catala/compiler/dcalc/interpreter.ml
2022-02-02 10:30:39 +01:00

453 lines
22 KiB
OCaml

(* 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 Utils
module A = Ast
(** {1 Helpers} *)
let is_empty_error (e : A.expr Pos.marked) : bool =
match Pos.unmark e with ELit LEmptyError -> true | _ -> false
let log_indent = ref 0
(** {1 Evaluation} *)
let rec evaluate_operator (ctx : Ast.decl_ctx) (op : A.operator Pos.marked)
(args : A.expr Pos.marked list) : A.expr Pos.marked =
(* Try to apply [div] and if a [Division_by_zero] exceptions is catched, use [op] to raise
multispanned errors. *)
let apply_div_or_raise_err (div : unit -> A.expr) (op : A.operator Pos.marked) : A.expr =
try div ()
with Division_by_zero ->
Errors.raise_multispanned_error "division by zero at runtime"
[
(Some "The division operator:", Pos.get_position op);
(Some "The null denominator:", Pos.get_position (List.nth args 1));
]
in
let get_binop_args_pos (args : (A.expr * Pos.t) list) : (string option * Pos.t) list =
[ (None, Pos.get_position (List.nth args 0)); (None, Pos.get_position (List.nth args 1)) ]
in
(* Try to apply [cmp] and if a [UncomparableDurations] exceptions is catched, use [args] to raise
multispanned errors. *)
let apply_cmp_or_raise_err (cmp : unit -> A.expr) (args : (A.expr * Pos.t) list) : A.expr =
try cmp ()
with Runtime.UncomparableDurations ->
Errors.raise_multispanned_error
"Cannot compare together durations that cannot be converted to a precise number of days"
(get_binop_args_pos args)
in
Pos.same_pos_as
(match (Pos.unmark op, List.map Pos.unmark args) with
| A.Ternop A.Fold, [ _f; _init; EArray es ] ->
Pos.unmark
(List.fold_left
(fun acc e' ->
evaluate_expr ctx (Pos.same_pos_as (A.EApp (List.nth args 0, [ acc; e' ])) e'))
(List.nth args 1) es)
| A.Binop A.And, [ ELit (LBool b1); ELit (LBool b2) ] -> A.ELit (LBool (b1 && b2))
| A.Binop A.Or, [ ELit (LBool b1); ELit (LBool b2) ] -> A.ELit (LBool (b1 || b2))
| A.Binop A.Xor, [ ELit (LBool b1); ELit (LBool b2) ] -> A.ELit (LBool (b1 <> b2))
| A.Binop (A.Add KInt), [ ELit (LInt i1); ELit (LInt i2) ] -> A.ELit (LInt Runtime.(i1 +! i2))
| A.Binop (A.Sub KInt), [ ELit (LInt i1); ELit (LInt i2) ] -> A.ELit (LInt Runtime.(i1 -! i2))
| A.Binop (A.Mult KInt), [ ELit (LInt i1); ELit (LInt i2) ] -> A.ELit (LInt Runtime.(i1 *! i2))
| A.Binop (A.Div KInt), [ ELit (LInt i1); ELit (LInt i2) ] ->
apply_div_or_raise_err (fun _ -> A.ELit (LInt Runtime.(i1 /! i2))) op
| A.Binop (A.Add KRat), [ ELit (LRat i1); ELit (LRat i2) ] -> A.ELit (LRat Runtime.(i1 +& i2))
| A.Binop (A.Sub KRat), [ ELit (LRat i1); ELit (LRat i2) ] -> A.ELit (LRat Runtime.(i1 -& i2))
| A.Binop (A.Mult KRat), [ ELit (LRat i1); ELit (LRat i2) ] -> A.ELit (LRat Runtime.(i1 *& i2))
| A.Binop (A.Div KRat), [ ELit (LRat i1); ELit (LRat i2) ] ->
apply_div_or_raise_err (fun _ -> A.ELit (LRat Runtime.(i1 /& i2))) op
| A.Binop (A.Add KMoney), [ ELit (LMoney m1); ELit (LMoney m2) ] ->
A.ELit (LMoney Runtime.(m1 +$ m2))
| A.Binop (A.Sub KMoney), [ ELit (LMoney m1); ELit (LMoney m2) ] ->
