path: root/src/Values.ml

open Identifiers
open Types

(* TODO: I often write "abstract" (value, borrow content, etc.) while I should
 * write "abstraction" (because those values are not abstract, they simply are
 * inside abstractions) *)

module VarId = IdGen ()

module BorrowId = IdGen ()

module SymbolicValueId = IdGen ()

module AbstractionId = IdGen ()

(** A variable *)

type big_int = Z.t

let big_int_of_yojson (json : Yojson.Safe.t) : (big_int, string) result =
  match json with
  | `Int i -> Ok (Z.of_int i)
  | `Intlit is -> Ok (Z.of_string is)
  | _ -> Error "not an integer or an integer literal"

let big_int_to_yojson (i : big_int) = `Intlit (Z.to_string i)

let pp_big_int (fmt : Format.formatter) (bi : big_int) : unit =
  Format.pp_print_string fmt (Z.to_string bi)

let show_big_int (bi : big_int) : string = Z.to_string bi

type scalar_value = { value : big_int; int_ty : integer_type } [@@deriving show]
(** A scalar value

    Note that we use unbounded integers everywhere.
    We then harcode the boundaries for the different types.
 *)

(** A constant value *)
type constant_value =
  | Scalar of scalar_value
  | Bool of bool
  | Char of char
  | String of string
[@@deriving show]

type symbolic_value = { sv_id : SymbolicValueId.id; sv_ty : rty }
[@@deriving show]
(** Symbolic value *)

type symbolic_proj_comp = {
  svalue : symbolic_value;  (** The symbolic value itself *)
  rset_ended : RegionId.set_t;
      (** The regions used in the symbolic value which have already ended *)
}
[@@deriving show]
(** A complementary projector over a symbolic value.
    
    "Complementary" stands for the fact that it is a projector over all the
    regions *but* the ones which are listed in the projector.
*)

(** Ancestor for iter visitor for [typed_value] *)
class ['self] iter_typed_value_base =
  object (self : 'self)
    inherit [_] VisitorsRuntime.iter

    method visit_constant_value : 'env -> constant_value -> unit = fun _ _ -> ()

    method visit_erased_region : 'env -> erased_region -> unit = fun _ _ -> ()

    method visit_symbolic_proj_comp : 'env -> symbolic_proj_comp -> unit =
      fun _ _ -> ()

    method visit_ety : 'env -> ety -> unit = fun _ _ -> ()
  end

(** Ancestor for map visitor for [typed_value] *)
class ['self] map_typed_value_base =
  object (self : 'self)
    inherit [_] VisitorsRuntime.map

    method visit_constant_value : 'env -> constant_value -> constant_value =
      fun _ cv -> cv

    method visit_erased_region : 'env -> erased_region -> erased_region =
      fun _ r -> r

    method visit_symbolic_proj_comp
        : 'env -> symbolic_proj_comp -> symbolic_proj_comp =
      fun _ sv -> sv

    method visit_ety : 'env -> ety -> ety = fun _ ty -> ty
  end

(** An untyped value, used in the environments *)
type value =
  | Concrete of constant_value  (** Concrete (non-symbolic) value *)
  | Adt of adt_value  (** Enumerations and structures *)
  | Bottom  (** No value (uninitialized or moved value) *)
  | Borrow of borrow_content  (** A borrowed value *)
  | Loan of loan_content  (** A loaned value *)
  | Symbolic of symbolic_proj_comp  (** Unknown (symbolic) value *)

and adt_value = {
  variant_id : (VariantId.id option[@opaque]);
  field_values : typed_value list;
}

and borrow_content =
  | SharedBorrow of (BorrowId.id[@opaque])  (** A shared value *)
  | MutBorrow of (BorrowId.id[@opaque]) * typed_value
      (** A mutably borrowed value *)
  | InactivatedMutBorrow of (BorrowId.id[@opaque])
      (** An inactivated mut borrow.

