catala/compiler/dcalc/interpreter.ml

(* This file is part of the Catala compiler, a specification language for tax
   and social benefits computation rules. Copyright (C) 2020 Inria, contributor:
   Denis Merigoux <denis.merigoux@inria.fr>, Emile Rolley <emile.rolley@tuta.io>

   Licensed under the Apache License, Version 2.0 (the "License"); you may not
   use this file except in compliance with the License. You may obtain a copy of
   the License at

   http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
   WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
   License for the specific language governing permissions and limitations under
   the License. *)

(** Reference interpreter for the default calculus *)

open Catala_utils
open Shared_ast
module Runtime = Runtime_ocaml.Runtime

(** {1 Helpers} *)

let is_empty_error (e : 'm Ast.expr) : bool =
  match Marked.unmark e with ELit LEmptyError -> true | _ -> false

let log_indent = ref 0

(** {1 Evaluation} *)

let print_log ctx entry infos pos e =
  if !Cli.trace_flag then
    match entry with
    | VarDef _ ->
      (* TODO: this usage of Format is broken, Formatting requires that all is
         formatted in one pass, without going through intermediate "%s" *)
      Cli.log_format "%*s%a %a: %s" (!log_indent * 2) "" Print.log_entry entry
        Print.uid_list infos
        (match Marked.unmark e with
        | EAbs _ -> Cli.with_style [ANSITerminal.green] "<function>"
        | _ ->
          let expr_str =
            Format.asprintf "%a" (Expr.format ctx ~debug:false) e
          in
          let expr_str =
            Re.Pcre.substitute ~rex:(Re.Pcre.regexp "\n\\s*")
              ~subst:(fun _ -> " ")
              expr_str
          in
          Cli.with_style [ANSITerminal.green] "%s" expr_str)
    | PosRecordIfTrueBool -> (
      match pos <> Pos.no_pos, Marked.unmark e with
      | true, ELit (LBool true) ->
        Cli.log_format "%*s%a%s:\n%s" (!log_indent * 2) "" Print.log_entry entry
          (Cli.with_style [ANSITerminal.green] "Definition applied")
          (Cli.add_prefix_to_each_line (Pos.retrieve_loc_text pos) (fun _ ->
               Format.asprintf "%*s" (!log_indent * 2) ""))
      | _ -> ())
    | BeginCall ->
      Cli.log_format "%*s%a %a" (!log_indent * 2) "" Print.log_entry entry
        Print.uid_list infos;
      log_indent := !log_indent + 1
    | EndCall ->
      log_indent := !log_indent - 1;
      Cli.log_format "%*s%a %a" (!log_indent * 2) "" Print.log_entry entry
        Print.uid_list infos

(* Todo: this should be handled early when resolving overloads. Here we have
   proper structural equality, but the OCaml backend for example uses the
   builtin equality function instead of this. *)
let rec handle_eq ctx pos e1 e2 =
  let open Runtime.Oper in
  match e1, e2 with
  | ELit LUnit, ELit LUnit -> true
  | ELit (LBool b1), ELit (LBool b2) -> not (o_xor b1 b2)
  | ELit (LInt x1), ELit (LInt x2) -> o_eq_int_int x1 x2
  | ELit (LRat x1), ELit (LRat x2) -> o_eq_rat_rat x1 x2
  | ELit (LMoney x1), ELit (LMoney x2) -> o_eq_mon_mon x1 x2
  | ELit (LDuration x1), ELit (LDuration x2) -> o_eq_dur_dur x1 x2
  | ELit (LDate x1), ELit (LDate x2) -> o_eq_dat_dat x1 x2
  | EArray es1, EArray es2 -> (
    try
      List.for_all2
        (fun e1 e2 ->
          match evaluate_operator ctx Eq pos [e1; e2] with
          | ELit (LBool b) -> b
          | _ -> assert false
          (* should not happen *))
        es1 es2
    with Invalid_argument _ -> false)
  | EStruct { fields = es1; name = s1 }, EStruct { fields = es2; name = s2 } ->
    StructName.equal s1 s2
    && StructField.Map.equal
         (fun e1 e2 ->
           match evaluate_operator ctx Eq pos [e1; e2] with
           | ELit (LBool b) -> b
           | _ -> assert false
           (* should not happen *))
         es1 es2
  | ( EInj { e = e1; cons = i1; name = en1 },
      EInj { e = e2; cons = i2; name = en2 } ) -> (
    try
      EnumName.equal en1 en2
      && EnumConstructor.equal i1 i2
      &&
      match evaluate_operator ctx Eq pos [e1; e2] with
      | ELit (LBool b) -> b
      | _ -> assert false
      (* should not happen *)
    with Invalid_argument _ -> false)
  | _, _ -> false (* comparing anything else return false *)