A.ELit (LMoney Runtime.(m1 -$ m2))
| A.Binop (A.Mult KMoney), [ ELit (LMoney m1); ELit (LRat m2) ] ->
A.ELit (LMoney Runtime.(m1 *$ m2))
| A.Binop (A.Div KMoney), [ ELit (LMoney m1); ELit (LMoney m2) ] ->
apply_div_or_raise_err (fun _ -> A.ELit (LRat Runtime.(m1 /$ m2))) op
| A.Binop (A.Add KDuration), [ ELit (LDuration d1); ELit (LDuration d2) ] ->
A.ELit (LDuration Runtime.(d1 +^ d2))
| A.Binop (A.Sub KDuration), [ ELit (LDuration d1); ELit (LDuration d2) ] ->
A.ELit (LDuration Runtime.(d1 -^ d2))
| A.Binop (A.Sub KDate), [ ELit (LDate d1); ELit (LDate d2) ] ->
A.ELit (LDuration Runtime.(d1 -@ d2))
| A.Binop (A.Add KDate), [ ELit (LDate d1); ELit (LDuration d2) ] ->
A.ELit (LDate Runtime.(d1 +@ d2))
| A.Binop (A.Div KDuration), [ ELit (LDuration d1); ELit (LDuration d2) ] ->
apply_div_or_raise_err
(fun _ ->
try A.ELit (LRat Runtime.(d1 /^ d2))
with Runtime.IndivisableDurations ->
Errors.raise_multispanned_error
"Cannot divide durations that cannot be converted to a precise number of days"
(get_binop_args_pos args))
op
| A.Binop (A.Lt KInt), [ ELit (LInt i1); ELit (LInt i2) ] -> A.ELit (LBool Runtime.(i1 <! i2))
| A.Binop (A.Lte KInt), [ ELit (LInt i1); ELit (LInt i2) ] -> A.ELit (LBool Runtime.(i1 <=! i2))
| A.Binop (A.Gt KInt), [ ELit (LInt i1); ELit (LInt i2) ] -> A.ELit (LBool Runtime.(i1 >! i2))
| A.Binop (A.Gte KInt), [ ELit (LInt i1); ELit (LInt i2) ] -> A.ELit (LBool Runtime.(i1 >=! i2))
| A.Binop (A.Lt KRat), [ ELit (LRat i1); ELit (LRat i2) ] -> A.ELit (LBool Runtime.(i1 <& i2))
| A.Binop (A.Lte KRat), [ ELit (LRat i1); ELit (LRat i2) ] -> A.ELit (LBool Runtime.(i1 <=& i2))
| A.Binop (A.Gt KRat), [ ELit (LRat i1); ELit (LRat i2) ] -> A.ELit (LBool Runtime.(i1 >& i2))
| A.Binop (A.Gte KRat), [ ELit (LRat i1); ELit (LRat i2) ] -> A.ELit (LBool Runtime.(i1 >=& i2))
| A.Binop (A.Lt KMoney), [ ELit (LMoney m1); ELit (LMoney m2) ] ->
A.ELit (LBool Runtime.(m1 <$ m2))
| A.Binop (A.Lte KMoney), [ ELit (LMoney m1); ELit (LMoney m2) ] ->
A.ELit (LBool Runtime.(m1 <=$ m2))
| A.Binop (A.Gt KMoney), [ ELit (LMoney m1); ELit (LMoney m2) ] ->
A.ELit (LBool Runtime.(m1 >$ m2))
| A.Binop (A.Gte KMoney), [ ELit (LMoney m1); ELit (LMoney m2) ] ->
A.ELit (LBool Runtime.(m1 >=$ m2))
| A.Binop (A.Lt KDuration), [ ELit (LDuration d1); ELit (LDuration d2) ] ->
apply_cmp_or_raise_err (fun _ -> A.ELit (LBool Runtime.(d1 <^ d2))) args
| A.Binop (A.Lte KDuration), [ ELit (LDuration d1); ELit (LDuration d2) ] ->
apply_cmp_or_raise_err (fun _ -> A.ELit (LBool Runtime.(d1 <=^ d2))) args
| A.Binop (A.Gt KDuration), [ ELit (LDuration d1); ELit (LDuration d2) ] ->
apply_cmp_or_raise_err (fun _ -> A.ELit (LBool Runtime.(d1 >^ d2))) args
| A.Binop (A.Gte KDuration), [ ELit (LDuration d1); ELit (LDuration d2) ] ->
apply_cmp_or_raise_err (fun _ -> A.ELit (LBool Runtime.(d1 >=^ d2))) args
| A.Binop (A.Lt KDate), [ ELit (LDate d1); ELit (LDate d2) ] ->
A.ELit (LBool Runtime.(d1 <@ d2))
| A.Binop (A.Lte KDate), [ ELit (LDate d1); ELit (LDate d2) ] ->
A.ELit (LBool Runtime.(d1 <=@ d2))
