Source file script_interpreter.ml

(*****************************************************************************)
(*                                                                           *)
(* Open Source License                                                       *)
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open Alpha_context
open Script
open Script_typed_ir
open Script_ir_translator

(* ---- Run-time errors -----------------------------------------------------*)

type execution_trace =
  (Script.location * Gas.t * (Script.expr * string option) list) list

type error += Reject of Script.location * Script.expr * execution_trace option
type error += Overflow of Script.location * execution_trace option
type error += Runtime_contract_error : Contract.t * Script.expr -> error
type error += Bad_contract_parameter of Contract.t (* `Permanent *)
type error += Cannot_serialize_log
type error += Cannot_serialize_failure
type error += Cannot_serialize_storage

let () =
  let open Data_encoding in
  let trace_encoding =
    (list @@ obj3
       (req "location" Script.location_encoding)
       (req "gas" Gas.encoding)
       (req "stack"
          (list
             (obj2
                (req "item" (Script.expr_encoding))
                (opt "annot" string))))) in
  (* Reject *)
  register_error_kind
    `Temporary
    ~id:"michelson_v1.script_rejected"
    ~title: "Script failed"
    ~description: "A FAILWITH instruction was reached"
    (obj3
       (req "location" Script.location_encoding)
       (req "with" Script.expr_encoding)
       (opt "trace" trace_encoding))
    (function Reject (loc, v, trace) -> Some (loc, v, trace) | _ -> None)
    (fun (loc, v, trace) -> Reject (loc, v, trace));
  (* Overflow *)
  register_error_kind
    `Temporary
    ~id:"michelson_v1.script_overflow"
    ~title: "Script failed (overflow error)"
    ~description: "A FAIL instruction was reached due to the detection of an overflow"
    (obj2
       (req "location" Script.location_encoding)
       (opt "trace" trace_encoding))
    (function Overflow (loc, trace) -> Some (loc, trace) | _ -> None)
    (fun (loc, trace) -> Overflow (loc, trace));
  (* Runtime contract error *)
  register_error_kind
    `Temporary
    ~id:"michelson_v1.runtime_error"
    ~title: "Script runtime error"
    ~description: "Toplevel error for all runtime script errors"
    (obj2
       (req "contract_handle" Contract.encoding)
       (req "contract_code" Script.expr_encoding))
    (function
      | Runtime_contract_error (contract, expr) ->
          Some (contract, expr)
      | _ -> None)
    (fun (contract, expr) ->
       Runtime_contract_error (contract, expr)) ;
  (* Bad contract parameter *)
  register_error_kind
    `Permanent
    ~id:"michelson_v1.bad_contract_parameter"
    ~title:"Contract supplied an invalid parameter"
    ~description:"Either no parameter was supplied to a contract with \
                  a non-unit parameter type, a non-unit parameter was \
                  passed to an account, or a parameter was supplied of \
                  the wrong type"
    Data_encoding.(obj1 (req "contract" Contract.encoding))
    (function Bad_contract_parameter c -> Some c | _ -> None)
    (fun c -> Bad_contract_parameter c) ;
  (* Cannot serialize log *)
  register_error_kind
    `Temporary
    ~id:"michelson_v1.cannot_serialize_log"
    ~title:"Not enough gas to serialize execution trace"
    ~description:"Execution trace with stacks was to big to be serialized with \
                  the provided gas"
    Data_encoding.empty
    (function Cannot_serialize_log -> Some () | _ -> None)
    (fun () -> Cannot_serialize_log) ;
  (* Cannot serialize failure *)
  register_error_kind
    `Temporary
    ~id:"michelson_v1.cannot_serialize_failure"
    ~title:"Not enough gas to serialize argument of FAILWITH"
    ~description:"Argument of FAILWITH was too big to be serialized with \
                  the provided gas"
    Data_encoding.empty
    (function Cannot_serialize_failure -> Some () | _ -> None)
    (fun () -> Cannot_serialize_failure) ;
  (* Cannot serialize storage *)
  register_error_kind
    `Temporary
    ~id:"michelson_v1.cannot_serialize_storage"
    ~title:"Not enough gas to serialize execution storage"
    ~description:"The returned storage was too big to be serialized with \
                  the provided gas"
    Data_encoding.empty
    (function Cannot_serialize_storage -> Some () | _ -> None)
    (fun () -> Cannot_serialize_storage)

(* ---- interpreter ---------------------------------------------------------*)

type 'tys stack =
  | Item : 'ty * 'rest stack -> ('ty * 'rest) stack
  | Empty : end_of_stack stack

let unparse_stack ctxt (stack, stack_ty) =
  (* We drop the gas limit as this function is only used for debugging/errors. *)
  let ctxt = Gas.set_unlimited ctxt in
  let rec unparse_stack
    : type a. a stack * a stack_ty -> (Script.expr * string option) list tzresult Lwt.t
    = function
      | Empty, Empty_t -> return_nil
      | Item (v, rest), Item_t (ty, rest_ty, annot) ->
          unparse_data ctxt Readable ty v >>=? fun (data, _ctxt) ->
          unparse_stack (rest, rest_ty) >>=? fun rest ->
          let annot = match Script_ir_annot.unparse_var_annot annot with
            | [] -> None
            | [ a ] -> Some a
            | _ -> assert false in
          let data = Micheline.strip_locations data in
          return ((data, annot) :: rest) in
  unparse_stack (stack, stack_ty)

module Interp_costs = Michelson_v1_gas.Cost_of.Interpreter

let rec interp_stack_prefix_preserving_operation : type fbef bef faft aft result .
  (fbef stack -> (faft stack * result) tzresult Lwt.t)
  -> (fbef, faft, bef, aft) stack_prefix_preservation_witness
  -> bef stack
  -> (aft stack * result) tzresult Lwt.t =
  fun f n stk ->
    match n,stk with
    | Prefix (Prefix (Prefix (Prefix (Prefix (Prefix (Prefix (Prefix (Prefix (Prefix (Prefix (Prefix (Prefix (Prefix (Prefix (Prefix n))))))))))))))),
      Item (v0, Item (v1, Item (v2, Item (v3, Item (v4, Item (v5, Item (v6, Item (v7, Item (v8, Item (v9, Item (va, Item (vb, Item (vc, Item (vd, Item (ve, Item (vf, rest)))))))))))))))) ->
        interp_stack_prefix_preserving_operation f n rest >>=? fun (rest', result) ->
        return (Item (v0, Item (v1, Item (v2, Item (v3, Item (v4, Item (v5, Item (v6, Item (v7, Item (v8, Item (v9, Item (va, Item (vb, Item (vc, Item (vd, Item (ve, Item (vf, rest')))))))))))))))), result)
    | Prefix (Prefix (Prefix (Prefix n))),
      Item (v0, Item (v1, Item (v2, Item (v3, rest)))) ->
        interp_stack_prefix_preserving_operation f n rest >>=? fun (rest', result) ->
        return (Item (v0, Item (v1, Item (v2, Item (v3, rest')))), result)
    | Prefix n, Item (v, rest) ->
        interp_stack_prefix_preserving_operation f n rest >>=? fun (rest', result) ->
        return (Item (v, rest'), result)
    | Rest, v -> f v

type step_constants =
  { source : Contract.t ;
    payer : Contract.t ;
    self : Contract.t ;
    amount : Tez.t ;
    chain_id : Chain_id.t }

