diff --git a/build_system/clerk_driver.ml b/build_system/clerk_driver.ml
index 55a0ed32..f377c377 100644
--- a/build_system/clerk_driver.ml
+++ b/build_system/clerk_driver.ml
@@ -935,7 +935,16 @@ let ninja_cmdline ninja_flags nin_file targets =
 let run_ninja ~clean_up_env cmdline =
   let cmd = List.hd cmdline in
   let env = if clean_up_env then cleaned_up_env () else Unix.environment () in
-  Unix.execvpe cmd (Array.of_list cmdline) env
+  let npid =
+    Unix.create_process_env cmd (Array.of_list cmdline) env Unix.stdin
+      Unix.stdout Unix.stderr
+  in
+  let return_code =
+    match Unix.waitpid [] npid with
+    | _, Unix.WEXITED n -> n
+    | _, (Unix.WSIGNALED n | Unix.WSTOPPED n) -> 128 - n
+  in
+  raise (Catala_utils.Cli.Exit_with return_code)
 
 open Cmdliner
 
diff --git a/compiler/shared_ast/interpreter.ml b/compiler/shared_ast/interpreter.ml
index 0c1a2ccc..5e73afa3 100644
--- a/compiler/shared_ast/interpreter.ml
+++ b/compiler/shared_ast/interpreter.ml
@@ -34,30 +34,88 @@ let is_empty_error : type a. (a, 'm) gexpr -> bool =
 let indent_str = ref ""
 
 (** {1 Evaluation} *)
-let print_log lang entry infos pos e =
-  if Global.options.trace then
-    match entry with
-    | VarDef _ ->
-      Message.log "%s%a %a: @{<green>%s@}" !indent_str Print.log_entry entry
-        Print.uid_list infos
-        (Message.unformat (fun ppf ->
-             (if Global.options.debug then Print.expr ~debug:true ()
-              else Print.UserFacing.expr lang)
-               ppf e))
-    | PosRecordIfTrueBool -> (
-      match pos <> Pos.no_pos, Mark.remove e with
-      | true, ELit (LBool true) ->
-        Message.log "%s@[<v>%a@{<green>Definition applied@}:@,%a@]" !indent_str
-          Print.log_entry entry Pos.format_loc_text pos
-      | _ -> ())
-    | BeginCall ->
-      Message.log "%s%a %a" !indent_str Print.log_entry entry Print.uid_list
-        infos;
-      indent_str := !indent_str ^ "  "
-    | EndCall ->
-      indent_str := String.sub !indent_str 0 (String.length !indent_str - 2);
-      Message.log "%s%a %a" !indent_str Print.log_entry entry Print.uid_list
-        infos
+
+let rec format_runtime_value lang ppf = function
+  | Runtime.Unit -> Print.UserFacing.unit lang ppf ()
+  | Runtime.Bool b -> Print.UserFacing.bool lang ppf b
+  | Runtime.Money m -> Print.UserFacing.money lang ppf m
+  | Runtime.Integer i -> Print.UserFacing.integer lang ppf i
+  | Runtime.Decimal d -> Print.UserFacing.decimal lang ppf d
+  | Runtime.Date t -> Print.UserFacing.date lang ppf t
+  | Runtime.Duration dt -> Print.UserFacing.duration lang ppf dt
+  | Runtime.Enum (name, (constr, v)) ->
+    Format.fprintf ppf "@[<hov 2>%s.%s@ (%a)@]" name constr
+      (format_runtime_value lang)
+      v
+  | Runtime.Struct (name, fields) ->
+    Format.fprintf ppf "@[<hv 2>%s {@ %a@;<1 -2>}@]" name
+      (Format.pp_print_list ~pp_sep:Format.pp_print_space (fun ppf (fld, v) ->
+           Format.fprintf ppf "@[<hov 2>-- %s:@ %a@]" fld
+             (format_runtime_value lang)
+             v))
+      fields
+  | Runtime.Array elts ->
+    Format.fprintf ppf "@[<hv 2>[@,@[<hov>%a@]@;<0 -2>]@]"
+      (Format.pp_print_list
+         ~pp_sep:(fun ppf () -> Format.fprintf ppf ";@ ")
+         (format_runtime_value lang))
+      (Array.to_list elts)
+  | Runtime.Unembeddable -> Format.pp_print_string ppf "<object>"
+
+let print_log lang entry =
+  let pp_infos =
+    Format.(
+      pp_print_list