| A.Binop (A.Gt KDate), [ ELit (LDate d1); ELit (LDate d2) ] ->
A.ELit (LBool Runtime.(d1 >@ d2))
| A.Binop (A.Gte KDate), [ ELit (LDate d1); ELit (LDate d2) ] ->
A.ELit (LBool Runtime.(d1 >=@ d2))
| A.Binop A.Eq, [ ELit LUnit; ELit LUnit ] -> A.ELit (LBool true)
| A.Binop A.Eq, [ ELit (LDuration d1); ELit (LDuration d2) ] ->
A.ELit (LBool Runtime.(d1 =^ d2))
| A.Binop A.Eq, [ ELit (LDate d1); ELit (LDate d2) ] -> A.ELit (LBool Runtime.(d1 =@ d2))
| A.Binop A.Eq, [ ELit (LMoney m1); ELit (LMoney m2) ] -> A.ELit (LBool Runtime.(m1 =$ m2))
| A.Binop A.Eq, [ ELit (LRat i1); ELit (LRat i2) ] -> A.ELit (LBool Runtime.(i1 =& i2))
| A.Binop A.Eq, [ ELit (LInt i1); ELit (LInt i2) ] -> A.ELit (LBool Runtime.(i1 =! i2))
| A.Binop A.Eq, [ ELit (LBool b1); ELit (LBool b2) ] -> A.ELit (LBool (b1 = b2))
| A.Binop A.Eq, [ EArray es1; EArray es2 ] ->
A.ELit
(LBool
(try
List.for_all2
(fun e1 e2 ->
match Pos.unmark (evaluate_operator ctx op [ e1; e2 ]) with
| A.ELit (LBool b) -> b
| _ -> assert false
(* should not happen *))
es1 es2
with Invalid_argument _ -> false))
| A.Binop A.Eq, [ ETuple (es1, s1); ETuple (es2, s2) ] ->
A.ELit
(LBool
(try
s1 = s2
&& List.for_all2
(fun e1 e2 ->
match Pos.unmark (evaluate_operator ctx op [ e1; e2 ]) with
| A.ELit (LBool b) -> b
| _ -> assert false
(* should not happen *))
es1 es2
with Invalid_argument _ -> false))
| A.Binop A.Eq, [ EInj (e1, i1, en1, _ts1); EInj (e2, i2, en2, _ts2) ] ->
A.ELit
(LBool
(try
en1 = en2 && i1 = i2
&&
match Pos.unmark (evaluate_operator ctx op [ e1; e2 ]) with
| A.ELit (LBool b) -> b
| _ -> assert false
(* should not happen *)
with Invalid_argument _ -> false))
| A.Binop A.Eq, [ _; _ ] -> A.ELit (LBool false) (* comparing anything else return false *)
| A.Binop A.Neq, [ _; _ ] -> (
match Pos.unmark (evaluate_operator ctx (Pos.same_pos_as (A.Binop A.Eq) op) args) with
| A.ELit (A.LBool b) -> A.ELit (A.LBool (not b))
| _ -> assert false (*should not happen *))
| A.Binop A.Concat, [ A.EArray es1; A.EArray es2 ] -> A.EArray (es1 @ es2)
| A.Binop A.Map, [ _; A.EArray es ] ->
A.EArray
(List.map
(fun e' -> evaluate_expr ctx (Pos.same_pos_as (A.EApp (List.nth args 0, [ e' ])) e'))
es)
| A.Binop A.Filter, [ _; A.EArray es ] ->
A.EArray
(List.filter
(fun e' ->
match evaluate_expr ctx (Pos.same_pos_as (A.EApp (List.nth args 0, [ e' ])) e') with
| A.ELit (A.LBool b), _ -> b
| _ ->
Errors.raise_spanned_error
"This predicate evaluated to something else than a boolean (should not happen \
if the term was well-typed)"
(Pos.get_position (List.nth args 0)))
es)
| A.Binop _, ([ ELit LEmptyError; _ ] | [ _; ELit LEmptyError ]) -> A.ELit LEmptyError
| A.Unop (A.Minus KInt), [ ELit (LInt i) ] -> A.ELit (LInt Runtime.(integer_of_int 0 -! i))
| A.Unop (A.Minus KRat), [ ELit (LRat i) ] -> A.ELit (LRat Runtime.(decimal_of_string "0" -& i))
| A.Unop (A.Minus KMoney), [ ELit (LMoney i) ] ->
A.ELit (LMoney Runtime.(money_of_units_int 0 -$ i))
| A.Unop (A.Minus KDuration), [ ELit (LDuration i) ] -> A.ELit (LDuration Runtime.(~-^i))
