path: root/src/Contexts.ml

open Types
open Values
open CfimAst
module V = Values

(** Some global counters.
 *
 * Note that those counters were initially stored in [eval_ctx] values,
 * but it proved better to make them global and stateful:
 * - when branching (and thus executing on several paths with different
 *   contexts) it is better to really have unique ids everywhere (and
 *   not have fresh ids shared by several contexts even though introduced
 *   after the branching) because at some point we might need to merge the
 *   different contexts
 * - also, it is a lot more convenient to not store those counters in contexts
 *   objects
 *)

let symbolic_value_id_counter, fresh_symbolic_value_id =
  SymbolicValueId.fresh_stateful_generator ()

let borrow_id_counter, fresh_borrow_id = BorrowId.fresh_stateful_generator ()

let region_id_counter, fresh_region_id = RegionId.fresh_stateful_generator ()

let abstraction_id_counter, fresh_abstraction_id =
  AbstractionId.fresh_stateful_generator ()

(** We shouldn't need to reset the global counters, but it might be good to
    to it from time to time, every time we evaluate/synthesize a function for
    instance.
    
    The reasons are manifold:
    - it might prevent the counters from overflowing (although this seems
      extremely unlikely - as a side node: we have overflow checks to make
      sure the synthesis doesn't get impacted by potential overflows)
    - most importantly, it allows to always manipulate low values, which
      is always a lot more readable when debugging
 *)
let reset_global_counters () =
  symbolic_value_id_counter := SymbolicValueId.generator_zero;
  borrow_id_counter := BorrowId.generator_zero;
  region_id_counter := RegionId.generator_zero;
  abstraction_id_counter := AbstractionId.generator_zero

type binder = {
  index : VarId.id;  (** Unique variable identifier *)
  name : string option;  (** Possible name *)
}
[@@deriving show]
(** A binder used in an environment, to map a variable to a value *)

(** Environment value: mapping from variable to value, abstraction (only
    used in symbolic mode) or stack frame delimiter.
    
    TODO: rename Var (-> Binding?)
 *)
type env_elem = Var of (binder[@opaque]) * typed_value | Abs of abs | Frame
[@@deriving
  show,
    visitors
      {
        name = "iter_env_elem";
        variety = "iter";
        ancestors = [ "iter_abs" ];
        nude = true (* Don't inherit [VisitorsRuntime.iter] *);
        concrete = true;
      },
    visitors
      {
        name = "map_env_elem";
        variety = "map";
        ancestors = [ "map_abs" ];
        nude = true (* Don't inherit [VisitorsRuntime.iter] *);
        concrete = true;
      }]

type env = env_elem list
[@@deriving
  show,
    visitors
      {
        name = "iter_env";
        variety = "iter";
        ancestors = [ "iter_env_elem" ];
        nude = true (* Don't inherit [VisitorsRuntime.iter] *);
        concrete = true;
      },
    visitors
      {
        name = "map_env";
        variety = "map";
        ancestors = [ "map_env_elem" ];
        nude = true (* Don't inherit [VisitorsRuntime.iter] *);
        concrete = true;
      }]

type interpreter_mode = ConcreteMode | SymbolicMode [@@deriving show]

type config = { mode : interpreter_mode; check_invariants : bool }
[@@deriving show]

type type_context = { type_defs : type_def list } [@@deriving show]

type eval_ctx = {
  type_context : type_context;
  fun_context : fun_def list;
  type_vars : type_var list;
  env : env;
  ended_regions : RegionId.set_t;
}
[@@deriving show]
(** Evaluation context *)

let lookup_type_var (ctx : eval_ctx) (vid : TypeVarId.id) : type_var =
  TypeVarId.nth ctx.type_vars vid

let ctx_lookup_binder (ctx : eval_ctx) (vid : VarId.id) : binder =
  (* TOOD: we might want to stop at the end of the frame *)
  let rec lookup env =
    match env with
    | [] ->
        raise (Invalid_argument ("Variable not found: " ^ VarId.to_string vid))
    | Var (var, _) :: env' -> if var.index = vid then var else lookup env'
    | (Abs _ | Frame) :: env' -> lookup env'
  in
  lookup ctx.env

let ctx_lookup_type_def (ctx : eval_ctx) (tid : TypeDefId.id) : type_def =
  TypeDefId.nth ctx.type_context.type_defs tid

let ctx_lookup_fun_def (ctx : eval_ctx) (fid : FunDefId.id) : fun_def =
  FunDefId.nth ctx.fun_context fid

(** Retrieve a variable's value in an environment *)
let env_lookup_var_value (env : env) (vid : VarId.id) : typed_value =
  (* We take care to stop at the end of current frame: different variables
     in different frames can have the same id!
  *)
  let rec lookup env =
    match env with
    | [] -> failwith "Unexpected"
    | Var (var, v) :: env' -> if var.index = vid then v else lookup env'
    | Abs _ :: env' -> lookup env'
    | Frame :: _ -> failwith "End of frame"
  in
  lookup env

(** Retrieve a variable's value in an evaluation context *)
let ctx_lookup_var_value (ctx : eval_ctx) (vid : VarId.id) : typed_value =
  env_lookup_var_value ctx.env vid

(** Update a variable's value in an environment

    This is a helper function: it can break invariants and doesn't perform
    any check.
*)
let env_update_var_value (env : env) (vid : VarId.id) (nv : typed_value) : env =
  (* We take care to stop at the end of current frame: different variables
     in different frames can have the same id!
  *)
  let rec update env =
    match env with
    | [] -> failwith "Unexpected"
    | Var (var, v) :: env' ->
        if var.index = vid then Var (var, nv) :: env'
        else Var (var, v) :: update env'
    | Abs abs :: env' -> Abs abs :: update env'
    | Frame :: _ -> failwith "End of frame"
  in
  update env

let var_to_binder (var : var) : binder = { index = var.index; name = var.name }

(** Update a variable's value in an evaluation context.