+        ~pp_sep:(fun ppf () -> Format.fprintf ppf ".@,")
+        pp_print_string)
+  in
+  match entry with
+  | Runtime.BeginCall infos ->
+    Message.log "%s%a %a" !indent_str Print.log_entry BeginCall pp_infos infos;
+    indent_str := !indent_str ^ "  "
+  | Runtime.EndCall infos ->
+    indent_str := String.sub !indent_str 0 (String.length !indent_str - 2);
+    Message.log "%s%a %a" !indent_str Print.log_entry EndCall pp_infos infos
+  | Runtime.VariableDefinition (infos, io, value) ->
+    Message.log "%s%a %a: @{<green>%s@}" !indent_str Print.log_entry
+      (VarDef
+         {
+           log_typ = TAny;
+           log_io_input = io.Runtime.io_input;
+           log_io_output = io.Runtime.io_output;
+         })
+      pp_infos infos
+      (Message.unformat (fun ppf -> format_runtime_value lang ppf value))
+  | Runtime.DecisionTaken rtpos ->
+    let pos = Expr.runtime_to_pos rtpos in
+    Message.log "%s@[<v>%a@{<green>Definition applied@}:@,%a@]" !indent_str
+      Print.log_entry PosRecordIfTrueBool Pos.format_loc_text pos
+
+let rec value_to_runtime_embedded = function
+  | ELit LUnit -> Runtime.Unit
+  | ELit (LBool b) -> Runtime.Bool b
+  | ELit (LMoney m) -> Runtime.Money m
+  | ELit (LInt i) -> Runtime.Integer i
+  | ELit (LRat r) -> Runtime.Decimal r
+  | ELit (LDate d) -> Runtime.Date d
+  | ELit (LDuration dt) -> Runtime.Duration dt
+  | EInj { name; cons; e } ->
+    Runtime.Enum
+      ( EnumName.to_string name,
+        ( EnumConstructor.to_string cons,
+          value_to_runtime_embedded (Mark.remove e) ) )
+  | EStruct { name; fields } ->
+    Runtime.Struct
+      ( StructName.to_string name,
+        List.map
+          (fun (f, e) ->
+            StructField.to_string f, value_to_runtime_embedded (Mark.remove e))
+          (StructField.Map.bindings fields) )
+  | EArray el ->
+    Runtime.Array
+      (Array.of_list
+         (List.map (fun e -> value_to_runtime_embedded (Mark.remove e)) el))
+  | _ -> Runtime.Unembeddable
 
 (* Todo: this should be handled early when resolving overloads. Here we have
    proper structural equality, but the OCaml backend for example uses the
@@ -147,9 +205,22 @@ let rec evaluate_operator
   match op, args with
   | Length, [(EArray es, _)] ->
     ELit (LInt (Runtime.integer_of_int (List.length es)))
-  | Log (entry, infos), [e'] ->
-    print_log lang entry infos pos e';
-    Mark.remove e'
+  | Log (entry, infos), [(e, _)] when Global.options.trace -> (
+    let rtinfos = List.map Uid.MarkedString.to_string infos in
+    match entry with
+    | BeginCall -> Runtime.log_begin_call rtinfos e
+    | EndCall -> Runtime.log_end_call rtinfos e
+    | PosRecordIfTrueBool ->
+      (match e with
+      | ELit (LBool b) ->
+        Runtime.log_decision_taken (Expr.pos_to_runtime pos) b |> ignore
+      | _ -> ());
+      e
+    | VarDef def ->
+      Runtime.log_variable_definition rtinfos
+        { Runtime.io_input = def.log_io_input; io_output = def.log_io_output }
+        value_to_runtime_embedded e)
+  | Log _, [(e', _)] -> e'
   | (FromClosureEnv | ToClosureEnv), [e'] ->
     (* [FromClosureEnv] and [ToClosureEnv] are just there to bypass the need for
        existential types when typing code after closure conversion. There are
@@ -840,6 +911,22 @@ and partially_evaluate_expr_for_assertion_failure_message :
       Mark.get e )
   | _ -> evaluate_expr ctx lang e
 
+let evaluate_expr_trace :
+    type d e.