| A.Unop A.Not, [ ELit (LBool b) ] -> A.ELit (LBool (not b))
| A.Unop A.Length, [ EArray es ] -> A.ELit (LInt (Runtime.integer_of_int (List.length es)))
| A.Unop A.GetDay, [ ELit (LDate d) ] -> A.ELit (LInt Runtime.(day_of_month_of_date d))
| A.Unop A.GetMonth, [ ELit (LDate d) ] -> A.ELit (LInt Runtime.(month_number_of_date d))
| A.Unop A.GetYear, [ ELit (LDate d) ] -> A.ELit (LInt Runtime.(year_of_date d))
| A.Unop A.IntToRat, [ ELit (LInt i) ] -> A.ELit (LRat Runtime.(decimal_of_integer i))
| A.Unop (A.Log (entry, infos)), [ e' ] ->
if !Cli.trace_flag then (
match entry with
| VarDef _ ->
Cli.log_print
(Format.asprintf "%*s%a %a: %s" (!log_indent * 2) "" Print.format_log_entry entry
Print.format_uid_list infos
(match e' with
(* | Ast.EAbs _ -> Cli.print_with_style [ ANSITerminal.green ] "<function>" *)
| _ ->
let expr_str =
Format.asprintf "%a" (Print.format_expr ctx ~debug:false) (e', Pos.no_pos)
in
let expr_str =
Re.Pcre.substitute ~rex:(Re.Pcre.regexp "\n\\s*")
~subst:(fun _ -> " ")
expr_str
in
Cli.print_with_style [ ANSITerminal.green ] "%s" expr_str))
| PosRecordIfTrueBool -> (
let pos = Pos.get_position op in
match (pos <> Pos.no_pos, e') with
| true, ELit (LBool true) ->
Cli.log_print
(Format.asprintf "%*s%a%s:\n%s" (!log_indent * 2) "" Print.format_log_entry
entry
(Cli.print_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_print
(Format.asprintf "%*s%a %a" (!log_indent * 2) "" Print.format_log_entry entry
Print.format_uid_list infos);
log_indent := !log_indent + 1
| EndCall ->
log_indent := !log_indent - 1;
Cli.log_print
(Format.asprintf "%*s%a %a" (!log_indent * 2) "" Print.format_log_entry entry
Print.format_uid_list infos))
else ();
e'
| A.Unop _, [ ELit LEmptyError ] -> A.ELit LEmptyError
| _ ->
Errors.raise_multispanned_error
"Operator applied to the wrong arguments\n(should nothappen if the term was well-typed)"
([ (Some "Operator:", Pos.get_position op) ]
@ List.mapi
(fun i arg ->
( Some
(Format.asprintf "Argument n°%d, value %a" (i + 1)
(Print.format_expr ctx ~debug:true)
arg),
Pos.get_position arg ))
args))
op
and evaluate_expr (ctx : Ast.decl_ctx) (e : A.expr Pos.marked) : A.expr Pos.marked =
match Pos.unmark e with
| EVar _ ->
Errors.raise_spanned_error
"free variable found at evaluation (should not happen if term was well-typed"
(Pos.get_position e)
| EApp (e1, args) -> (
let e1 = evaluate_expr ctx e1 in
let args = List.map (evaluate_expr ctx) args in
match Pos.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 Pos.unmark args)))
else
Errors.raise_spanned_error
(Format.asprintf "wrong function call, expected %d arguments, got %d"
(Bindlib.mbinder_arity binder) (List.length args))
(Pos.get_position e)
| EOp op ->
Pos.same_pos_as (Pos.unmark (evaluate_operator ctx (Pos.same_pos_as op e1) args)) e
| ELit LEmptyError -> Pos.same_pos_as (A.ELit LEmptyError) e
| _ ->
Errors.raise_spanned_error
"function has not been reduced to a lambda at evaluation (should not happen if the \
term was well-typed"
(Pos.get_position e))
| EAbs _ | ELit _ | EOp _ -> e (* these are values *)