          This is used to model two-phase borrows. When evaluating a two-phase
          mutable borrow, we first introduce an inactivated borrow which behaves
          like a shared borrow, until the moment we actually *use* the borrow:
          at this point, we end all the other shared borrows (or inactivated borrows
          - though there shouldn't be any other inactivated borrows if the program
          is well typed) of this value and replace the inactivated borrow with a
          mutable borrow.
       *)

and loan_content =
  | SharedLoan of (BorrowId.set_t[@opaque]) * typed_value
  | MutLoan of (BorrowId.id[@opaque])

and typed_value = { value : value; ty : ety }
[@@deriving
  show,
    visitors
      {
        name = "iter_typed_value";
        variety = "iter";
        ancestors = [ "iter_typed_value_base" ];
        nude = true (* Don't inherit [VisitorsRuntime.iter] *);
        concrete = true;
      },
    visitors
      {
        name = "map_typed_value";
        variety = "map";
        ancestors = [ "map_typed_value_base" ];
        nude = true (* Don't inherit [VisitorsRuntime.iter] *);
        concrete = true;
      }]
(** "Regular" typed value (we map variables to typed values) *)

(** When giving shared borrows to functions (i.e., inserting shared borrows inside
    abstractions) we need to reborrow the shared values. When doing so, we lookup
    the shared values and apply some special projections to the shared value
    (until we can't go further, i.e., we find symbolic values which may get
    expanded upon reading them later), which don't generate avalues but
    sets of borrow ids and symbolic values.
    
    Note that as shared values can't get modified it is ok to forget the
    structure of the values we projected, and only keep the set of borrows
    (and symbolic values).
    
    TODO: we may actually need to remember the structure, in order to know
    which borrows are inside which other borrows...
*)
type abstract_shared_borrow =
  | AsbBorrow of (BorrowId.id[@opaque])
  | AsbProjReborrows of (symbolic_value[@opaque]) * (rty[@opaque])
[@@deriving show]

type abstract_shared_borrows = abstract_shared_borrow list
(** A set of abstract shared borrows *)

type aproj =
  | AProjLoans of symbolic_value
  | AProjBorrows of symbolic_value * rty
[@@deriving show]

type region = RegionVarId.id Types.region [@@deriving show]

(** Ancestor for iter visitor for [typed_avalue] *)
class ['self] iter_typed_avalue_base =
  object (self : 'self)
    inherit [_] iter_typed_value

    method visit_region : 'env -> region -> unit = fun _ _ -> ()

    method visit_aproj : 'env -> aproj -> unit = fun _ _ -> ()

    method visit_rty : 'env -> rty -> unit = fun _ _ -> ()
  end

(** Ancestor for MAP visitor for [typed_avalue] *)
class ['self] map_typed_avalue_base =
  object (self : 'self)
    inherit [_] map_typed_value

    method visit_region : 'env -> region -> region = fun _ r -> r

    method visit_aproj : 'env -> aproj -> aproj = fun _ p -> p

    method visit_rty : 'env -> rty -> rty = fun _ ty -> ty
  end

(** Abstraction values are used inside of abstractions to properly model
    borrowing relations introduced by function calls.

    When calling a function, we lose information about the borrow graph:
    part of it is thus "abstracted" away.
*)
type avalue =
  | AConcrete of constant_value
      (** Note that this case is not used in the projections to keep track of the
          borrow graph (because there are no borrows in "concrete" values!) but
          to correctly instantiate the backward functions (we may give back some
          values at different moments: we need to remember what those values were
          precisely). Also note that even though avalues and values are not the
          same, once values are projected to avalues, those avalues still have
          the structure of the original values (this is necessary, again, to
          correctly instantiate the backward functions)
       *)
  | AAdt of adt_avalue
  | ABottom
  | ALoan of aloan_content
  | ABorrow of aborrow_content
  | ASymbolic of aproj

and adt_avalue = {
  variant_id : (VariantId.id option[@opaque]);
  field_values : typed_avalue list;
}

(** A loan content as stored in an abstraction.