let rec step
  : type b a.
    (?log: execution_trace ref ->
     context -> step_constants -> (b, a) descr -> b stack ->
     (a stack * context) tzresult Lwt.t) =
  fun ?log ctxt step_constants ({ instr ; loc ; _ } as descr) stack ->
    Lwt.return (Gas.consume ctxt Interp_costs.cycle) >>=? fun ctxt ->
    let logged_return : type a b.
      (b, a) descr ->
      a stack * context ->
      (a stack * context) tzresult Lwt.t =
      fun descr (ret, ctxt) ->
        match log with
        | None -> return (ret, ctxt)
        | Some log ->
            trace
              Cannot_serialize_log
              (unparse_stack ctxt (ret, descr.aft)) >>=? fun stack ->
            log := (descr.loc, Gas.level ctxt, stack) :: !log ;
            return (ret, ctxt) in
    let get_log (log : execution_trace ref option) =
      Option.map ~f:(fun l -> List.rev !l) log in
    let consume_gas_terop : type ret arg1 arg2 arg3 rest.
      (_ * (_ * (_ * rest)), ret * rest) descr ->
      ((arg1 -> arg2 -> arg3 -> ret) * arg1 * arg2 * arg3) ->
      (arg1 -> arg2 -> arg3 -> Gas.cost) ->
      rest stack ->
      ((ret * rest) stack * context) tzresult Lwt.t =
      fun descr (op, x1, x2, x3) cost_func rest ->
        Lwt.return (Gas.consume ctxt (cost_func x1 x2 x3)) >>=? fun ctxt ->
        logged_return descr (Item (op x1 x2 x3, rest), ctxt) in
    let consume_gas_binop : type ret arg1 arg2 rest.
      (_ * (_ * rest), ret * rest) descr ->
      ((arg1 -> arg2 -> ret) * arg1 * arg2) ->
      (arg1 -> arg2 -> Gas.cost) ->
      rest stack ->
      context ->
      ((ret * rest) stack * context) tzresult Lwt.t =
      fun descr (op, x1, x2) cost_func rest ctxt ->
        Lwt.return (Gas.consume ctxt (cost_func x1 x2)) >>=? fun ctxt ->
        logged_return descr (Item (op x1 x2, rest), ctxt) in
    let consume_gas_unop : type ret arg rest.
      (_ * rest, ret * rest) descr ->
      ((arg -> ret) * arg) ->
      (arg -> Gas.cost) ->
      rest stack ->
      context ->
      ((ret * rest) stack * context) tzresult Lwt.t =
      fun descr (op, arg) cost_func rest ctxt ->
        Lwt.return (Gas.consume ctxt (cost_func arg)) >>=? fun ctxt ->
        logged_return descr (Item (op arg, rest), ctxt) in
    let logged_return :
      a stack * context ->
      (a stack * context) tzresult Lwt.t =
      logged_return descr in
    match instr, stack with
    (* stack ops *)
    | Drop, Item (_, rest) ->
        Lwt.return (Gas.consume ctxt Interp_costs.stack_op) >>=? fun ctxt ->
        logged_return (rest, ctxt)
    | Dup, Item (v, rest) ->
        Lwt.return (Gas.consume ctxt Interp_costs.stack_op) >>=? fun ctxt ->
        logged_return (Item (v, Item (v, rest)), ctxt)
    | Swap, Item (vi, Item (vo, rest)) ->
        Lwt.return (Gas.consume ctxt Interp_costs.stack_op) >>=? fun ctxt ->
        logged_return (Item (vo, Item (vi, rest)), ctxt)
    | Const v, rest ->
        Lwt.return (Gas.consume ctxt Interp_costs.push) >>=? fun ctxt ->
        logged_return (Item (v, rest), ctxt)
    (* options *)
    | Cons_some, Item (v, rest) ->
        Lwt.return (Gas.consume ctxt Interp_costs.wrap) >>=? fun ctxt ->
        logged_return (Item (Some v, rest), ctxt)
    | Cons_none _, rest ->
        Lwt.return (Gas.consume ctxt Interp_costs.variant_no_data) >>=? fun ctxt ->
        logged_return (Item (None, rest), ctxt)
    | If_none (bt, _), Item (None, rest) ->
        Lwt.return (Gas.consume ctxt Interp_costs.branch) >>=? fun ctxt ->
        step ?log ctxt step_constants bt rest
    | If_none (_, bf), Item (Some v, rest) ->
        Lwt.return (Gas.consume ctxt Interp_costs.branch) >>=? fun ctxt ->
        step ?log ctxt step_constants bf (Item (v, rest))
    (* pairs *)
    | Cons_pair, Item (a, Item (b, rest)) ->
        Lwt.return (Gas.consume ctxt Interp_costs.pair) >>=? fun ctxt ->
        logged_return (Item ((a, b), rest), ctxt)
    (* Peephole optimization for UNPAIR *)
    | Seq ({instr=Dup;_},
           {instr=Seq ({instr=Car;_},
                       {instr=Seq ({instr=Dip {instr=Cdr}},
                                   {instr=Nop;_});_});_}),
      Item ((a, b), rest) ->
        Lwt.return (Gas.consume ctxt Interp_costs.pair_access) >>=? fun ctxt ->
        logged_return (Item (a, Item (b, rest)), ctxt)
    | Car, Item ((a, _), rest) ->
        Lwt.return (Gas.consume ctxt Interp_costs.pair_access) >>=? fun ctxt ->
        logged_return (Item (a, rest), ctxt)
    | Cdr, Item ((_, b), rest) ->
        Lwt.return (Gas.consume ctxt Interp_costs.pair_access) >>=? fun ctxt ->
        logged_return (Item (b, rest), ctxt)
    (* unions *)
    | Left, Item (v, rest) ->
        Lwt.return (Gas.consume ctxt Interp_costs.wrap) >>=? fun ctxt ->
        logged_return (Item (L v, rest), ctxt)
    | Right, Item (v, rest) ->
        Lwt.return (Gas.consume ctxt Interp_costs.wrap) >>=? fun ctxt ->
        logged_return (Item (R v, rest), ctxt)
    | If_left (bt, _), Item (L v, rest) ->
        Lwt.return (Gas.consume ctxt Interp_costs.branch) >>=? fun ctxt ->
        step ?log ctxt step_constants bt (Item (v, rest))
    | If_left (_, bf), Item (R v, rest) ->
        Lwt.return (Gas.consume ctxt Interp_costs.branch) >>=? fun ctxt ->
        step ?log ctxt step_constants bf (Item (v, rest))
    (* lists *)
    | Cons_list, Item (hd, Item (tl, rest)) ->
        Lwt.return (Gas.consume ctxt Interp_costs.cons) >>=? fun ctxt ->
        logged_return (Item (hd :: tl, rest), ctxt)
    | Nil, rest ->
        Lwt.return (Gas.consume ctxt Interp_costs.variant_no_data) >>=? fun ctxt ->
        logged_return (Item ([], rest), ctxt)
    | If_cons (_, bf), Item ([], rest) ->
        Lwt.return (Gas.consume ctxt Interp_costs.branch) >>=? fun ctxt ->
        step ?log ctxt step_constants bf rest
    | If_cons (bt, _), Item (hd :: tl, rest) ->
        Lwt.return (Gas.consume ctxt Interp_costs.branch) >>=? fun ctxt ->
        step ?log ctxt step_constants bt (Item (hd, Item (tl, rest)))
    | List_map body, Item (l, rest) ->
        let rec loop rest ctxt l acc =
          Lwt.return (Gas.consume ctxt Interp_costs.loop_map) >>=? fun ctxt ->
          match l with
          | [] -> return (Item (List.rev acc, rest), ctxt)
          | hd :: tl ->
              step ?log ctxt step_constants body (Item (hd, rest))
              >>=? fun (Item (hd, rest), ctxt) ->
              loop rest ctxt tl (hd :: acc)
        in loop rest ctxt l [] >>=? fun (res, ctxt) ->
        logged_return (res, ctxt)
    | List_size, Item (list, rest) ->
        Lwt.return
          (List.fold_left
             (fun acc _ ->
                acc >>? fun (size, ctxt) ->
                Gas.consume ctxt Interp_costs.loop_size >>? fun ctxt ->
                ok (size + 1 (* FIXME: overflow *), ctxt))
             (ok (0, ctxt)) list) >>=? fun (len, ctxt) ->
        logged_return (Item (Script_int.(abs (of_int len)), rest), ctxt)