(* Call-by-value: the arguments are expected to be already evaluated here *)
and evaluate_operator :
    type k.
    decl_ctx ->
    (dcalc, k) operator ->
    Pos.t ->
    'm Ast.expr list ->
    'm Ast.naked_expr =
 fun ctx op pos args ->
  let protect f x y =
    let get_binop_args_pos = function
      | (arg0 :: arg1 :: _ : 'm Ast.expr list) ->
        [None, Expr.pos arg0; None, Expr.pos arg1]
      | _ -> assert false
    in
    try f x y with
    | Division_by_zero ->
      Errors.raise_multispanned_error
        [
          Some "The division operator:", pos;
          Some "The null denominator:", Expr.pos (List.nth args 1);
        ]
        "division by zero at runtime"
    | Runtime.UncomparableDurations ->
      Errors.raise_multispanned_error (get_binop_args_pos args)
        "Cannot compare together durations that cannot be converted to a \
         precise number of days"
  in
  let err () =
    Errors.raise_multispanned_error
      ([Some "Operator:", pos]
      @ List.mapi
          (fun i arg ->
            ( Some
                (Format.asprintf "Argument n°%d, value %a" (i + 1)
                   (Expr.format ctx ~debug:true)
                   arg),
              Expr.pos arg ))
          args)
      "Operator applied to the wrong arguments\n\
       (should not happen if the term was well-typed)"
  in
  let open Runtime.Oper in
  if List.exists (function ELit LEmptyError, _ -> true | _ -> false) args then
    ELit LEmptyError
  else
    Operator.kind_dispatch op
      ~polymorphic:(fun op ->
        match op, args with
        | Length, [(EArray es, _)] ->
          ELit (LInt (Runtime.integer_of_int (List.length es)))
        | Log (entry, infos), [e'] ->
          print_log ctx entry infos pos e';
          Marked.unmark e'
        | Eq, [(e1, _); (e2, _)] -> ELit (LBool (handle_eq ctx pos e1 e2))
        | Map, [f; (EArray es, _)] ->
          EArray
            (List.map
               (fun e' ->
                 evaluate_expr ctx
                   (Marked.same_mark_as (EApp { f; args = [e'] }) e'))
               es)
        | Reduce, [_; default; (EArray [], _)] -> Marked.unmark default
        | Reduce, [f; _; (EArray (x0 :: xn), _)] ->
          Marked.unmark
            (List.fold_left
               (fun acc x ->
                 evaluate_expr ctx
                   (Marked.same_mark_as (EApp { f; args = [acc; x] }) f))
               x0 xn)
        | Concat, [(EArray es1, _); (EArray es2, _)] -> EArray (es1 @ es2)
        | Filter, [f; (EArray es, _)] ->
          EArray
            (List.filter
               (fun e' ->
                 match
                   evaluate_expr ctx
                     (Marked.same_mark_as (EApp { f; args = [e'] }) e')
                 with
                 | ELit (LBool b), _ -> b
                 | _ ->
                   Errors.raise_spanned_error
                     (Expr.pos (List.nth args 0))
                     "This predicate evaluated to something else than a \
                      boolean (should not happen if the term was well-typed)")
               es)
        | Fold, [f; init; (EArray es, _)] ->
