlc : V.loan_content) (ctx : C.eval_ctx) : C.eval_ctx =
+  (* We use a reference to check that we update exactly one loan: when updating
+   * inside values, we check we don't update more than one loan. Then, upon
+   * returning we check that we updated at least once. *)
+  let r = ref false in
+  let update () : V.loan_content =
+    assert (not !r);
+    r := true;
+    nlc
+  in
+
+  let obj =
+    object
+      inherit [_] C.map_eval_ctx as super
+
+      method! visit_borrow_content env bc =
+        match bc with
+        | V.SharedBorrow _ | V.InactivatedMutBorrow _ ->
+            (* Nothing specific to do *)
+            super#visit_borrow_content env bc
+        | V.MutBorrow (bid, mv) ->
+            (* Control the dive into mutable borrows *)
+            if ek.enter_mut_borrows then super#visit_MutBorrow env bid mv
+            else V.MutBorrow (bid, mv)
+
+      method! visit_loan_content env lc =
+        match lc with
+        | V.SharedLoan (bids, sv) ->
+            (* Shared loan: check if this is the loan we are looking for, and
+               control the dive. *)
+            if V.BorrowId.Set.mem l bids then update ()
+            else if ek.enter_shared_loans then
+              super#visit_SharedLoan env bids sv
+            else V.SharedLoan (bids, sv)
+        | V.MutLoan bid ->
+            (* Mut loan: checks if this is the loan we are looking for *)
+            if bid = l then update () else super#visit_MutLoan env bid
+      (** We reimplement [visit_loan_content] (rather than one of the sub-
+          functions) on purpose: exhaustive matches are good for maintenance *)
+
+      method! visit_abs env abs =
+        if ek.enter_abs then super#visit_abs env abs else abs
+      (** Note that once inside the abstractions, we don't control diving
+          (there are no use cases requiring finer control).
+          Also, as we give back a [loan_content] (and not an [aloan_content])
+          we don't need to do reimplement the visit functions for the values
+          inside the abstractions (rk.: there may be "concrete" values inside
+          abstractions, so there is a utility in diving inside). *)
+    end
+  in
+
+  let ctx = obj#visit_eval_ctx () ctx in
+  (* Check that we updated at least one loan *)
+  assert !r;
+  ctx
+
+(** Update a abstraction loan content.
+
+    The loan is referred to by a borrow id.
+
+    This is a helper function: it might break invariants.
+ *)
+let update_aloan (ek : exploration_kind) (l : V.BorrowId.id)
+    (nlc : V.aloan_content) (ctx : C.eval_ctx) : C.eval_ctx =
+  (* We use a reference to check that we update exactly one loan: when updating
+   * inside values, we check we don't update more than one loan. Then, upon
+   * returning we check that we updated at least once. *)
+  let r = ref false in
+  let update () : V.aloan_content =
+    assert (not !r);
+    r := true;
+    nlc
+  in
+
+  let obj =
+    object
+      inherit [_] C.map_eval_ctx as super
+
+      method! visit_aloan_content env lc =
+        match lc with
+        | V.AMutLoan (bid, av) ->
+            if bid = l then update () else super#visit_AMutLoan env bid av
+        | V.ASharedLoan (bids, v, av) ->
+            if V.BorrowId.Set.mem l bids then update ()
+            else super#visit_ASharedLoan env bids v av
+        | V.AEndedMutLoan { given_back; child } ->
+            super#visit_AEndedMutLoan env given_back child
+        | V.AEndedSharedLoan (v, av) -> super#visit_AEndedSharedLoan env v av
+        | V.AIgnoredMutLoan (bid, av) -> super#visit_AIgnoredMutLoan env bid av
+        | V.AEndedIgnoredMutLoan { given_back; child } ->
+            super#visit_AEndedIgnoredMutLoan env given_back child
+        | V.AIgnoredSharedLoan av -> super#visit_AIgnoredSharedLoan env av
+
+      method! visit_abs env abs =
+        if ek.enter_abs then super#visit_abs env abs else abs
+      (** Note that once inside the abstractions, we don't control diving
+          (there are no use cases requiring finer control). *)
+    end
+  in
+
+  let ctx = obj#visit_eval_ctx () ctx in
+  (* Check that we updated at least one loan *)
+  assert !r;
+  ctx
+
+(** Lookup a borrow content from a borrow id. *)
+let lookup_borrow_opt (ek : exploration_kind) (l : V.BorrowId.id)
+    (ctx : C.eval_ctx) : g_borrow_content option =
+  let obj =
+    object
+      inherit [_] C.iter_eval_ctx as super
+
+      method! visit_borrow_content env bc =
+        match bc with
+        | V.MutBorrow (bid, mv) ->
+            (* Check the borrow id and control the dive *)
+            if bid = l then raise (FoundGBorrowContent (Concrete bc))
+            else if ek.enter_mut_borrows then super#visit_MutBorrow env bid mv
+            else ()
+        | V.SharedBorrow bid ->
+            (* Check the borrow id *)
+            if bid = l then raise (FoundGBorrowContent (Concrete bc)) else ()
+        | V.InactivatedMutBorrow bid ->
+            (* Check the borrow id *)
+            if bid = l then raise (FoundGBorrowContent (Concrete bc)) else ()
+
+      method! visit_loan_content env lc =
+        match lc with
+        | V.MutLoan bid ->
+            (* Nothing special to do *) super#visit_MutLoan env bid
+        | V.SharedLoan (bids, sv) ->
+            (* Control the dive *)
+            if ek.enter_shared_loans then super#visit_SharedLoan env bids sv
+            else ()
+
+      method! visit_aborrow_content env bc =
+        match bc with
+        | V.AMutBorrow (bid, av) ->
+            if bid = l then raise (FoundGBorrowContent (Abstract bc))