+    decl_ctx ->
+    Global.backend_lang ->
+    ((d, e, yes) interpr_kind, 't) gexpr ->
+    ((d, e, yes) interpr_kind, 't) gexpr =
+ fun ctx lang e ->
+  Fun.protect
+    (fun () -> evaluate_expr ctx lang e)
+    ~finally:(fun () ->
+      if Global.options.trace then
+        let trace = Runtime.retrieve_log () in
+        List.iter (print_log lang) trace
+        (* TODO: [Runtime.pp_events ~is_first_call:true Format.err_formatter
+           (Runtime.EventParser.parse_raw_events trace)] fais here, check why *))
+
 let evaluate_expr_safe :
     type d e.
     decl_ctx ->
@@ -847,7 +934,7 @@ let evaluate_expr_safe :
     ((d, e, yes) interpr_kind, 't) gexpr ->
     ((d, e, yes) interpr_kind, 't) gexpr =
  fun ctx lang e ->
-  try evaluate_expr ctx lang e
+  try evaluate_expr_trace ctx lang e
   with Runtime.Error (err, rpos) ->
     Message.error
       ~extra_pos:(List.map (fun rp -> "", Expr.runtime_to_pos rp) rpos)
diff --git a/compiler/surface/parser_driver.ml b/compiler/surface/parser_driver.ml
index 4244ae1d..b1474823 100644
--- a/compiler/surface/parser_driver.ml
+++ b/compiler/surface/parser_driver.ml
@@ -79,7 +79,7 @@ let raise_parser_error
         | None -> "Error token", error_loc
         | Some last_good_loc -> "Last good token", last_good_loc);
       ]
-    "Syntax error at %a@\n%t"
+    "@[<hov>Syntax error at %a:@ %t@]"
     (fun ppf string -> Format.fprintf ppf "@{<yellow>\"%s\"@}" string)
     token msg
 
@@ -131,10 +131,11 @@ module ParserAux (LocalisedLexer : Lexer_common.LocalisedLexer) = struct
       (match Parser_errors.message (state env) with
       | exception Not_found -> Format.fprintf ppf "@{<yellow>unexpected token@}"
       | msg ->
-        Format.fprintf ppf "@{<yellow>@<1>»@} @[<hov>%a@]" Format.pp_print_text
+        Format.fprintf ppf "@{<yellow>@<1>%s@} @[<hov>%a@]" "»"
+          Format.pp_print_text
           (String.trim (String.uncapitalize_ascii msg)));
       if acceptable_tokens <> [] then
-        Format.fprintf ppf "@,@[<hov>Those are valid at this point:@ %a@]"
+        Format.fprintf ppf "@\n@[<hov>Those are valid at this point:@ %a@]"
           (Format.pp_print_list
              ~pp_sep:(fun ppf () -> Format.fprintf ppf ",@ ")
              (fun ppf string -> Format.fprintf ppf "@{<yellow>\"%s\"@}" string))
diff --git a/tests/default/bad/typing_or_logical_error.catala_en b/tests/default/bad/typing_or_logical_error.catala_en
index 699f337d..ea830470 100644
--- a/tests/default/bad/typing_or_logical_error.catala_en
+++ b/tests/default/bad/typing_or_logical_error.catala_en
@@ -13,7 +13,7 @@ scope A:
 $ catala test-scope A
 ┌─[ERROR]─
 │
-│  Syntax error at "="
+│  Syntax error at "=":
 │  » expected 'under condition' followed by a condition, 'equals' followed by
 │    the definition body, or the rest of the variable qualified name
 │  Those are valid at this point: "of", "state", "equals", "under condition",
diff --git a/tests/scope/good/scope_call3.catala_en b/tests/scope/good/scope_call3.catala_en
index c43a290c..2cd17652 100644
--- a/tests/scope/good/scope_call3.catala_en
+++ b/tests/scope/good/scope_call3.catala_en
@@ -44,7 +44,7 @@ $ catala Interpret -t -s HousingComputation --debug
 [DEBUG] Translating to default calculus...
 [DEBUG] Typechecking again...
 [DEBUG] Starting interpretation...