| ETuple (es, s) ->
let new_es = List.map (evaluate_expr ctx) es in
if List.exists is_empty_error new_es then Pos.same_pos_as (A.ELit LEmptyError) e
else Pos.same_pos_as (A.ETuple (new_es, s)) e
| ETupleAccess (e1, n, s, _) -> (
let e1 = evaluate_expr ctx e1 in
match Pos.unmark e1 with
| ETuple (es, s') -> (
(match (s, s') with
| None, None -> ()
| Some s, Some s' when s = s' -> ()
| _ ->
Errors.raise_multispanned_error
"Error during tuple access: not the same structs (should not happen if the term \
was well-typed)"
[ (None, Pos.get_position e); (None, Pos.get_position e1) ]);
match List.nth_opt es n with
| Some e' -> e'
| None ->
Errors.raise_spanned_error
(Format.asprintf
"The tuple has %d components but the %i-th element was requested (should not \
happen if the term was well-type)"
(List.length es) n)
(Pos.get_position e1))
| ELit LEmptyError -> Pos.same_pos_as (A.ELit LEmptyError) e
| _ ->
Errors.raise_spanned_error
(Format.asprintf
"The expression %a should be a tuple with %d components but is not (should not \
happen if the term was well-typed)"
(Print.format_expr ctx ~debug:true)
e n)
(Pos.get_position e1))
| EInj (e1, n, en, ts) ->
let e1' = evaluate_expr ctx e1 in
if is_empty_error e1' then Pos.same_pos_as (A.ELit LEmptyError) e
else Pos.same_pos_as (A.EInj (e1', n, en, ts)) e
| EMatch (e1, es, e_name) -> (
let e1 = evaluate_expr ctx e1 in
match Pos.unmark e1 with
| A.EInj (e1, n, e_name', _) ->
if e_name <> e_name' then
Errors.raise_multispanned_error
"Error during match: two different enums found (should not happend if the term was \
well-typed)"
[ (None, Pos.get_position e); (None, Pos.get_position e1) ];
let es_n =
match List.nth_opt es n with
| Some es_n -> es_n
| None ->
Errors.raise_spanned_error
"sum type index error (should not happend if the term was well-typed)"
(Pos.get_position e)
in
let new_e = Pos.same_pos_as (A.EApp (es_n, [ e1 ])) e in
evaluate_expr ctx new_e
| A.ELit A.LEmptyError -> Pos.same_pos_as (A.ELit A.LEmptyError) e
| _ ->
Errors.raise_spanned_error
"Expected a term having a sum type as an argument to a match (should not happend if \
the term was well-typed"
(Pos.get_position e1))
| EDefault (exceptions, just, cons) -> (
let exceptions = List.map (evaluate_expr ctx) exceptions in
let empty_count = List.length (List.filter is_empty_error exceptions) in
match List.length exceptions - empty_count with
| 0 -> (
let just = evaluate_expr ctx just in
match Pos.unmark just with
| ELit LEmptyError -> Pos.same_pos_as (A.ELit LEmptyError) e
| ELit (LBool true) -> evaluate_expr ctx cons
| ELit (LBool false) -> Pos.same_pos_as (A.ELit LEmptyError) e
| _ ->
Errors.raise_spanned_error
"Default justification has not been reduced to a boolean at evaluation (should not \
happen if the term was well-typed"
(Pos.get_position e))
| 1 -> List.find (fun sub -> not (is_empty_error sub)) exceptions
| _ ->
Errors.raise_multispanned_error
"There is a conflict between multiple validd consequences for assigning the same \
variable."