+            else super#visit_AMutBorrow env bid av
+        | V.ASharedBorrow bid ->
+            if bid = l then raise (FoundGBorrowContent (Abstract bc))
+            else super#visit_ASharedBorrow env bid
+        | V.AIgnoredMutBorrow av -> super#visit_AIgnoredMutBorrow env av
+        | V.AProjSharedBorrow asb ->
+            if borrow_in_asb l asb then
+              raise (FoundGBorrowContent (Abstract bc))
+            else ()
+
+      method! visit_abs env abs =
+        if ek.enter_abs then super#visit_abs env abs else ()
+    end
+  in
+  (* We use exceptions *)
+  try
+    obj#visit_eval_ctx () ctx;
+    None
+  with FoundGBorrowContent lc -> Some lc
+
+(** Lookup a borrow content from a borrow id.
+
+    Raise an exception if no loan was found
+*)
+let lookup_borrow (ek : exploration_kind) (l : V.BorrowId.id) (ctx : C.eval_ctx)
+    : g_borrow_content =
+  match lookup_borrow_opt ek l ctx with
+  | None -> failwith "Unreachable"
+  | Some lc -> lc
+
+(** Update a borrow content.
+
+    The borrow is referred to by a borrow id.
+
+    This is a helper function: it might break invariants.   
+ *)
+let update_borrow (ek : exploration_kind) (l : V.BorrowId.id)
+    (nbc : V.borrow_content) (ctx : C.eval_ctx) : C.eval_ctx =
+  (* We use a reference to check that we update exactly one borrow: when updating
+   * inside values, we check we don't update more than one borrow. Then, upon
+   * returning we check that we updated at least once. *)
+  let r = ref false in
+  let update () : V.borrow_content =
+    assert (not !r);
+    r := true;
+    nbc
+  in
+
+  let obj =
+    object
+      inherit [_] C.map_eval_ctx as super
+
+      method! visit_borrow_content env bc =
+        match bc with
+        | V.MutBorrow (bid, mv) ->
+            (* Check the id and control dive *)
+            if bid = l then update ()
+            else if ek.enter_mut_borrows then super#visit_MutBorrow env bid mv
+            else V.MutBorrow (bid, mv)
+        | V.SharedBorrow bid ->
+            (* Check the id *)
+            if bid = l then update () else super#visit_SharedBorrow env bid
+        | V.InactivatedMutBorrow bid ->
+            (* Check the id *)
+            if bid = l then update ()
+            else super#visit_InactivatedMutBorrow env bid
+
+      method! visit_loan_content env lc =
+        match lc with
+        | V.SharedLoan (bids, sv) ->
+            (* Control the dive *)
+            if ek.enter_shared_loans then super#visit_SharedLoan env bids sv
+            else V.SharedLoan (bids, sv)
+        | V.MutLoan bid ->
+            (* Nothing specific to do *)
+            super#visit_MutLoan env bid
+
+      method! visit_abs env abs =
+        if ek.enter_abs then super#visit_abs env abs else abs
+    end
+  in
+
+  let ctx = obj#visit_eval_ctx () ctx in
+  (* Check that we updated at least one borrow *)
+  assert !r;
+  ctx
+
+(** Update an abstraction borrow content.
+
+    The borrow is referred to by a borrow id.
+
+    This is a helper function: it might break invariants.     
+ *)
+let update_aborrow (ek : exploration_kind) (l : V.BorrowId.id) (nv : V.avalue)
+    (ctx : C.eval_ctx) : C.eval_ctx =
+  (* We use a reference to check that we update exactly one borrow: when updating
+   * inside values, we check we don't update more than one borrow. Then, upon
+   * returning we check that we updated at least once. *)
+  let r = ref false in
+  let update () : V.avalue =
+    assert (not !r);
+    r := true;
+    nv
+  in
+
+  let obj =
+    object
+      inherit [_] C.map_eval_ctx as super
+
+      method! visit_ABorrow env bc =
+        match bc with
+        | V.AMutBorrow (bid, av) ->
+            if bid = l then update ()
+            else V.ABorrow (super#visit_AMutBorrow env bid av)
+        | V.ASharedBorrow bid ->
+            if bid = l then update ()
+            else V.ABorrow (super#visit_ASharedBorrow env bid)
+        | V.AIgnoredMutBorrow av ->
+            V.ABorrow (super#visit_AIgnoredMutBorrow env av)
+        | V.AProjSharedBorrow asb ->
+            if borrow_in_asb l asb then update ()
+            else V.ABorrow (super#visit_AProjSharedBorrow env asb)
+
+      method! visit_abs env abs =
+        if ek.enter_abs then super#visit_abs env abs else abs
+    end
+  in
+
+  let ctx = obj#visit_eval_ctx () ctx in
+  (* Check that we updated at least one borrow *)
+  assert !r;
+  ctx
+
+(** Auxiliary function: see its usage in [end_borrow_get_borrow_in_value] *)
+let update_outer_borrows (io : inner_outer)
+    (outer : V.AbstractionId.id option * borrow_ids option) (x : borrow_ids) :
+    V.AbstractionId.id option * borrow_ids option =
+  match io with
+  | Inner ->
+      (* If we can end inner borrows, we don't keep track of the outer borrows *)
+      outer
+  | Outer ->
+      let abs, opt = outer in
+      (abs, update_if_none opt x)
+
+(** Return the first loan we find in a value *)
+let get_first_loan_in_value (v : V.typed_value) : V.loan_content option =
+  let obj =
+    object
+      inherit [_] V.iter_typed_value
+
+      method! visit_loan_content _ lc = raise (FoundLoanContent lc)
+    end
+  in
+  (* We use exceptions *)
+  try
+    obj#visit_typed_value () v;
+    None
+  with FoundLoanContent lc -> Some lc
diff --git a/src/InterpreterPaths.ml b/src/InterpreterPaths.ml
index e8f5eefc..841c22cf 100644
--- a/src/InterpreterPaths.ml
+++ b/src/InterpreterPaths.ml
@@ -6,6 +6,7 @@ module Subst = Substitute
 module L = Logging
 module S = Synthesis
 open InterpreterUtils
+open InterpreterBorrowsCore
 open InterpreterBorrows
 open InterpreterExpansion
 