    Note that the children avalues are independent of the parent avalues.
    For instance, the child avalue contained in an [AMutLoan] will likely
    contain other, independent loans. We keep track of the hierarchy because
    we need it to properly instantiate the backward functions when generating
    the pure translation.
*)
and aloan_content =
  | AMutLoan of (BorrowId.id[@opaque]) * typed_avalue
  | ASharedLoan of (BorrowId.set_t[@opaque]) * typed_value * typed_avalue
  | AEndedMutLoan of { given_back : typed_avalue; child : typed_avalue }
      (** TODO: in the formalization, given_back was initially a typed value
       (not an avalue). It seems more consistent to use a value, especially
       because then the invariants about the borrows are simpler (otherwise,
       there may be borrow ids duplicated in the context, which is very
       annoying).
       I think the original idea was that using values would make it
       simple to instantiate the backward function (because projecting
       deconstructs a bit the values with which we feed the function).
    *)
  | AEndedSharedLoan of typed_value * typed_avalue
  | AIgnoredMutLoan of (BorrowId.id[@opaque]) * typed_avalue
  | AEndedIgnoredMutLoan of { given_back : typed_avalue; child : typed_avalue }
  | AProjSharedLoan of (abstract_shared_borrows[@opaque])
      (** A projected shared loan - TODO: remove? Does it make sense? Maybe
          I should rename that to AIgnoredSharedLoan... *)

(** Note that when a borrow content is ended, it is replaced by Bottom (while
    we need to track ended loans more precisely, especially because of their
    children values).

    Note that contrary to [aloan_content], here the children avalues are
    note independent of the parent avalues. For instance, a value
    `AMutBorrow (_, AMutBorrow (_, ...)` (ignoring the types) really is
    to be seen like a `mut_borrow ... (mut_borrow ...)`.
    
    TODO: be more precise about the ignored borrows (keep track of the borrow
    ids)?
*)
and aborrow_content =
  | AMutBorrow of (BorrowId.id[@opaque]) * typed_avalue
  | ASharedBorrow of (BorrowId.id[@opaque])
  | AIgnoredMutBorrow of typed_avalue
  | AProjSharedBorrow of (abstract_shared_borrows[@opaque])
      (** A projected shared borrow *)

(* TODO: we may want to merge this with typed_value - would prevent some issues
   when accessing fields... *)
and typed_avalue = { value : avalue; ty : rty }
[@@deriving
  show,
    visitors
      {
        name = "iter_typed_avalue";
        variety = "iter";
        ancestors = [ "iter_typed_avalue_base" ];
        nude = true (* Don't inherit [VisitorsRuntime.iter] *);
        concrete = true;
      },
    visitors
      {
        name = "map_typed_avalue";
        variety = "map";
        ancestors = [ "map_typed_avalue_base" ];
        nude = true (* Don't inherit [VisitorsRuntime.iter] *);
        concrete = true;
      }]

type abs = {
  abs_id : (AbstractionId.id[@opaque]);
  parents : (AbstractionId.set_t[@opaque]);  (** The parent abstractions *)
  acc_regions : (RegionId.set_t[@opaque]);
      (** Union of the regions owned by the (transitive) parent abstractions and
          by the current abstraction *)
  regions : (RegionId.set_t[@opaque]);  (** Regions owned by this abstraction *)
  avalues : typed_avalue list;  (** The values in this abstraction *)
}
[@@deriving
  show,
    visitors
      {
        name = "iter_abs";
        variety = "iter";
        ancestors = [ "iter_typed_avalue" ];
        nude = true (* Don't inherit [VisitorsRuntime.iter] *);
        concrete = true;
      },
    visitors
      {
        name = "map_abs";
        variety = "map";
        ancestors = [ "map_typed_avalue" ];
        nude = true (* Don't inherit [VisitorsRuntime.iter] *);
        concrete = true;
      }]
(** Abstractions model the parts in the borrow graph where the borrowing relations
    have been abstracted because of a function call.
    
    In order to model the relations between the borrows, we use "abstraction values",
    which are a special kind of value.
*)