          Marked.unmark
            (List.fold_left
               (fun acc e' ->
                 evaluate_expr ctx
                   (Marked.same_mark_as (EApp { f; args = [acc; e'] }) e'))
               init es)
        | (Length | Log _ | Eq | Map | Concat | Filter | Fold | Reduce), _ ->
          err ())
      ~monomorphic:(fun op ->
        let rlit =
          match op, List.map (function ELit l, _ -> l | _ -> err ()) args with
          | Not, [LBool b] -> LBool (o_not b)
          | GetDay, [LDate d] -> LInt (o_getDay d)
          | GetMonth, [LDate d] -> LInt (o_getMonth d)
          | GetYear, [LDate d] -> LInt (o_getYear d)
          | FirstDayOfMonth, [LDate d] -> LDate (o_firstDayOfMonth d)
          | LastDayOfMonth, [LDate d] -> LDate (o_lastDayOfMonth d)
          | And, [LBool b1; LBool b2] -> LBool (o_and b1 b2)
          | Or, [LBool b1; LBool b2] -> LBool (o_or b1 b2)
          | Xor, [LBool b1; LBool b2] -> LBool (o_xor b1 b2)
          | ( ( Not | GetDay | GetMonth | GetYear | FirstDayOfMonth
              | LastDayOfMonth | And | Or | Xor ),
              _ ) ->
            err ()
        in
        ELit rlit)
      ~resolved:(fun op ->
        let rlit =
          match op, List.map (function ELit l, _ -> l | _ -> err ()) args with
          | Minus_int, [LInt x] -> LInt (o_minus_int x)
          | Minus_rat, [LRat x] -> LRat (o_minus_rat x)
          | Minus_mon, [LMoney x] -> LMoney (o_minus_mon x)
          | Minus_dur, [LDuration x] -> LDuration (o_minus_dur x)
          | ToRat_int, [LInt i] -> LRat (o_torat_int i)
          | ToRat_mon, [LMoney i] -> LRat (o_torat_mon i)
          | ToMoney_rat, [LRat i] -> LMoney (o_tomoney_rat i)
          | Round_mon, [LMoney m] -> LMoney (o_round_mon m)
          | Round_rat, [LRat m] -> LRat (o_round_rat m)
          | Add_int_int, [LInt x; LInt y] -> LInt (o_add_int_int x y)
          | Add_rat_rat, [LRat x; LRat y] -> LRat (o_add_rat_rat x y)
          | Add_mon_mon, [LMoney x; LMoney y] -> LMoney (o_add_mon_mon x y)
          | Add_dat_dur, [LDate x; LDuration y] -> LDate (o_add_dat_dur x y)
          | Add_dur_dur, [LDuration x; LDuration y] ->
            LDuration (o_add_dur_dur x y)
          | Sub_int_int, [LInt x; LInt y] -> LInt (o_sub_int_int x y)
          | Sub_rat_rat, [LRat x; LRat y] -> LRat (o_sub_rat_rat x y)
          | Sub_mon_mon, [LMoney x; LMoney y] -> LMoney (o_sub_mon_mon x y)
          | Sub_dat_dat, [LDate x; LDate y] -> LDuration (o_sub_dat_dat x y)
          | Sub_dat_dur, [LDate x; LDuration y] -> LDate (o_sub_dat_dur x y)
          | Sub_dur_dur, [LDuration x; LDuration y] ->
            LDuration (o_sub_dur_dur x y)
          | Mult_int_int, [LInt x; LInt y] -> LInt (o_mult_int_int x y)
          | Mult_rat_rat, [LRat x; LRat y] -> LRat (o_mult_rat_rat x y)
          | Mult_mon_rat, [LMoney x; LRat y] -> LMoney (o_mult_mon_rat x y)
          | Mult_dur_int, [LDuration x; LInt y] ->
            LDuration (o_mult_dur_int x y)
          | Div_int_int, [LInt x; LInt y] -> LRat (protect o_div_int_int x y)
          | Div_rat_rat, [LRat x; LRat y] -> LRat (protect o_div_rat_rat x y)