diff --git a/src/InterpreterProjectors.ml b/src/InterpreterProjectors.ml
index c3fd0708..92ea6483 100644
--- a/src/InterpreterProjectors.ml
+++ b/src/InterpreterProjectors.ml
@@ -8,6 +8,7 @@ open TypesUtils
 open ValuesUtils
 open Utils
 open InterpreterUtils
+open InterpreterBorrowsCore
 
 (** Auxiliary function.
 
diff --git a/src/InterpreterUtils.ml b/src/InterpreterUtils.ml
index be3d606c..0b7d8f21 100644
--- a/src/InterpreterUtils.ml
+++ b/src/InterpreterUtils.ml
@@ -29,41 +29,14 @@ let statement_to_string ctx =
 let same_symbolic_id (sv0 : V.symbolic_value) (sv1 : V.symbolic_value) : bool =
   sv0.V.sv_id = sv1.V.sv_id
 
-(* TODO: move *)
 let mk_var (index : V.VarId.id) (name : string option) (var_ty : T.ety) : A.var
     =
   { A.index; name; var_ty }
 
-(** Small helper *)
+(** Small helper - TODO: move *)
 let mk_place_from_var_id (var_id : V.VarId.id) : E.place =
   { var_id; projection = [] }
 
-(** Deconstruct a type of the form `Box<T>` to retrieve the `T` inside *)
-let ty_get_box (box_ty : T.ety) : T.ety =
-  match box_ty with
-  | T.Adt (T.Assumed T.Box, [], [ boxed_ty ]) -> boxed_ty
-  | _ -> failwith "Not a boxed type"
-
-(** Deconstruct a type of the form `&T` or `&mut T` to retrieve the `T` (and
-    the borrow kind, etc.)
- *)
-let ty_get_ref (ty : T.ety) : T.erased_region * T.ety * T.ref_kind =
-  match ty with
-  | T.Ref (r, ty, ref_kind) -> (r, ty, ref_kind)
-  | _ -> failwith "Not a ref type"
-
-let mk_ref_ty (r : 'r) (ty : 'r T.ty) (ref_kind : T.ref_kind) : 'r T.ty =
-  T.Ref (r, ty, ref_kind)
-
-(** Make a box type *)
-let mk_box_ty (ty : 'r T.ty) : 'r T.ty = T.Adt (T.Assumed T.Box, [], [ ty ])
-
-(** Box a value *)
-let mk_box_value (v : V.typed_value) : V.typed_value =
-  let box_ty = mk_box_ty v.V.ty in
-  let box_v = V.Adt { variant_id = None; field_values = [ v ] } in
-  mk_typed_value box_ty box_v
-
 (** Create a fresh symbolic proj comp *)
 let mk_fresh_symbolic_proj_comp (ended_regions : T.RegionId.set_t) (ty : T.rty)
     (ctx : C.eval_ctx) : C.eval_ctx * V.symbolic_proj_comp =
@@ -125,22 +98,6 @@ let remove_borrow_from_asb (bid : V.BorrowId.id)
   assert (!removed = 1);
   asb
 
-(* TODO: cleanup this a bit, once we have a better understanding about what we need *)
-type exploration_kind = {
-  enter_shared_loans : bool;
-  enter_mut_borrows : bool;
-  enter_abs : bool;
-      (** Note that if we allow to enter abs, we don't check whether we enter
-          mutable/shared loans or borrows: there are no use cases requiring
-          a finer control. *)
-}
-(** This record controls how some generic helper lookup/update
-    functions behave, by restraining the kind of therms they can enter.
-*)
-
-let ek_all : exploration_kind =
-  { enter_shared_loans = true; enter_mut_borrows = true; enter_abs = true }
-
 (** We sometimes need to return a value whose type may vary depending on
     whether we find it in a "concrete" value or an abstraction (ex.: loan
     contents when we perform environment lookups by using borrow ids) *)
@@ -244,388 +201,6 @@ let symbolic_value_id_in_ctx (sv_id : V.SymbolicValueId.id) (ctx : C.eval_ctx) :
     false
   with Found -> true
 