    | List_iter body, Item (l, init) ->
        let rec loop ctxt l stack =
          Lwt.return (Gas.consume ctxt Interp_costs.loop_iter) >>=? fun ctxt ->
          match l with
          | [] -> return (stack, ctxt)
          | hd :: tl ->
              step ?log ctxt step_constants body (Item (hd, stack))
              >>=? fun (stack, ctxt) ->
              loop ctxt tl stack
        in loop ctxt l init >>=? fun (res, ctxt) ->
        logged_return (res, ctxt)
    (* sets *)
    | Empty_set t, rest ->
        Lwt.return (Gas.consume ctxt Interp_costs.empty_set) >>=? fun ctxt ->
        logged_return (Item (empty_set t, rest), ctxt)
    | Set_iter body, Item (set, init) ->
        Lwt.return (Gas.consume ctxt (Interp_costs.set_to_list set)) >>=? fun ctxt ->
        let l = List.rev (set_fold (fun e acc -> e :: acc) set []) in
        let rec loop ctxt l stack =
          Lwt.return (Gas.consume ctxt Interp_costs.loop_iter) >>=? fun ctxt ->
          match l with
          | [] -> return (stack, ctxt)
          | hd :: tl ->
              step ?log ctxt step_constants body (Item (hd, stack))
              >>=? fun (stack, ctxt) ->
              loop ctxt tl stack
        in loop ctxt l init >>=? fun (res, ctxt) ->
        logged_return (res, ctxt)
    | Set_mem, Item (v, Item (set, rest)) ->
        consume_gas_binop descr (set_mem, v, set) Interp_costs.set_mem rest ctxt
    | Set_update, Item (v, Item (presence, Item (set, rest))) ->
        consume_gas_terop descr (set_update, v, presence, set) Interp_costs.set_update rest
    | Set_size, Item (set, rest) ->
        consume_gas_unop descr (set_size, set) (fun _ -> Interp_costs.set_size) rest ctxt
    (* maps *)
    | Empty_map (t, _), rest ->
        Lwt.return (Gas.consume ctxt Interp_costs.empty_map) >>=? fun ctxt ->
        logged_return (Item (empty_map t, rest), ctxt)
    | Map_map body, Item (map, rest) ->
        Lwt.return (Gas.consume ctxt (Interp_costs.map_to_list map)) >>=? fun ctxt ->
        let l = List.rev (map_fold (fun k v acc -> (k, v) :: acc) map []) in
        let rec loop rest ctxt l acc =
          Lwt.return (Gas.consume ctxt Interp_costs.loop_map) >>=? fun ctxt ->
          match l with
          | [] -> return (acc, ctxt)
          | (k, _) as hd :: tl ->
              step ?log ctxt step_constants body (Item (hd, rest))
              >>=? fun (Item (hd, rest), ctxt) ->
              loop rest ctxt tl (map_update k (Some hd) acc)
        in loop rest ctxt l (empty_map (map_key_ty map)) >>=? fun (res, ctxt) ->
        logged_return (Item (res, rest), ctxt)
    | Map_iter body, Item (map, init) ->
        Lwt.return (Gas.consume ctxt (Interp_costs.map_to_list map)) >>=? fun ctxt ->
        let l = List.rev (map_fold (fun k v acc -> (k, v) :: acc) map []) in
        let rec loop ctxt l stack =
          Lwt.return (Gas.consume ctxt Interp_costs.loop_iter) >>=? fun ctxt ->
          match l with
          | [] -> return (stack, ctxt)
          | hd :: tl ->
              step ?log ctxt step_constants body (Item (hd, stack))
              >>=? fun (stack, ctxt) ->
              loop ctxt tl stack
        in loop ctxt l init >>=? fun (res, ctxt) ->
        logged_return (res, ctxt)
    | Map_mem, Item (v, Item (map, rest)) ->
        consume_gas_binop descr (map_mem, v, map) Interp_costs.map_mem rest ctxt
    | Map_get, Item (v, Item (map, rest)) ->
        consume_gas_binop descr (map_get, v, map) Interp_costs.map_get rest ctxt
    | Map_update, Item (k, Item (v, Item (map, rest))) ->
        consume_gas_terop descr (map_update, k, v, map) Interp_costs.map_update rest
    | Map_size, Item (map, rest) ->
        consume_gas_unop descr (map_size, map) (fun _ -> Interp_costs.map_size) rest ctxt
    (* Big map operations *)
    | Empty_big_map (tk, tv), rest ->
        Lwt.return (Gas.consume ctxt Interp_costs.empty_map) >>=? fun ctxt ->
        logged_return (Item (Script_ir_translator.empty_big_map tk tv, rest), ctxt)
    | Big_map_mem, Item (key, Item (map, rest)) ->
        Lwt.return (Gas.consume ctxt (Interp_costs.map_mem key map.diff)) >>=? fun ctxt ->
        Script_ir_translator.big_map_mem ctxt key map >>=? fun (res, ctxt) ->
        logged_return (Item (res, rest), ctxt)
    | Big_map_get, Item (key, Item (map, rest)) ->
        Lwt.return (Gas.consume ctxt (Interp_costs.map_get key map.diff)) >>=? fun ctxt ->
        Script_ir_translator.big_map_get ctxt key map >>=? fun (res, ctxt) ->
        logged_return (Item (res, rest), ctxt)
    | Big_map_update, Item (key, Item (maybe_value, Item (map, rest))) ->
        consume_gas_terop descr
          (Script_ir_translator.big_map_update, key, maybe_value, map)
          (fun k v m -> Interp_costs.map_update k (Some v) m.diff) rest
    (* timestamp operations *)
    | Add_seconds_to_timestamp, Item (n, Item (t, rest)) ->
        consume_gas_binop descr
          (Script_timestamp.add_delta, t, n)
          Interp_costs.add_timestamp rest ctxt
    | Add_timestamp_to_seconds, Item (t, Item (n, rest)) ->
        consume_gas_binop descr (Script_timestamp.add_delta, t, n)
          Interp_costs.add_timestamp rest ctxt
    | Sub_timestamp_seconds, Item (t, Item (s, rest)) ->
        consume_gas_binop descr (Script_timestamp.sub_delta, t, s)
          Interp_costs.sub_timestamp rest ctxt
    | Diff_timestamps, Item (t1, Item (t2, rest)) ->
        consume_gas_binop descr (Script_timestamp.diff, t1, t2)
          Interp_costs.diff_timestamps rest ctxt
    (* string operations *)
    | Concat_string_pair, Item (x, Item (y, rest)) ->
        Lwt.return (Gas.consume ctxt (Interp_costs.concat_string [x; y])) >>=? fun ctxt ->
        let s = String.concat "" [x; y] in
        logged_return (Item (s, rest), ctxt)
    | Concat_string, Item (ss, rest) ->
        Lwt.return (Gas.consume ctxt (Interp_costs.concat_string ss)) >>=? fun ctxt ->
        let s = String.concat "" ss in
        logged_return (Item (s, rest), ctxt)
    | Slice_string, Item (offset, Item (length, Item (s, rest))) ->
        let s_length = Z.of_int (String.length s) in
        let offset = Script_int.to_zint offset in
        let length = Script_int.to_zint length in
        if Compare.Z.(offset < s_length && Z.add offset length <= s_length) then
          Lwt.return (Gas.consume ctxt (Interp_costs.slice_string (Z.to_int length))) >>=? fun ctxt ->
          logged_return (Item (Some (String.sub s (Z.to_int offset) (Z.to_int length)), rest), ctxt)
        else
          Lwt.return (Gas.consume ctxt (Interp_costs.slice_string 0)) >>=? fun ctxt ->
          logged_return (Item (None, rest), ctxt)
    | String_size, Item (s, rest) ->
        Lwt.return (Gas.consume ctxt Interp_costs.push) >>=? fun ctxt ->
        logged_return (Item (Script_int.(abs (of_int (String.length s))), rest), ctxt)
    (* bytes operations *)
    | Concat_bytes_pair, Item (x, Item (y, rest)) ->