          | Div_mon_mon, [LMoney x; LMoney y] ->
            LRat (protect o_div_mon_mon x y)
          | Div_mon_rat, [LMoney x; LRat y] ->
            LMoney (protect o_div_mon_rat x y)
          | Lt_int_int, [LInt x; LInt y] -> LBool (o_lt_int_int x y)
          | Lt_rat_rat, [LRat x; LRat y] -> LBool (o_lt_rat_rat x y)
          | Lt_mon_mon, [LMoney x; LMoney y] -> LBool (o_lt_mon_mon x y)
          | Lt_dat_dat, [LDate x; LDate y] -> LBool (o_lt_dat_dat x y)
          | Lt_dur_dur, [LDuration x; LDuration y] ->
            LBool (protect o_lt_dur_dur x y)
          | Lte_int_int, [LInt x; LInt y] -> LBool (o_lte_int_int x y)
          | Lte_rat_rat, [LRat x; LRat y] -> LBool (o_lte_rat_rat x y)
          | Lte_mon_mon, [LMoney x; LMoney y] -> LBool (o_lte_mon_mon x y)
          | Lte_dat_dat, [LDate x; LDate y] -> LBool (o_lte_dat_dat x y)
          | Lte_dur_dur, [LDuration x; LDuration y] ->
            LBool (protect o_lte_dur_dur x y)
          | Gt_int_int, [LInt x; LInt y] -> LBool (o_gt_int_int x y)
          | Gt_rat_rat, [LRat x; LRat y] -> LBool (o_gt_rat_rat x y)
          | Gt_mon_mon, [LMoney x; LMoney y] -> LBool (o_gt_mon_mon x y)
          | Gt_dat_dat, [LDate x; LDate y] -> LBool (o_gt_dat_dat x y)
          | Gt_dur_dur, [LDuration x; LDuration y] ->
            LBool (protect o_gt_dur_dur x y)
          | Gte_int_int, [LInt x; LInt y] -> LBool (o_gte_int_int x y)
          | Gte_rat_rat, [LRat x; LRat y] -> LBool (o_gte_rat_rat x y)
          | Gte_mon_mon, [LMoney x; LMoney y] -> LBool (o_gte_mon_mon x y)
          | Gte_dat_dat, [LDate x; LDate y] -> LBool (o_gte_dat_dat x y)
          | Gte_dur_dur, [LDuration x; LDuration y] ->
            LBool (protect o_gte_dur_dur x y)
          | Eq_int_int, [LInt x; LInt y] -> LBool (o_eq_int_int x y)
          | Eq_rat_rat, [LRat x; LRat y] -> LBool (o_eq_rat_rat x y)
          | Eq_mon_mon, [LMoney x; LMoney y] -> LBool (o_eq_mon_mon x y)
          | Eq_dat_dat, [LDate x; LDate y] -> LBool (o_eq_dat_dat x y)
          | Eq_dur_dur, [LDuration x; LDuration y] ->
            LBool (protect o_eq_dur_dur x y)
          | ( ( Minus_int | Minus_rat | Minus_mon | Minus_dur | ToRat_int
              | ToRat_mon | ToMoney_rat | Round_rat | Round_mon | Add_int_int
              | Add_rat_rat | Add_mon_mon | Add_dat_dur | Add_dur_dur
              | Sub_int_int | Sub_rat_rat | Sub_mon_mon | Sub_dat_dat
              | Sub_dat_dur | Sub_dur_dur | Mult_int_int | Mult_rat_rat
              | Mult_mon_rat | Mult_dur_int | Div_int_int | Div_rat_rat
              | Div_mon_mon | Div_mon_rat | Lt_int_int | Lt_rat_rat | Lt_mon_mon
              | Lt_dat_dat | Lt_dur_dur | Lte_int_int | Lte_rat_rat
              | Lte_mon_mon | Lte_dat_dat | Lte_dur_dur | Gt_int_int
              | Gt_rat_rat | Gt_mon_mon | Gt_dat_dat | Gt_dur_dur | Gte_int_int
              | Gte_rat_rat | Gte_mon_mon | Gte_dat_dat | Gte_dur_dur
              | Eq_int_int | Eq_rat_rat | Eq_mon_mon | Eq_dat_dat | Eq_dur_dur
                ),
              _ ) ->
            err ()
        in
        ELit rlit)
      ~overloaded:(fun _ -> assert false)