-(** Lookup a loan content.
-
-    The loan is referred to by a borrow id.
-
-    TODO: group abs_or_var_id and g_loan_content. 
- *)
-let lookup_loan_opt (ek : exploration_kind) (l : V.BorrowId.id)
-    (ctx : C.eval_ctx) : (abs_or_var_id * g_loan_content) option =
-  (* We store here whether we are inside an abstraction or a value - note that we
-   * could also track that with the environment, it would probably be more idiomatic
-   * and cleaner *)
-  let abs_or_var : abs_or_var_id option ref = ref None in
-
-  let obj =
-    object
-      inherit [_] C.iter_eval_ctx as super
-
-      method! visit_borrow_content env bc =
-        match bc with
-        | V.SharedBorrow bid ->
-            (* Nothing specific to do *)
-            super#visit_SharedBorrow env bid
-        | V.InactivatedMutBorrow bid ->
-            (* Nothing specific to do *)
-            super#visit_InactivatedMutBorrow env bid
-        | V.MutBorrow (bid, mv) ->
-            (* Control the dive *)
-            if ek.enter_mut_borrows then super#visit_MutBorrow env bid mv
-            else ()
-
-      method! visit_loan_content env lc =
-        match lc with
-        | V.SharedLoan (bids, sv) ->
-            (* Check if this is the loan we are looking for, and control the dive *)
-            if V.BorrowId.Set.mem l bids then
-              raise (FoundGLoanContent (Concrete lc))
-            else if ek.enter_shared_loans then
-              super#visit_SharedLoan env bids sv
-            else ()
-        | V.MutLoan bid ->
-            (* Check if this is the loan we are looking for *)
-            if bid = l then raise (FoundGLoanContent (Concrete lc))
-            else super#visit_MutLoan env bid
-      (** We reimplement [visit_Loan] (rather than the more precise functions
-          [visit_SharedLoan], etc.) on purpose: as we have an exhaustive match
-          below, we are more resilient to definition updates (the compiler
-          is our friend).
-      *)
-
-      method! visit_aloan_content env lc =
-        match lc with
-        | V.AMutLoan (bid, av) ->
-            if bid = l then raise (FoundGLoanContent (Abstract lc))
-            else super#visit_AMutLoan env bid av
-        | V.ASharedLoan (bids, v, av) ->
-            if V.BorrowId.Set.mem l bids then
-              raise (FoundGLoanContent (Abstract lc))
-            else super#visit_ASharedLoan env bids v av
-        | V.AEndedMutLoan { given_back; child } ->
-            super#visit_AEndedMutLoan env given_back child
-        | V.AEndedSharedLoan (v, av) -> super#visit_AEndedSharedLoan env v av
-        | V.AIgnoredMutLoan (bid, av) -> super#visit_AIgnoredMutLoan env bid av
-        | V.AEndedIgnoredMutLoan { given_back; child } ->
-            super#visit_AEndedIgnoredMutLoan env given_back child
-        | V.AIgnoredSharedLoan av -> super#visit_AIgnoredSharedLoan env av
-      (** Note that we don't control diving inside the abstractions: if we
-          allow to dive inside abstractions, we allow to go anywhere
-          (because there are no use cases requiring finer control) *)
-
-      method! visit_Var env bv v =
-        assert (Option.is_none !abs_or_var);
-        abs_or_var := Some (VarId bv.C.index);
-        super#visit_Var env bv v;
-        abs_or_var := None
-
-      method! visit_Abs env abs =
-        assert (Option.is_none !abs_or_var);
-        if ek.enter_abs then (
-          abs_or_var := Some (AbsId abs.V.abs_id);
-          super#visit_Abs env abs)
-        else ()
-    end
-  in
-  (* We use exceptions *)
-  try
-    obj#visit_eval_ctx () ctx;
-    None
-  with FoundGLoanContent lc -> (
-    match !abs_or_var with
-    | Some abs_or_var -> Some (abs_or_var, lc)
-    | None -> failwith "Inconsistent state")
-
-(** Lookup a loan content.
-
-    The loan is referred to by a borrow id.
-    Raises an exception if no loan was found.
- *)
-let lookup_loan (ek : exploration_kind) (l : V.BorrowId.id) (ctx : C.eval_ctx) :
-    abs_or_var_id * g_loan_content =
-  match lookup_loan_opt ek l ctx with
-  | None -> failwith "Unreachable"
-  | Some res -> res
-
-(** Update a loan content.
-
-    The loan is referred to by a borrow id.
-
-    This is a helper function: it might break invariants.
- *)
-let update_loan (ek : exploration_kind) (l : V.BorrowId.id)
-    (nlc : V.loan_content) (ctx : C.eval_ctx) : C.eval_ctx =
-  (* We use a reference to check that we update exactly one loan: when updating
-   * inside values, we check we don't update more than one loan. Then, upon
-   * returning we check that we updated at least once. *)
-  let r = ref false in
-  let update () : V.loan_content =
-    assert (not !r);
-    r := true;
-    nlc
-  in
-
-  let obj =
-    object
-      inherit [_] C.map_eval_ctx as super
-
-      method! visit_borrow_content env bc =
-        match bc with