    This is a helper function: it can break invariants and doesn't perform
    any check.
*)
let ctx_update_var_value (ctx : eval_ctx) (vid : VarId.id) (nv : typed_value) :
    eval_ctx =
  { ctx with env = env_update_var_value ctx.env vid nv }

(** Push a variable in the context's environment.

    Checks that the pushed variable and its value have the same type (this
    is important).
*)
let ctx_push_var (ctx : eval_ctx) (var : var) (v : typed_value) : eval_ctx =
  assert (var.var_ty = v.ty);
  let bv = var_to_binder var in
  { ctx with env = Var (bv, v) :: ctx.env }

(** Push a list of variables.

    Checks that the pushed variables and their values have the same type (this
    is important).
*)
let ctx_push_vars (ctx : eval_ctx) (vars : (var * typed_value) list) : eval_ctx
    =
  assert (
    List.for_all
      (fun (var, (value : typed_value)) -> var.var_ty = value.ty)
      vars);
  let vars =
    List.map (fun (var, value) -> Var (var_to_binder var, value)) vars
  in
  let vars = List.rev vars in
  { ctx with env = List.append vars ctx.env }

let mk_bottom (ty : ety) : typed_value = { value = Bottom; ty }

(** Push an uninitialized variable (which thus maps to [Bottom]) *)
let ctx_push_uninitialized_var (ctx : eval_ctx) (var : var) : eval_ctx =
  ctx_push_var ctx var (mk_bottom var.var_ty)

(** Push a list of uninitialized variables (which thus map to [Bottom]) *)
let ctx_push_uninitialized_vars (ctx : eval_ctx) (vars : var list) : eval_ctx =
  let vars = List.map (fun v -> (v, mk_bottom v.var_ty)) vars in
  ctx_push_vars ctx vars

let env_lookup_abs (env : env) (abs_id : V.AbstractionId.id) : V.abs =
  let rec lookup env =
    match env with
    | [] -> failwith "Unexpected"
    | Var (_, _) :: env' -> lookup env'
    | Abs abs :: env' -> if abs.abs_id = abs_id then abs else lookup env'
    | Frame :: env' -> lookup env'
  in
  lookup env

let ctx_lookup_abs (ctx : eval_ctx) (abs_id : V.AbstractionId.id) : V.abs =
  env_lookup_abs ctx.env abs_id

(** Visitor to iterate over the values in the *current* frame *)
class ['self] iter_frame =
  object (self : 'self)
    inherit [_] V.iter_abs

    method visit_Var : 'acc -> binder -> typed_value -> unit =
      fun acc _vid v -> self#visit_typed_value acc v

    method visit_Abs : 'acc -> abs -> unit =
      fun acc abs -> self#visit_abs acc abs

    method visit_env_elem : 'acc -> env_elem -> unit =
      fun acc em ->
        match em with
        | Var (vid, v) -> self#visit_Var acc vid v
        | Abs abs -> self#visit_Abs acc abs
        | Frame -> failwith "Unreachable"

    method visit_env : 'acc -> env -> unit =
      fun acc env ->
        match env with
        | [] -> ()
        | Frame :: _ -> (* We stop here *) ()
        | em :: env ->
            self#visit_env_elem acc em;
            self#visit_env acc env
  end

(** Visitor to map over the values in the *current* frame *)
class ['self] map_frame_concrete =
  object (self : 'self)
    inherit [_] V.map_abs

    method visit_Var : 'acc -> binder -> typed_value -> env_elem =
      fun acc vid v ->
        let v = self#visit_typed_value acc v in
        Var (vid, v)

    method visit_Abs : 'acc -> abs -> env_elem =
      fun acc abs -> Abs (self#visit_abs acc abs)

    method visit_env_elem : 'acc -> env_elem -> env_elem =
      fun acc em ->
        match em with
        | Var (vid, v) -> self#visit_Var acc vid v
        | Abs abs -> self#visit_Abs acc abs
        | Frame -> failwith "Unreachable"

    method visit_env : 'acc -> env -> env =
      fun acc env ->
        match env with
        | [] -> []
        | Frame :: env -> (* We stop here *) Frame :: env
        | em :: env ->
            let em = self#visit_env_elem acc em in
            let env = self#visit_env acc env in
            em :: env
  end

(** Visitor to iterate over the values in a context *)
class ['self] iter_eval_ctx =
  object (_self : 'self)
    inherit [_] iter_env as super

    method visit_eval_ctx : 'acc -> eval_ctx -> unit =
      fun acc ctx -> super#visit_env acc ctx.env
  end

(** Visitor to map the values in a context *)
class ['self] map_eval_ctx =
  object (_self : 'self)
    inherit [_] map_env as super

    method visit_eval_ctx : 'acc -> eval_ctx -> eval_ctx =
      fun acc ctx ->
        let env = super#visit_env acc ctx.env in
        { ctx with env }
  end