        Lwt.return (Gas.consume ctxt (Interp_costs.concat_bytes [x; y])) >>=? fun ctxt ->
        let s = MBytes.concat "" [x; y] in
        logged_return (Item (s, rest), ctxt)
    | Concat_bytes, Item (ss, rest) ->
        Lwt.return (Gas.consume ctxt (Interp_costs.concat_bytes ss)) >>=? fun ctxt ->
        let s = MBytes.concat "" ss in
        logged_return (Item (s, rest), ctxt)
    | Slice_bytes, Item (offset, Item (length, Item (s, rest))) ->
        let s_length = Z.of_int (MBytes.length s) in
        let offset = Script_int.to_zint offset in
        let length = Script_int.to_zint length in
        if Compare.Z.(offset < s_length && Z.add offset length <= s_length) then
          Lwt.return (Gas.consume ctxt (Interp_costs.slice_string (Z.to_int length))) >>=? fun ctxt ->
          logged_return (Item (Some (MBytes.sub s (Z.to_int offset) (Z.to_int length)), rest), ctxt)
        else
          Lwt.return (Gas.consume ctxt (Interp_costs.slice_string 0)) >>=? fun ctxt ->
          logged_return (Item (None, rest), ctxt)
    | Bytes_size, Item (s, rest) ->
        Lwt.return (Gas.consume ctxt Interp_costs.push) >>=? fun ctxt ->
        logged_return (Item (Script_int.(abs (of_int (MBytes.length s))), rest), ctxt)
    (* currency operations *)
    | Add_tez, Item (x, Item (y, rest)) ->
        Lwt.return (Gas.consume ctxt Interp_costs.int64_op) >>=? fun ctxt ->
        Lwt.return Tez.(x +? y) >>=? fun res ->
        logged_return (Item (res, rest), ctxt)
    | Sub_tez, Item (x, Item (y, rest)) ->
        Lwt.return (Gas.consume ctxt Interp_costs.int64_op) >>=? fun ctxt ->
        Lwt.return Tez.(x -? y) >>=? fun res ->
        logged_return (Item (res, rest), ctxt)
    | Mul_teznat, Item (x, Item (y, rest)) ->
        Lwt.return (Gas.consume ctxt Interp_costs.int64_op) >>=? fun ctxt ->
        Lwt.return (Gas.consume ctxt Interp_costs.z_to_int64) >>=? fun ctxt ->
        begin
          match Script_int.to_int64 y with
          | None -> fail (Overflow (loc, get_log log))
          | Some y ->
              Lwt.return Tez.(x *? y) >>=? fun res ->
              logged_return (Item (res, rest), ctxt)
        end
    | Mul_nattez, Item (y, Item (x, rest)) ->
        Lwt.return (Gas.consume ctxt Interp_costs.int64_op) >>=? fun ctxt ->
        Lwt.return (Gas.consume ctxt Interp_costs.z_to_int64) >>=? fun ctxt ->
        begin
          match Script_int.to_int64 y with
          | None -> fail (Overflow (loc, get_log log))
          | Some y ->
              Lwt.return Tez.(x *? y) >>=? fun res ->
              logged_return (Item (res, rest), ctxt)
        end
    (* boolean operations *)
    | Or, Item (x, Item (y, rest)) ->
        consume_gas_binop descr ((||), x, y) Interp_costs.bool_binop rest ctxt
    | And, Item (x, Item (y, rest)) ->
        consume_gas_binop descr ((&&), x, y) Interp_costs.bool_binop rest ctxt
    | Xor, Item (x, Item (y, rest)) ->
        consume_gas_binop descr (Compare.Bool.(<>), x, y) Interp_costs.bool_binop rest ctxt
    | Not, Item (x, rest) ->
        consume_gas_unop descr (not, x) Interp_costs.bool_unop rest ctxt
    (* integer operations *)
    | Is_nat, Item (x, rest) ->
        consume_gas_unop descr (Script_int.is_nat, x) Interp_costs.abs rest ctxt
    | Abs_int, Item (x, rest) ->
        consume_gas_unop descr (Script_int.abs, x) Interp_costs.abs rest ctxt
    | Int_nat, Item (x, rest) ->
        consume_gas_unop descr (Script_int.int, x) Interp_costs.int rest ctxt
    | Neg_int, Item (x, rest) ->
        consume_gas_unop descr (Script_int.neg, x) Interp_costs.neg rest ctxt
    | Neg_nat, Item (x, rest) ->
        consume_gas_unop descr (Script_int.neg, x) Interp_costs.neg rest ctxt
    | Add_intint, Item (x, Item (y, rest)) ->
        consume_gas_binop descr (Script_int.add, x, y) Interp_costs.add rest ctxt
    | Add_intnat, Item (x, Item (y, rest)) ->
        consume_gas_binop descr (Script_int.add, x, y) Interp_costs.add rest ctxt
    | Add_natint, Item (x, Item (y, rest)) ->
        consume_gas_binop descr (Script_int.add, x, y) Interp_costs.add rest ctxt
    | Add_natnat, Item (x, Item (y, rest)) ->
        consume_gas_binop descr (Script_int.add_n, x, y) Interp_costs.add rest ctxt
    | Sub_int, Item (x, Item (y, rest)) ->
        consume_gas_binop descr (Script_int.sub, x, y) Interp_costs.sub rest ctxt
    | Mul_intint, Item (x, Item (y, rest)) ->
        consume_gas_binop descr (Script_int.mul, x, y) Interp_costs.mul rest ctxt
    | Mul_intnat, Item (x, Item (y, rest)) ->
        consume_gas_binop descr (Script_int.mul, x, y) Interp_costs.mul rest ctxt
    | Mul_natint, Item (x, Item (y, rest)) ->
        consume_gas_binop descr (Script_int.mul, x, y) Interp_costs.mul rest ctxt
    | Mul_natnat, Item (x, Item (y, rest)) ->
        consume_gas_binop descr (Script_int.mul_n, x, y) Interp_costs.mul rest ctxt
    | Ediv_teznat, Item (x, Item (y, rest)) ->
        Lwt.return (Gas.consume ctxt Interp_costs.int64_to_z) >>=? fun ctxt ->
        let x = Script_int.of_int64 (Tez.to_mutez x) in
        consume_gas_binop descr
          ((fun x y ->
              match Script_int.ediv x y with
              | None -> None
              | Some (q, r) ->
                  match Script_int.to_int64 q,
                        Script_int.to_int64 r with
                  | Some q, Some r ->
                      begin
                        match Tez.of_mutez q, Tez.of_mutez r with
                        | Some q, Some r -> Some (q,r)
                        (* Cannot overflow *)
                        | _ -> assert false
                      end
                  (* Cannot overflow *)
                  | _ -> assert false),
           x, y)
          Interp_costs.div
          rest
          ctxt
    | Ediv_tez, Item (x, Item (y, rest)) ->
        Lwt.return (Gas.consume ctxt Interp_costs.int64_to_z) >>=? fun ctxt ->
        Lwt.return (Gas.consume ctxt Interp_costs.int64_to_z) >>=? fun ctxt ->
        let x = Script_int.abs (Script_int.of_int64 (Tez.to_mutez x)) in
        let y = Script_int.abs (Script_int.of_int64 (Tez.to_mutez y)) in
        consume_gas_binop descr
          ((fun x y -> match Script_int.ediv_n x y with
              | None -> None
              | Some (q, r) ->
                  match Script_int.to_int64 r with
                  | None -> assert false (* Cannot overflow *)
                  | Some r ->
                      match Tez.of_mutez r with
                      | None -> assert false (* Cannot overflow *)
                      | Some r -> Some (q, r)),
           x, y)
          Interp_costs.div
          rest
          ctxt
    | Ediv_intint, Item (x, Item (y, rest)) ->
        consume_gas_binop descr (Script_int.ediv, x, y) Interp_costs.div rest ctxt
    | Ediv_intnat, Item (x, Item (y, rest)) ->