-        | V.SharedBorrow _ | V.InactivatedMutBorrow _ ->
-            (* Nothing specific to do *)
-            super#visit_borrow_content env bc
-        | V.MutBorrow (bid, mv) ->
-            (* Control the dive into mutable borrows *)
-            if ek.enter_mut_borrows then super#visit_MutBorrow env bid mv
-            else V.MutBorrow (bid, mv)
-
-      method! visit_loan_content env lc =
-        match lc with
-        | V.SharedLoan (bids, sv) ->
-            (* Shared loan: check if this is the loan we are looking for, and
-               control the dive. *)
-            if V.BorrowId.Set.mem l bids then update ()
-            else if ek.enter_shared_loans then
-              super#visit_SharedLoan env bids sv
-            else V.SharedLoan (bids, sv)
-        | V.MutLoan bid ->
-            (* Mut loan: checks if this is the loan we are looking for *)
-            if bid = l then update () else super#visit_MutLoan env bid
-      (** We reimplement [visit_loan_content] (rather than one of the sub-
-          functions) on purpose: exhaustive matches are good for maintenance *)
-
-      method! visit_abs env abs =
-        if ek.enter_abs then super#visit_abs env abs else abs
-      (** Note that once inside the abstractions, we don't control diving
-          (there are no use cases requiring finer control).
-          Also, as we give back a [loan_content] (and not an [aloan_content])
-          we don't need to do reimplement the visit functions for the values
-          inside the abstractions (rk.: there may be "concrete" values inside
-          abstractions, so there is a utility in diving inside). *)
-    end
-  in
-
-  let ctx = obj#visit_eval_ctx () ctx in
-  (* Check that we updated at least one loan *)
-  assert !r;
-  ctx
-
-(** Update a abstraction loan content.
-
-    The loan is referred to by a borrow id.
-
-    This is a helper function: it might break invariants.
- *)
-let update_aloan (ek : exploration_kind) (l : V.BorrowId.id)
-    (nlc : V.aloan_content) (ctx : C.eval_ctx) : C.eval_ctx =
-  (* We use a reference to check that we update exactly one loan: when updating
-   * inside values, we check we don't update more than one loan. Then, upon
-   * returning we check that we updated at least once. *)
-  let r = ref false in
-  let update () : V.aloan_content =
-    assert (not !r);
-    r := true;
-    nlc
-  in
-
-  let obj =
-    object
-      inherit [_] C.map_eval_ctx as super
-
-      method! visit_aloan_content env lc =
-        match lc with
-        | V.AMutLoan (bid, av) ->
-            if bid = l then update () else super#visit_AMutLoan env bid av
-        | V.ASharedLoan (bids, v, av) ->
-            if V.BorrowId.Set.mem l bids then update ()
-            else super#visit_ASharedLoan env bids v av
-        | V.AEndedMutLoan { given_back; child } ->
-            super#visit_AEndedMutLoan env given_back child
-        | V.AEndedSharedLoan (v, av) -> super#visit_AEndedSharedLoan env v av
-        | V.AIgnoredMutLoan (bid, av) -> super#visit_AIgnoredMutLoan env bid av
-        | V.AEndedIgnoredMutLoan { given_back; child } ->
-            super#visit_AEndedIgnoredMutLoan env given_back child
-        | V.AIgnoredSharedLoan av -> super#visit_AIgnoredSharedLoan env av
-
-      method! visit_abs env abs =
-        if ek.enter_abs then super#visit_abs env abs else abs
-      (** Note that once inside the abstractions, we don't control diving
-          (there are no use cases requiring finer control). *)
-    end
-  in
-
-  let ctx = obj#visit_eval_ctx () ctx in
-  (* Check that we updated at least one loan *)
-  assert !r;
-  ctx
-
-(** Lookup a borrow content from a borrow id. *)
-let lookup_borrow_opt (ek : exploration_kind) (l : V.BorrowId.id)
-    (ctx : C.eval_ctx) : g_borrow_content option =
-  let obj =
-    object
-      inherit [_] C.iter_eval_ctx as super
-
-      method! visit_borrow_content env bc =
-        match bc with
-        | V.MutBorrow (bid, mv) ->
-            (* Check the borrow id and control the dive *)
-            if bid = l then raise (FoundGBorrowContent (Concrete bc))
-            else if ek.enter_mut_borrows then super#visit_MutBorrow env bid mv
-            else ()
-        | V.SharedBorrow bid ->
-            (* Check the borrow id *)
-            if bid = l then raise (FoundGBorrowContent (Concrete bc)) else ()
-        | V.InactivatedMutBorrow bid ->
-            (* Check the borrow id *)
-            if bid = l then raise (FoundGBorrowContent (Concrete bc)) else ()
-
-      method! visit_loan_content env lc =
-        match lc with
-        | V.MutLoan bid ->
-            (* Nothing special to do *) super#visit_MutLoan env bid
-        | V.SharedLoan (bids, sv) ->
-            (* Control the dive *)
-            if ek.enter_shared_loans then super#visit_SharedLoan env bids sv
-            else ()
-