(List.map
(fun except ->
(Some "This consequence has a valid justification:", Pos.get_position except))
(List.filter (fun sub -> not (is_empty_error sub)) exceptions)))
| EIfThenElse (cond, et, ef) -> (
match Pos.unmark (evaluate_expr ctx cond) with
| ELit (LBool true) -> evaluate_expr ctx et
| ELit (LBool false) -> evaluate_expr ctx ef
| ELit LEmptyError -> Pos.same_pos_as (A.ELit LEmptyError) e
| _ ->
Errors.raise_spanned_error
"Expected a boolean literal for the result of this condition (should not happen if the \
term was well-typed)"
(Pos.get_position cond))
| EArray es ->
let new_es = List.map (evaluate_expr ctx) es in
if List.exists is_empty_error new_es then Pos.same_pos_as (A.ELit LEmptyError) e
else Pos.same_pos_as (A.EArray new_es) e
| ErrorOnEmpty e' ->
let e' = evaluate_expr ctx e' in
if Pos.unmark e' = A.ELit LEmptyError then
Errors.raise_spanned_error
"This variable evaluated to an empty term (no rule that defined it applied in this \
situation)"
(Pos.get_position e)
else e'
| EAssert e' -> (
match Pos.unmark (evaluate_expr ctx e') with
| ELit (LBool true) -> Pos.same_pos_as (Ast.ELit LUnit) e'
| ELit (LBool false) -> (
match Pos.unmark e' with
| EApp ((Ast.EOp (Binop op), pos_op), [ ((ELit _, _) as e1); ((ELit _, _) as e2) ]) ->
Errors.raise_spanned_error
(Format.asprintf "Assertion failed: %a %a %a"
(Print.format_expr ctx ~debug:false)
e1 Print.format_binop (op, pos_op)
(Print.format_expr ctx ~debug:false)
e2)
(Pos.get_position e')
| _ ->
Errors.raise_spanned_error (Format.asprintf "Assertion failed") (Pos.get_position e'))
| ELit LEmptyError -> Pos.same_pos_as (A.ELit LEmptyError) e
| _ ->
Errors.raise_spanned_error
"Expected a boolean literal for the result of this assertion (should not happen if the \
term was well-typed)"
(Pos.get_position e'))
(** {1 API} *)
let interpret_program (ctx : Ast.decl_ctx) (e : Ast.expr Pos.marked) :
(Uid.MarkedString.info * Ast.expr Pos.marked) list =
match Pos.unmark (evaluate_expr ctx e) with
| Ast.EAbs (_, [ (Ast.TTuple (taus, Some s_in), _) ]) -> (
let application_term = List.map (fun _ -> Ast.empty_thunked_term) taus in
let to_interpret =
(Ast.EApp (e, [ (Ast.ETuple (application_term, Some s_in), Pos.no_pos) ]), Pos.no_pos)
in
match Pos.unmark (evaluate_expr ctx to_interpret) with
| Ast.ETuple (args, Some s_out) ->
let s_out_fields =
List.map
(fun (f, _) -> Ast.StructFieldName.get_info f)
(Ast.StructMap.find s_out ctx.ctx_structs)
in
List.map2 (fun arg var -> (var, arg)) args s_out_fields
| _ ->
Errors.raise_spanned_error
"The interpretation of a program should always yield a struct corresponding to the \
scope variables"
(Pos.get_position e))
| _ ->
Errors.raise_spanned_error
"The interpreter can only interpret terms starting with functions having thunked arguments"
(Pos.get_position e)