and evaluate_expr (ctx : decl_ctx) (e : 'm Ast.expr) : 'm Ast.expr =
  match Marked.unmark e with
  | EVar _ ->
    Errors.raise_spanned_error (Expr.pos e)
      "free variable found at evaluation (should not happen if term was \
       well-typed)"
  | EApp { f = e1; args } -> (
    let e1 = evaluate_expr ctx e1 in
    let args = List.map (evaluate_expr ctx) args in
    match Marked.unmark e1 with
    | EAbs { binder; _ } ->
      if Bindlib.mbinder_arity binder = List.length args then
        evaluate_expr ctx
          (Bindlib.msubst binder (Array.of_list (List.map Marked.unmark args)))
      else
        Errors.raise_spanned_error (Expr.pos e)
          "wrong function call, expected %d arguments, got %d"
          (Bindlib.mbinder_arity binder)
          (List.length args)
    | EOp { op; _ } ->
      Marked.same_mark_as (evaluate_operator ctx op (Expr.pos e) args) e
    | ELit LEmptyError -> Marked.same_mark_as (ELit LEmptyError) e
    | _ ->
      Errors.raise_spanned_error (Expr.pos e)
        "function has not been reduced to a lambda at evaluation (should not \
         happen if the term was well-typed")
  | EAbs _ | ELit _ | EOp _ -> e (* these are values *)
  | EStruct { fields = es; name } ->
    let new_es = StructField.Map.map (evaluate_expr ctx) es in
    if StructField.Map.exists (fun _ e -> is_empty_error e) new_es then
      Marked.same_mark_as (ELit LEmptyError) e
    else Marked.same_mark_as (EStruct { fields = new_es; name }) e
  | EStructAccess { e = e1; name = s; field } -> (
    let e1 = evaluate_expr ctx e1 in
    match Marked.unmark e1 with
    | EStruct { fields = es; name = s' } -> (
      if not (StructName.equal s s') then
        Errors.raise_multispanned_error
          [None, Expr.pos e; None, Expr.pos e1]
          "Error during struct access: not the same structs (should not happen \
           if the term was well-typed)";
      match StructField.Map.find_opt field es with
      | Some e' -> e'
      | None ->
        Errors.raise_spanned_error (Expr.pos e1)
          "Invalid field access %a in struct %a (should not happen if the term \
           was well-typed)"
          StructField.format_t field StructName.format_t s)
    | ELit LEmptyError -> Marked.same_mark_as (ELit LEmptyError) e
    | _ ->
      Errors.raise_spanned_error (Expr.pos e1)
        "The expression %a should be a struct %a but is not (should not happen \
         if the term was well-typed)"
        (Expr.format ctx ~debug:true)
        e StructName.format_t s)
  | ETuple es ->
    Marked.same_mark_as (ETuple (List.map (evaluate_expr ctx) es)) e
  | ETupleAccess { e = e1; index; size } ->
    Marked.same_mark_as
      (ETupleAccess { e = evaluate_expr ctx e1; index; size })
      e
  | EInj { e = e1; name; cons } ->
    let e1' = evaluate_expr ctx e1 in
    if is_empty_error e then Marked.same_mark_as (ELit LEmptyError) e
    else Marked.same_mark_as (EInj { e = e1'; name; cons }) e
  | EMatch { e = e1; cases = es; name } -> (
    let e1 = evaluate_expr ctx e1 in
    match Marked.unmark e1 with
    | EInj { e = e1; cons; name = name' } ->
      if not (EnumName.equal name name') then
        Errors.raise_multispanned_error
          [None, Expr.pos e; None, Expr.pos e1]
          "Error during match: two different enums found (should not happen if \
           the term was well-typed)";
      let es_n =
        match EnumConstructor.Map.find_opt cons es with
        | Some es_n -> es_n
        | None ->
          Errors.raise_spanned_error (Expr.pos e)
            "sum type index error (should not happen if the term was \
             well-typed)"
      in
      let new_e = Marked.same_mark_as (EApp { f = es_n; args = [e1] }) e in
      evaluate_expr ctx new_e
    | ELit LEmptyError -> Marked.same_mark_as (ELit LEmptyError) e
    | _ ->
      Errors.raise_spanned_error (Expr.pos e1)
        "Expected a term having a sum type as an argument to a match (should \
         not happen if the term was well-typed")