-      method! visit_aborrow_content env bc =
-        match bc with
-        | V.AMutBorrow (bid, av) ->
-            if bid = l then raise (FoundGBorrowContent (Abstract bc))
-            else super#visit_AMutBorrow env bid av
-        | V.ASharedBorrow bid ->
-            if bid = l then raise (FoundGBorrowContent (Abstract bc))
-            else super#visit_ASharedBorrow env bid
-        | V.AIgnoredMutBorrow av -> super#visit_AIgnoredMutBorrow env av
-        | V.AProjSharedBorrow asb ->
-            if borrow_in_asb l asb then
-              raise (FoundGBorrowContent (Abstract bc))
-            else ()
-
-      method! visit_abs env abs =
-        if ek.enter_abs then super#visit_abs env abs else ()
-    end
-  in
-  (* We use exceptions *)
-  try
-    obj#visit_eval_ctx () ctx;
-    None
-  with FoundGBorrowContent lc -> Some lc
-
-(** Lookup a borrow content from a borrow id.
-
-    Raise an exception if no loan was found
-*)
-let lookup_borrow (ek : exploration_kind) (l : V.BorrowId.id) (ctx : C.eval_ctx)
-    : g_borrow_content =
-  match lookup_borrow_opt ek l ctx with
-  | None -> failwith "Unreachable"
-  | Some lc -> lc
-
-(** Update a borrow content.
-
-    The borrow is referred to by a borrow id.
-
-    This is a helper function: it might break invariants.   
- *)
-let update_borrow (ek : exploration_kind) (l : V.BorrowId.id)
-    (nbc : V.borrow_content) (ctx : C.eval_ctx) : C.eval_ctx =
-  (* We use a reference to check that we update exactly one borrow: when updating
-   * inside values, we check we don't update more than one borrow. Then, upon
-   * returning we check that we updated at least once. *)
-  let r = ref false in
-  let update () : V.borrow_content =
-    assert (not !r);
-    r := true;
-    nbc
-  in
-
-  let obj =
-    object
-      inherit [_] C.map_eval_ctx as super
-
-      method! visit_borrow_content env bc =
-        match bc with
-        | V.MutBorrow (bid, mv) ->
-            (* Check the id and control dive *)
-            if bid = l then update ()
-            else if ek.enter_mut_borrows then super#visit_MutBorrow env bid mv
-            else V.MutBorrow (bid, mv)
-        | V.SharedBorrow bid ->
-            (* Check the id *)
-            if bid = l then update () else super#visit_SharedBorrow env bid
-        | V.InactivatedMutBorrow bid ->
-            (* Check the id *)
-            if bid = l then update ()
-            else super#visit_InactivatedMutBorrow env bid
-
-      method! visit_loan_content env lc =
-        match lc with
-        | V.SharedLoan (bids, sv) ->
-            (* Control the dive *)
-            if ek.enter_shared_loans then super#visit_SharedLoan env bids sv
-            else V.SharedLoan (bids, sv)
-        | V.MutLoan bid ->
-            (* Nothing specific to do *)
-            super#visit_MutLoan env bid
-
-      method! visit_abs env abs =
-        if ek.enter_abs then super#visit_abs env abs else abs
-    end
-  in
-
-  let ctx = obj#visit_eval_ctx () ctx in
-  (* Check that we updated at least one borrow *)
-  assert !r;
-  ctx
-
-(** Update an abstraction borrow content.
-
-    The borrow is referred to by a borrow id.
-
-    This is a helper function: it might break invariants.     
- *)
-let update_aborrow (ek : exploration_kind) (l : V.BorrowId.id) (nv : V.avalue)
-    (ctx : C.eval_ctx) : C.eval_ctx =
-  (* We use a reference to check that we update exactly one borrow: when updating
-   * inside values, we check we don't update more than one borrow. Then, upon
-   * returning we check that we updated at least once. *)
-  let r = ref false in
-  let update () : V.avalue =
-    assert (not !r);
-    r := true;
-    nv
-  in
-
-  let obj =
-    object
-      inherit [_] C.map_eval_ctx as super
-
-      method! visit_ABorrow env bc =
-        match bc with
-        | V.AMutBorrow (bid, av) ->
-            if bid = l then update ()
-            else V.ABorrow (super#visit_AMutBorrow env bid av)
-        | V.ASharedBorrow bid ->
-            if bid = l then update ()
-            else V.ABorrow (super#visit_ASharedBorrow env bid)
-        | V.AIgnoredMutBorrow av ->
-            V.ABorrow (super#visit_AIgnoredMutBorrow env av)
-        | V.AProjSharedBorrow asb ->
-            if borrow_in_asb l asb then update ()
-            else V.ABorrow (super#visit_AProjSharedBorrow env asb)
-
-      method! visit_abs env abs =
-        if ek.enter_abs then super#visit_abs env abs else abs
-    end
-  in
-
-  let ctx = obj#visit_eval_ctx () ctx in
-  (* Check that we updated at least one borrow *)
-  assert !r;
-  ctx
-
 (** TODO: move to InterpreterSymbolic or sth *)
 type symbolic_expansion =
   | SeConcrete of V.constant_value
@@ -633,47 +208,6 @@ type symbolic_expansion =
   | SeMutRef of V.BorrowId.id * V.symbolic_proj_comp
   | SeSharedRef of V.BorrowId.set_t * V.symbolic_proj_comp
 