        consume_gas_binop descr (Script_int.ediv, x, y) Interp_costs.div rest ctxt
    | Ediv_natint, Item (x, Item (y, rest)) ->
        consume_gas_binop descr (Script_int.ediv, x, y) Interp_costs.div rest ctxt
    | Ediv_natnat, Item (x, Item (y, rest)) ->
        consume_gas_binop descr (Script_int.ediv_n, x, y) Interp_costs.div rest ctxt
    | Lsl_nat, Item (x, Item (y, rest)) ->
        Lwt.return (Gas.consume ctxt (Interp_costs.shift_left x y)) >>=? fun ctxt ->
        begin
          match Script_int.shift_left_n x y with
          | None -> fail (Overflow (loc, get_log log))
          | Some x -> logged_return (Item (x, rest), ctxt)
        end
    | Lsr_nat, Item (x, Item (y, rest)) ->
        Lwt.return (Gas.consume ctxt (Interp_costs.shift_right x y)) >>=? fun ctxt ->
        begin
          match Script_int.shift_right_n x y with
          | None -> fail (Overflow (loc, get_log log))
          | Some r -> logged_return (Item (r, rest), ctxt)
        end
    | Or_nat, Item (x, Item (y, rest)) ->
        consume_gas_binop descr (Script_int.logor, x, y) Interp_costs.logor rest ctxt
    | And_nat, Item (x, Item (y, rest)) ->
        consume_gas_binop descr (Script_int.logand, x, y) Interp_costs.logand rest ctxt
    | And_int_nat, Item (x, Item (y, rest)) ->
        consume_gas_binop descr (Script_int.logand, x, y) Interp_costs.logand rest ctxt
    | Xor_nat, Item (x, Item (y, rest)) ->
        consume_gas_binop descr (Script_int.logxor, x, y) Interp_costs.logxor rest ctxt
    | Not_int, Item (x, rest) ->
        consume_gas_unop descr (Script_int.lognot, x) Interp_costs.lognot rest ctxt
    | Not_nat, Item (x, rest) ->
        consume_gas_unop descr (Script_int.lognot, x) Interp_costs.lognot rest ctxt
    (* control *)
    | Seq (hd, tl), stack ->
        step ?log ctxt step_constants hd stack >>=? fun (trans, ctxt) ->
        step ?log ctxt step_constants tl trans
    | If (bt, _), Item (true, rest) ->
        Lwt.return (Gas.consume ctxt Interp_costs.branch) >>=? fun ctxt ->
        step ?log ctxt step_constants bt rest
    | If (_, bf), Item (false, rest) ->
        Lwt.return (Gas.consume ctxt Interp_costs.branch) >>=? fun ctxt ->
        step ?log ctxt step_constants bf rest
    | Loop body, Item (true, rest) ->
        Lwt.return (Gas.consume ctxt Interp_costs.loop_cycle) >>=? fun ctxt ->
        step ?log ctxt step_constants body rest >>=? fun (trans, ctxt) ->
        step ?log ctxt step_constants descr trans
    | Loop _, Item (false, rest) ->
        logged_return (rest, ctxt)
    | Loop_left body, Item (L v, rest) ->
        Lwt.return (Gas.consume ctxt Interp_costs.loop_cycle) >>=? fun ctxt ->
        step ?log ctxt step_constants body (Item (v, rest)) >>=? fun (trans, ctxt) ->
        step ?log ctxt step_constants descr trans
    | Loop_left _, Item (R v, rest) ->
        Lwt.return (Gas.consume ctxt Interp_costs.loop_cycle) >>=? fun ctxt ->
        logged_return (Item (v, rest), ctxt)
    | Dip b, Item (ign, rest) ->
        Lwt.return (Gas.consume ctxt Interp_costs.stack_op) >>=? fun ctxt ->
        step ?log ctxt step_constants b rest >>=? fun (res, ctxt) ->
        logged_return (Item (ign, res), ctxt)
    | Exec, Item (arg, Item (lam, rest)) ->
        Lwt.return (Gas.consume ctxt Interp_costs.exec) >>=? fun ctxt ->
        interp ?log ctxt step_constants lam arg >>=? fun (res, ctxt) ->
        logged_return (Item (res, rest), ctxt)
    | Apply capture_ty, Item (capture, Item (lam, rest)) -> (
        Lwt.return (Gas.consume ctxt Interp_costs.apply) >>=? fun ctxt ->
        let (Lam (descr, expr)) = lam in
        let (Item_t (full_arg_ty , _ , _)) = descr.bef in
        unparse_data ctxt Optimized capture_ty capture >>=? fun (const_expr, ctxt) ->
        unparse_ty ctxt capture_ty >>=? fun (ty_expr, ctxt) ->
        match full_arg_ty with
        | Pair_t ((capture_ty, _, _), (arg_ty, _, _), _, _) -> (
            let arg_stack_ty = Item_t (arg_ty, Empty_t, None) in
            let const_descr = ({
                loc = descr.loc ;
                bef = arg_stack_ty ;
                aft = Item_t (capture_ty, arg_stack_ty, None) ;
                instr = Const capture ;
              } : (_, _) descr) in
            let pair_descr = ({
                loc = descr.loc ;
                bef = Item_t (capture_ty, arg_stack_ty, None) ;
                aft = Item_t (full_arg_ty, Empty_t, None) ;
                instr = Cons_pair ;
              } : (_, _) descr) in
            let seq_descr = ({
                loc = descr.loc ;
                bef = arg_stack_ty ;
                aft = Item_t (full_arg_ty, Empty_t, None) ;
                instr = Seq (const_descr, pair_descr) ;
              } : (_, _) descr) in
            let full_descr = ({
                loc = descr.loc ;
                bef = arg_stack_ty ;
                aft = descr.aft ;
                instr = Seq (seq_descr, descr) ;
              } : (_, _) descr) in
            let full_expr = Micheline.Seq (0, [
                Prim (0, I_PUSH, [ ty_expr ; const_expr ], []) ;
                Prim (0, I_PAIR, [], []) ;
                expr ]) in
            let lam' = Lam (full_descr, full_expr) in
            logged_return (Item (lam', rest), ctxt)
          )
        | _ -> assert false
      )
    | Lambda lam, rest ->
        Lwt.return (Gas.consume ctxt Interp_costs.push) >>=? fun ctxt ->
        logged_return (Item (lam, rest), ctxt)
    | Failwith tv, Item (v, _) ->
        trace Cannot_serialize_failure
          (unparse_data ctxt Optimized tv v) >>=? fun (v, _ctxt) ->
        let v = Micheline.strip_locations v in
        fail (Reject (loc, v, get_log log))
    | Nop, stack ->
        logged_return (stack, ctxt)
    (* comparison *)
    | Compare ty, Item (a, Item (b, rest)) ->
        Lwt.return (Gas.consume ctxt (Interp_costs.compare ty a b)) >>=? fun ctxt ->
        logged_return (Item (Script_int.of_int @@ Script_ir_translator.compare_comparable ty a b, rest), ctxt)
    (* comparators *)
    | Eq, Item (cmpres, rest) ->
        let cmpres = Script_int.compare cmpres Script_int.zero in
        let cmpres = Compare.Int.(cmpres = 0) in
        Lwt.return (Gas.consume ctxt Interp_costs.compare_res) >>=? fun ctxt ->
        logged_return (Item (cmpres, rest), ctxt)
    | Neq, Item (cmpres, rest) ->
        let cmpres = Script_int.compare cmpres Script_int.zero in
        let cmpres = Compare.Int.(cmpres <> 0) in
        Lwt.return (Gas.consume ctxt Interp_costs.compare_res) >>=? fun ctxt ->
        logged_return (Item (cmpres, rest), ctxt)
    | Lt, Item (cmpres, rest) ->
        let cmpres = Script_int.compare cmpres Script_int.zero in
        let cmpres = Compare.Int.(cmpres < 0) in
        Lwt.return (Gas.consume ctxt Interp_costs.compare_res) >>=? fun ctxt ->
        logged_return (Item (cmpres, rest), ctxt)
    | Le, Item (cmpres, rest) ->
        let cmpres = Script_int.compare cmpres Script_int.zero in