  | EDefault { excepts; just; cons } -> (
    let excepts = List.map (evaluate_expr ctx) excepts in
    let empty_count = List.length (List.filter is_empty_error excepts) in
    match List.length excepts - empty_count with
    | 0 -> (
      let just = evaluate_expr ctx just in
      match Marked.unmark just with
      | ELit LEmptyError -> Marked.same_mark_as (ELit LEmptyError) e
      | ELit (LBool true) -> evaluate_expr ctx cons
      | ELit (LBool false) -> Marked.same_mark_as (ELit LEmptyError) e
      | _ ->
        Errors.raise_spanned_error (Expr.pos e)
          "Default justification has not been reduced to a boolean at \
           evaluation (should not happen if the term was well-typed")
    | 1 -> List.find (fun sub -> not (is_empty_error sub)) excepts
    | _ ->
      Errors.raise_multispanned_error
        (List.map
           (fun except ->
             Some "This consequence has a valid justification:", Expr.pos except)
           (List.filter (fun sub -> not (is_empty_error sub)) excepts))
        "There is a conflict between multiple valid consequences for assigning \
         the same variable.")
  | EIfThenElse { cond; etrue; efalse } -> (
    match Marked.unmark (evaluate_expr ctx cond) with
    | ELit (LBool true) -> evaluate_expr ctx etrue
    | ELit (LBool false) -> evaluate_expr ctx efalse
    | ELit LEmptyError -> Marked.same_mark_as (ELit LEmptyError) e
    | _ ->
      Errors.raise_spanned_error (Expr.pos cond)
        "Expected a boolean literal for the result of this condition (should \
         not happen if the term was well-typed)")
  | EArray es ->
    let new_es = List.map (evaluate_expr ctx) es in
    if List.exists is_empty_error new_es then
      Marked.same_mark_as (ELit LEmptyError) e
    else Marked.same_mark_as (EArray new_es) e
  | EErrorOnEmpty e' ->
    let e' = evaluate_expr ctx e' in
    if Marked.unmark e' = ELit LEmptyError then
      Errors.raise_spanned_error (Expr.pos e')
        "This variable evaluated to an empty term (no rule that defined it \
         applied in this situation)"
    else e'
  | EAssert e' -> (
    match Marked.unmark (evaluate_expr ctx e') with
    | ELit (LBool true) -> Marked.same_mark_as (ELit LUnit) e'
    | ELit (LBool false) -> (
      match Marked.unmark e' with
      | EErrorOnEmpty
          ( EApp
              {
                f = EOp { op; _ }, _;
                args = [((ELit _, _) as e1); ((ELit _, _) as e2)];
              },
            _ ) ->
        Errors.raise_spanned_error (Expr.pos e') "Assertion failed: %a %a %a"
          (Expr.format ctx ~debug:false)
          e1 Print.operator op
          (Expr.format ctx ~debug:false)
          e2
      | EApp
          {
            f = EOp { op = Log _; _ }, _;
            args =
              [
                ( EApp
                    {
                      f = EOp { op; _ }, _;
                      args = [((ELit _, _) as e1); ((ELit _, _) as e2)];
                    },
                  _ );
              ];
          } ->
        Errors.raise_spanned_error (Expr.pos e') "Assertion failed: %a %a %a"
          (Expr.format ctx ~debug:false)
          e1 Print.operator op
          (Expr.format ctx ~debug:false)
          e2
      | EApp
          {
            f = EOp { op; _ }, _;
            args = [((ELit _, _) as e1); ((ELit _, _) as e2)];
          } ->
        Errors.raise_spanned_error (Expr.pos e') "Assertion failed: %a %a %a"
          (Expr.format ctx ~debug:false)
          e1 Print.operator op
          (Expr.format ctx ~debug:false)
          e2
      | _ ->
        Cli.debug_format "%a" (Expr.format ctx) e';
        Errors.raise_spanned_error (Expr.pos e') "Assertion failed")
    | ELit LEmptyError -> Marked.same_mark_as (ELit LEmptyError) e
    | _ ->
      Errors.raise_spanned_error (Expr.pos e')
        "Expected a boolean literal for the result of this assertion (should \
         not happen if the term was well-typed)")