-(** The following type identifies the relative position of expressions (in
-    particular borrows) in other expressions.
-    
-    For instance, it is used to control [end_borrow]: we usually only allow
-    to end "outer" borrows, unless we perform a drop.
-*)
-type inner_outer = Inner | Outer
-
-type borrow_ids = Borrows of V.BorrowId.Set.t | Borrow of V.BorrowId.id
-
-exception FoundBorrowIds of borrow_ids
-
-let update_if_none opt x = match opt with None -> Some x | _ -> opt
-
-(** Auxiliary function: see its usage in [end_borrow_get_borrow_in_value] *)
-let update_outer_borrows (io : inner_outer)
-    (outer : V.AbstractionId.id option * borrow_ids option) (x : borrow_ids) :
-    V.AbstractionId.id option * borrow_ids option =
-  match io with
-  | Inner ->
-      (* If we can end inner borrows, we don't keep track of the outer borrows *)
-      outer
-  | Outer ->
-      let abs, opt = outer in
-      (abs, update_if_none opt x)
-
-(** Return the first loan we find in a value *)
-let get_first_loan_in_value (v : V.typed_value) : V.loan_content option =
-  let obj =
-    object
-      inherit [_] V.iter_typed_value
-
-      method! visit_loan_content _ lc = raise (FoundLoanContent lc)
-    end
-  in
-  (* We use exceptions *)
-  try
-    obj#visit_typed_value () v;
-    None
-  with FoundLoanContent lc -> Some lc
-
 (** Check if two different projections intersect. This is necessary when
     giving a symbolic value to an abstraction: we need to check that
     the regions which are already ended inside the abstraction don't
@@ -786,13 +320,6 @@ let bottom_in_avalue (v : V.typed_avalue) (_abs_regions : T.RegionId.set_t) :
     false
   with Found -> true
 