        let cmpres = Compare.Int.(cmpres <= 0) in
        Lwt.return (Gas.consume ctxt Interp_costs.compare_res) >>=? fun ctxt ->
        logged_return (Item (cmpres, rest), ctxt)
    | Gt, Item (cmpres, rest) ->
        let cmpres = Script_int.compare cmpres Script_int.zero in
        let cmpres = Compare.Int.(cmpres > 0) in
        Lwt.return (Gas.consume ctxt Interp_costs.compare_res) >>=? fun ctxt ->
        logged_return (Item (cmpres, rest), ctxt)
    | Ge, Item (cmpres, rest) ->
        let cmpres = Script_int.compare cmpres Script_int.zero in
        let cmpres = Compare.Int.(cmpres >= 0) in
        Lwt.return (Gas.consume ctxt Interp_costs.compare_res) >>=? fun ctxt ->
        logged_return (Item (cmpres, rest), ctxt)
    (* packing *)
    | Pack t, Item (value, rest) ->
        Script_ir_translator.pack_data ctxt t value >>=? fun (bytes, ctxt) ->
        logged_return (Item (bytes, rest), ctxt)
    | Unpack t, Item (bytes, rest) ->
        Lwt.return (Gas.check_enough ctxt (Script.serialized_cost bytes)) >>=? fun () ->
        if Compare.Int.(MBytes.length bytes >= 1) &&
           Compare.Int.(MBytes.get_uint8 bytes 0 = 0x05) then
          let bytes = MBytes.sub bytes 1 (MBytes.length bytes - 1) in
          match Data_encoding.Binary.of_bytes Script.expr_encoding bytes with
          | None ->
              Lwt.return (Gas.consume ctxt (Interp_costs.unpack_failed bytes)) >>=? fun ctxt ->
              logged_return (Item (None, rest), ctxt)
          | Some expr ->
              Lwt.return (Gas.consume ctxt (Script.deserialized_cost expr)) >>=? fun ctxt ->
              parse_data ctxt ~legacy:false t (Micheline.root expr) >>= function
              | Ok (value, ctxt) ->
                  logged_return (Item (Some value, rest), ctxt)
              | Error _ignored ->
                  Lwt.return (Gas.consume ctxt (Interp_costs.unpack_failed bytes)) >>=? fun ctxt ->
                  logged_return (Item (None, rest), ctxt)
        else
          logged_return (Item (None, rest), ctxt)
    (* protocol *)
    | Address, Item ((_, address), rest) ->
        Lwt.return (Gas.consume ctxt Interp_costs.address) >>=? fun ctxt ->
        logged_return (Item (address, rest), ctxt)
    | Contract (t, entrypoint), Item (contract, rest) ->
        Lwt.return (Gas.consume ctxt Interp_costs.contract) >>=? fun ctxt ->
        begin match contract, entrypoint with
          | (contract, "default"), entrypoint | (contract, entrypoint), "default" ->
              Script_ir_translator.parse_contract_for_script
                ~legacy:false ctxt loc t contract ~entrypoint >>=? fun (ctxt, maybe_contract) ->
              logged_return (Item (maybe_contract, rest), ctxt)
          | _ -> logged_return (Item (None, rest), ctxt)
        end
    | Transfer_tokens,
      Item (p, Item (amount, Item ((tp, (destination, entrypoint)), rest))) ->
        Lwt.return (Gas.consume ctxt Interp_costs.transfer) >>=? fun ctxt ->
        collect_big_maps ctxt tp p >>=? fun (to_duplicate, ctxt) ->
        let to_update = no_big_map_id in
        extract_big_map_diff ctxt Optimized tp p
          ~to_duplicate ~to_update ~temporary:true >>=? fun (p, big_map_diff, ctxt) ->
        unparse_data ctxt Optimized tp p >>=? fun (p, ctxt) ->
        let operation =
          Transaction
            { amount ; destination ; entrypoint ;
              parameters = Script.lazy_expr (Micheline.strip_locations p) } in
        Lwt.return (fresh_internal_nonce ctxt) >>=? fun (ctxt, nonce) ->
        logged_return (Item ((Internal_operation { source = step_constants.self ; operation ; nonce }, big_map_diff), rest), ctxt)
    | Create_account,
      Item (manager, Item (delegate, Item (_delegatable, Item (credit, rest)))) ->
        Lwt.return (Gas.consume ctxt Interp_costs.create_account) >>=? fun ctxt ->
        Contract.fresh_contract_from_current_nonce ctxt >>=? fun (ctxt, contract) ->
        (* store in optimized binary representation - as unparsed with [Optimized]. *)
        let manager_bytes =
          Data_encoding.Binary.to_bytes_exn Signature.Public_key_hash.encoding manager in
        let storage =
          Script_repr.lazy_expr @@ Micheline.strip_locations @@
          Micheline.Bytes (0, manager_bytes) in
        let script =
          { code = Legacy_support.manager_script_code ;
            storage ;
          } in
        let operation =
          Origination
            { credit ; delegate ; preorigination = Some contract ; script } in
        Lwt.return (fresh_internal_nonce ctxt) >>=? fun (ctxt, nonce) ->
        logged_return (Item ((Internal_operation { source = step_constants.self ; operation ; nonce }, None),
                             Item ((contract, "default"), rest)), ctxt)
    | Implicit_account, Item (key, rest) ->
        Lwt.return (Gas.consume ctxt Interp_costs.implicit_account) >>=? fun ctxt ->
        let contract = Contract.implicit_contract key in
        logged_return (Item ((Unit_t None, (contract, "default")), rest), ctxt)
    | Create_contract (storage_type, param_type, Lam (_, code), root_name),
      Item (manager, Item
              (delegate, Item
                 (spendable, Item
                    (delegatable, Item
                       (credit, Item
                          (init, rest)))))) ->
        Lwt.return (Gas.consume ctxt Interp_costs.create_contract) >>=? fun ctxt ->
        unparse_ty ctxt param_type >>=? fun (unparsed_param_type, ctxt) ->
        let unparsed_param_type =
          Script_ir_translator.add_field_annot (Option.map ~f:(fun n -> `Field_annot n) root_name) None unparsed_param_type in
        unparse_ty ctxt storage_type >>=? fun (unparsed_storage_type, ctxt) ->
        let code =
          Script.lazy_expr @@
          Micheline.strip_locations
            (Seq (0, [ Prim (0, K_parameter, [ unparsed_param_type ], []) ;
                       Prim (0, K_storage, [ unparsed_storage_type ], []) ;
                       Prim (0, K_code, [ code ], []) ])) in
        collect_big_maps ctxt storage_type init >>=? fun (to_duplicate, ctxt) ->
        let to_update = no_big_map_id in
        extract_big_map_diff ctxt Optimized storage_type init
          ~to_duplicate ~to_update ~temporary:true >>=? fun (init, big_map_diff, ctxt) ->
        unparse_data ctxt Optimized storage_type init >>=? fun (storage, ctxt) ->
        let storage = Script.lazy_expr @@ Micheline.strip_locations storage in
        begin
          if spendable then
            Legacy_support.add_do ~manager_pkh:manager
              ~script_code:code ~script_storage:storage
          else if delegatable then
            Legacy_support.add_set_delegate ~manager_pkh:manager
              ~script_code:code ~script_storage:storage
          else if Legacy_support.has_default_entrypoint code then