(** {1 API} *)

let interpret_program :
      'm. decl_ctx -> 'm Ast.expr -> (Uid.MarkedString.info * 'm Ast.expr) list
    =
 fun (ctx : decl_ctx) (e : 'm Ast.expr) :
     (Uid.MarkedString.info * 'm Ast.expr) list ->
  match evaluate_expr ctx e with
  | (EAbs { tys = [((TStruct s_in, _) as _targs)]; _ }, mark_e) as e -> begin
    (* At this point, the interpreter seeks to execute the scope but does not
       have a way to retrieve input values from the command line. [taus] contain
       the types of the scope arguments. For [context] arguments, we can provide
       an empty thunked term. But for [input] arguments of another type, we
       cannot provide anything so we have to fail. *)
    let taus = StructName.Map.find s_in ctx.ctx_structs in
    let application_term =
      StructField.Map.map
        (fun ty ->
          match Marked.unmark ty with
          | TArrow (ty_in, ty_out) ->
            Expr.make_abs
              [| Var.make "_" |]
              (Bindlib.box (ELit LEmptyError), Expr.with_ty mark_e ty_out)
              [ty_in] (Expr.mark_pos mark_e)
          | _ ->
            Errors.raise_spanned_error (Marked.get_mark ty)
              "This scope needs input arguments to be executed. But the Catala \
               built-in interpreter does not have a way to retrieve input \
               values from the command line, so it cannot execute this scope. \
               Please create another scope thatprovide the input arguments to \
               this one and execute it instead. ")
        taus
    in
    let to_interpret =
      Expr.make_app (Expr.box e)
        [Expr.estruct s_in application_term mark_e]
        (Expr.pos e)
    in
    match Marked.unmark (evaluate_expr ctx (Expr.unbox to_interpret)) with
    | EStruct { fields; _ } ->
      List.map
        (fun (fld, e) -> StructField.get_info fld, e)
        (StructField.Map.bindings fields)
    | _ ->
      Errors.raise_spanned_error (Expr.pos e)
        "The interpretation of a program should always yield a struct \
         corresponding to the scope variables"
  end
  | _ ->
    Errors.raise_spanned_error (Expr.pos e)
      "The interpreter can only interpret terms starting with functions having \
       thunked arguments"