-type outer_borrows_or_abs =
-  | OuterBorrows of borrow_ids
-  | OuterAbs of V.AbstractionId.id
-
-exception FoundOuter of outer_borrows_or_abs
-(** Utility exception *)
-
 (** Return true if a type is "primitively copyable".
   *
   * "primitively copyable" means that copying instances of this type doesn't
diff --git a/src/Invariants.ml b/src/Invariants.ml
index 364c14d0..05373d1b 100644
--- a/src/Invariants.ml
+++ b/src/Invariants.ml
@@ -9,6 +9,7 @@ module Subst = Substitute
 module A = CfimAst
 module L = Logging
 open InterpreterUtils
+open InterpreterBorrowsCore
 
 let debug_invariants : bool ref = ref false
 
diff --git a/src/TypesUtils.ml b/src/TypesUtils.ml
index c1f52120..878ac989 100644
--- a/src/TypesUtils.ml
+++ b/src/TypesUtils.ml
@@ -23,6 +23,26 @@ let ty_is_unit (ty : 'r ty) : bool =
 (** The unit type *)
 let mk_unit_ty : ety = Adt (Tuple, [], [])
 
+(** Deconstruct a type of the form `Box<T>` to retrieve the `T` inside *)
+let ty_get_box (box_ty : ety) : ety =
+  match box_ty with
+  | Adt (Assumed Box, [], [ boxed_ty ]) -> boxed_ty
+  | _ -> failwith "Not a boxed type"
+
+(** Deconstruct a type of the form `&T` or `&mut T` to retrieve the `T` (and
+    the borrow kind, etc.)
+ *)
+let ty_get_ref (ty : ety) : erased_region * ety * ref_kind =
+  match ty with
+  | Ref (r, ty, ref_kind) -> (r, ty, ref_kind)
+  | _ -> failwith "Not a ref type"
+
+let mk_ref_ty (r : 'r) (ty : 'r ty) (ref_kind : ref_kind) : 'r ty =
+  Ref (r, ty, ref_kind)
+
+(** Make a box type *)
+let mk_box_ty (ty : 'r ty) : 'r ty = Adt (Assumed Box, [], [ ty ])
+
 (** Check if a region is in a set of regions *)
 let region_in_set (r : RegionId.id region) (rset : RegionId.set_t) : bool =
   match r with Static -> false | Var id -> RegionId.Set.mem id rset
diff --git a/src/ValuesUtils.ml b/src/ValuesUtils.ml
index 488de15d..4a503a65 100644
--- a/src/ValuesUtils.ml
+++ b/src/ValuesUtils.ml
@@ -1,8 +1,14 @@
-module T = Types
 open TypesUtils
+open Types
 open Values
 
 let mk_unit_value : typed_value =
   { value = Adt { variant_id = None; field_values = [] }; ty = mk_unit_ty }
 
-let mk_typed_value (ty : T.ety) (value : value) : typed_value = { value; ty }
+let mk_typed_value (ty : ety) (value : value) : typed_value = { value; ty }
+
+(** Box a value *)
+let mk_box_value (v : typed_value) : typed_value =
+  let box_ty = mk_box_ty v.ty in
+  let box_v = Adt { variant_id = None; field_values = [ v ] } in
+  mk_typed_value box_ty box_v