            Legacy_support.add_root_entrypoint code >>=? fun code ->
            return (code, storage)
          else return (code, storage)
        end >>=? fun (code, storage) ->
        Contract.fresh_contract_from_current_nonce ctxt >>=? fun (ctxt, contract) ->
        let operation =
          Origination
            { credit ; delegate ; preorigination = Some contract ;
              script = { code ; storage } } in
        Lwt.return (fresh_internal_nonce ctxt) >>=? fun (ctxt, nonce) ->
        logged_return
          (Item ((Internal_operation { source = step_constants.self ; operation ; nonce }, big_map_diff),
                 Item ((contract, "default"), rest)), ctxt)
    | Create_contract_2 (storage_type, param_type, Lam (_, code), root_name),
      (* Removed the instruction's arguments manager, spendable and delegatable *)
      Item (delegate, Item
              (credit, Item
                 (init, rest))) ->
        Lwt.return (Gas.consume ctxt Interp_costs.create_contract) >>=? fun ctxt ->
        unparse_ty ctxt param_type >>=? fun (unparsed_param_type, ctxt) ->
        let unparsed_param_type =
          Script_ir_translator.add_field_annot (Option.map ~f:(fun n -> `Field_annot n) root_name) None unparsed_param_type in
        unparse_ty ctxt storage_type >>=? fun (unparsed_storage_type, ctxt) ->
        let code =
          Micheline.strip_locations
            (Seq (0, [ Prim (0, K_parameter, [ unparsed_param_type ], []) ;
                       Prim (0, K_storage, [ unparsed_storage_type ], []) ;
                       Prim (0, K_code, [ code ], []) ])) in
        collect_big_maps ctxt storage_type init >>=? fun (to_duplicate, ctxt) ->
        let to_update = no_big_map_id in
        extract_big_map_diff ctxt Optimized storage_type init
          ~to_duplicate ~to_update ~temporary:true >>=? fun (init, big_map_diff, ctxt) ->
        unparse_data ctxt Optimized storage_type init >>=? fun (storage, ctxt) ->
        let storage = Micheline.strip_locations storage in
        Contract.fresh_contract_from_current_nonce ctxt >>=? fun (ctxt, contract) ->
        let operation =
          Origination
            { credit ; delegate ; preorigination = Some contract ;
              script = { code = Script.lazy_expr code ;
                         storage = Script.lazy_expr storage } } in
        Lwt.return (fresh_internal_nonce ctxt) >>=? fun (ctxt, nonce) ->
        logged_return
          (Item ((Internal_operation { source = step_constants.self ; operation ; nonce }, big_map_diff),
                 Item ((contract, "default"), rest)), ctxt)
    | Set_delegate,
      Item (delegate, rest) ->
        Lwt.return (Gas.consume ctxt Interp_costs.create_account) >>=? fun ctxt ->
        let operation = Delegation delegate in
        Lwt.return (fresh_internal_nonce ctxt) >>=? fun (ctxt, nonce) ->
        logged_return (Item ((Internal_operation { source = step_constants.self ; operation ; nonce }, None), rest), ctxt)
    | Balance, rest ->
        Lwt.return (Gas.consume ctxt Interp_costs.balance) >>=? fun ctxt ->
        Contract.get_balance ctxt step_constants.self >>=? fun balance ->
        logged_return (Item (balance, rest), ctxt)
    | Now, rest ->
        Lwt.return (Gas.consume ctxt Interp_costs.now) >>=? fun ctxt ->
        let now = Script_timestamp.now ctxt in
        logged_return (Item (now, rest), ctxt)
    | Check_signature, Item (key, Item (signature, Item (message, rest))) ->
        Lwt.return (Gas.consume ctxt (Interp_costs.check_signature key message)) >>=? fun ctxt ->
        let res = Signature.check key signature message in
        logged_return (Item (res, rest), ctxt)
    | Hash_key, Item (key, rest) ->
        Lwt.return (Gas.consume ctxt Interp_costs.hash_key) >>=? fun ctxt ->
        logged_return (Item (Signature.Public_key.hash key, rest), ctxt)
    | Blake2b, Item (bytes, rest) ->
        Lwt.return (Gas.consume ctxt (Interp_costs.hash_blake2b bytes)) >>=? fun ctxt ->
        let hash = Raw_hashes.blake2b bytes in
        logged_return (Item (hash, rest), ctxt)
    | Sha256, Item (bytes, rest) ->
        Lwt.return (Gas.consume ctxt (Interp_costs.hash_sha256 bytes)) >>=? fun ctxt ->
        let hash = Raw_hashes.sha256 bytes in
        logged_return (Item (hash, rest), ctxt)
    | Sha512, Item (bytes, rest) ->
        Lwt.return (Gas.consume ctxt (Interp_costs.hash_sha512 bytes)) >>=? fun ctxt ->
        let hash = Raw_hashes.sha512 bytes in
        logged_return (Item (hash, rest), ctxt)
    | Steps_to_quota, rest ->
        Lwt.return (Gas.consume ctxt Interp_costs.steps_to_quota) >>=? fun ctxt ->
        let steps = match Gas.level ctxt with
          | Limited { remaining } -> remaining
          | Unaccounted -> Z.of_string "99999999" in
        logged_return (Item (Script_int.(abs (of_zint steps)), rest), ctxt)
    | Source, rest ->
        Lwt.return (Gas.consume ctxt Interp_costs.source) >>=? fun ctxt ->
        logged_return (Item ((step_constants.payer, "default"), rest), ctxt)
    | Sender, rest ->
        Lwt.return (Gas.consume ctxt Interp_costs.source) >>=? fun ctxt ->
        logged_return (Item ((step_constants.source, "default"), rest), ctxt)
    | Self (t, entrypoint), rest ->
        Lwt.return (Gas.consume ctxt Interp_costs.self) >>=? fun ctxt ->
        logged_return (Item ((t, (step_constants.self, entrypoint)), rest), ctxt)
    | Amount, rest ->
        Lwt.return (Gas.consume ctxt Interp_costs.amount) >>=? fun ctxt ->
        logged_return (Item (step_constants.amount, rest), ctxt)
    | Dig (n, n'), stack ->
        Lwt.return (Gas.consume ctxt (Interp_costs.stack_n_op n)) >>=? fun ctxt ->
        interp_stack_prefix_preserving_operation (fun (Item (v, rest)) -> return (rest, v)) n' stack
        >>=? fun (aft, x) -> logged_return (Item (x, aft), ctxt)
    | Dug (n, n'), Item (v, rest) ->
        Lwt.return (Gas.consume ctxt (Interp_costs.stack_n_op n)) >>=? fun ctxt ->
        interp_stack_prefix_preserving_operation (fun stk -> return (Item (v, stk), ())) n' rest
        >>=? fun (aft, ()) -> logged_return (aft, ctxt)
    | Dipn (n, n', b), stack ->
        Lwt.return (Gas.consume ctxt (Interp_costs.stack_n_op n)) >>=? fun ctxt ->
        interp_stack_prefix_preserving_operation (fun stk ->
            step ?log ctxt step_constants b stk >>=? fun (res, ctxt') ->
            return (res, ctxt')) n' stack
        >>=? fun (aft, ctxt') -> logged_return (aft, ctxt')
    | Dropn (n, n'), stack ->
        Lwt.return (Gas.consume ctxt (Interp_costs.stack_n_op n)) >>=? fun ctxt ->
        interp_stack_prefix_preserving_operation (fun stk -> return (stk, stk)) n' stack
        >>=? fun (_, rest) -> logged_return (rest, ctxt)
    | ChainId, rest ->
        Lwt.return (Gas.consume ctxt Interp_costs.chain_id) >>=? fun ctxt ->
        logged_return (Item (step_constants.chain_id, rest), ctxt)