-[LOG] ≔  HousingComputation.f: λ (x_67: integer) → error_empty ⟨ ⟨#{☛ } true ⊢ ⟨(let result_68 : RentComputation = (#{→ RentComputation.direct} (λ (RentComputation_in_69: RentComputation_in) → let g_70 : integer → integer = #{≔ RentComputation.g} (λ (x1_71: integer) → error_empty ⟨ ⟨#{☛ } true ⊢ ⟨x1_71 +! 1⟩⟩ | false ⊢ ∅ ⟩) in let f_72 : integer → integer = #{≔ RentComputation.f} (λ (x1_73: integer) → error_empty ⟨ ⟨#{☛ } true ⊢ ⟨#{← RentComputation.g} #{≔ RentComputation.g.output} (#{→ RentComputation.g} g_70) #{≔ RentComputation.g.input0} (x1_73 +! 1)⟩⟩ | false ⊢ ∅ ⟩) in { RentComputation f = f_72; })) #{≔ RentComputation.direct.input} {RentComputation_in} in let result1_74 : RentComputation = { RentComputation f = λ (param0_75: integer) → #{← RentComputation.f} #{≔ RentComputation.f.output} (#{→ RentComputation.f} result_68.f) #{≔ RentComputation.f.input0} param0_75; } in #{← RentComputation.direct} #{≔ RentComputation.direct.output} if #{☛ RentComputation.direct.output} true then result1_74 else result1_74).f x_67⟩⟩ | false ⊢ ∅ ⟩
+[LOG] ≔  HousingComputation.f: <object>
 [LOG] ☛ Definition applied:
       ─➤ tests/scope/good/scope_call3.catala_en:8.14-8.20:
         │
@@ -58,15 +58,16 @@ $ catala Interpret -t -s HousingComputation --debug
         7 │   definition f of x equals (output of RentComputation).f of x
           │              ‾
 [LOG]   →  RentComputation.direct
-[LOG]     ≔  RentComputation.direct.input: {RentComputation_in}
-[LOG]     ≔  RentComputation.g: λ (x_76: integer) → error_empty ⟨ ⟨#{☛ } true ⊢ ⟨x_76 +! 1⟩⟩ | false ⊢ ∅ ⟩
-[LOG]     ≔  RentComputation.f: λ (x_77: integer) → error_empty ⟨ ⟨#{☛ } true ⊢ ⟨#{← RentComputation.g} #{≔ RentComputation.g.output} (#{→ RentComputation.g} (λ (x1_78: integer) → error_empty ⟨ ⟨#{☛ } true ⊢ ⟨x1_78 +! 1⟩⟩ | false ⊢ ∅ ⟩)) #{≔ RentComputation.g.input0} (x_77 +! 1)⟩⟩ | false ⊢ ∅ ⟩
+[LOG]     ≔  RentComputation.direct.input: RentComputation_in {  }
+[LOG]     ≔  RentComputation.g: <object>
+[LOG]     ≔  RentComputation.f: <object>
 [LOG]     ☛ Definition applied:
           ─➤ tests/scope/good/scope_call3.catala_en:7.29-7.54:
             │
           7 │   definition f of x equals (output of RentComputation).f of x
             │                             ‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
-[LOG]     ≔  RentComputation.direct.output: { RentComputation f = λ (param0_79: integer) → #{← RentComputation.f} #{≔ RentComputation.f.output} (#{→ RentComputation.f} { RentComputation f = λ (x_80: integer) → error_empty ⟨ ⟨#{☛ } true ⊢ ⟨#{← RentComputation.g} #{≔ RentComputation.g.output} (#{→ RentComputation.g} (λ (x1_81: integer) → error_empty ⟨ ⟨#{☛ } true ⊢ ⟨x1_81 +! 1⟩⟩ | false ⊢ ∅ ⟩)) #{≔ RentComputation.g.input0} (x_80 +! 1)⟩⟩ | false ⊢ ∅ ⟩; }.f) #{≔ RentComputation.f.input0} param0_79; }
+[LOG]     ≔  RentComputation.direct.
+  output: RentComputation { -- f: <object> }
 [LOG]   ←  RentComputation.direct
 [LOG]   →  RentComputation.f
 [LOG]     ≔  RentComputation.f.input0: 1