and interp
  : type p r.
    (?log: execution_trace ref ->
     context ->
     step_constants -> (p, r) lambda -> p ->
     (r * context) tzresult Lwt.t)
  = fun ?log ctxt step_constants (Lam (code, _)) arg ->
    let stack = (Item (arg, Empty)) in
    begin match log with
      | None -> return_unit
      | Some log ->
          trace Cannot_serialize_log
            (unparse_stack ctxt (stack, code.bef)) >>=? fun stack ->
          log := (code.loc, Gas.level ctxt, stack) :: !log ;
          return_unit
    end >>=? fun () ->
    step ?log ctxt step_constants code stack >>=? fun (Item (ret, Empty), ctxt) ->
    return (ret, ctxt)

(* ---- contract handling ---------------------------------------------------*)

and execute ?log ctxt mode step_constants ~entrypoint unparsed_script arg :
  (Script.expr * packed_internal_operation list * context * Contract.big_map_diff option) tzresult Lwt.t =
  parse_script ctxt unparsed_script ~legacy:true
  >>=? fun (Ex_script { code ; arg_type ; storage ; storage_type ; root_name }, ctxt) ->
  trace
    (Bad_contract_parameter step_constants.self)
    (Lwt.return (find_entrypoint arg_type ~root_name entrypoint)) >>=? fun (box, _) ->
  trace
    (Bad_contract_parameter step_constants.self)
    (parse_data ctxt ~legacy:false arg_type (box arg))  >>=? fun (arg, ctxt) ->
  Script.force_decode ctxt unparsed_script.code >>=? fun (script_code, ctxt) ->
  Script_ir_translator.collect_big_maps ctxt arg_type arg >>=? fun (to_duplicate, ctxt) ->
  Script_ir_translator.collect_big_maps ctxt storage_type storage >>=? fun (to_update, ctxt) ->
  trace
    (Runtime_contract_error (step_constants.self, script_code))
    (interp ?log ctxt step_constants code (arg, storage))
  >>=? fun ((ops, storage), ctxt) ->
  Script_ir_translator.extract_big_map_diff ctxt mode
    ~temporary:false ~to_duplicate ~to_update storage_type storage
  >>=? fun (storage, big_map_diff, ctxt) ->
  trace Cannot_serialize_storage
    (unparse_data ctxt mode storage_type storage) >>=? fun (storage, ctxt) ->
  let ops, op_diffs = List.split ops in
  let big_map_diff = match
      List.flatten (List.map (Option.unopt ~default:[]) (op_diffs @ [ big_map_diff ]))
    with
    | [] -> None
    | diff -> Some diff in
  return (Micheline.strip_locations storage, ops, ctxt, big_map_diff)

type execution_result =
  { ctxt : context ;
    storage : Script.expr ;
    big_map_diff : Contract.big_map_diff option ;
    operations : packed_internal_operation list }

let trace ctxt mode step_constants ~script ~entrypoint ~parameter =
  let log = ref [] in
  execute ~log ctxt mode step_constants ~entrypoint script (Micheline.root parameter)
  >>=? fun (storage, operations, ctxt, big_map_diff) ->
  let trace = List.rev !log in
  return ({ ctxt ; storage ; big_map_diff ; operations }, trace)

let execute ctxt mode step_constants ~script ~entrypoint ~parameter =
  execute ctxt mode step_constants ~entrypoint script (Micheline.root parameter)
  >>=? fun (storage, operations, ctxt, big_map_diff) ->
  return { ctxt ; storage ; big_map_diff ; operations }