src/Pure/Isar/outer_syntax.ML

 
     val toks = Source.exhausted (Thy_Syntax.token_source lexs pos (Source.of_string text));
     val spans = Source.exhaust (Thy_Syntax.span_source toks);
     val _ = List.app Thy_Syntax.report_span spans;
     val units = Source.exhaust (Thy_Syntax.unit_source (Source.of_list spans))
-      |> maps (prepare_unit commands);
+      |> Par_List.map (prepare_unit commands) |> flat;
 
     val _ = Present.theory_source name
       (fn () => HTML.html_mode (implode o map Thy_Syntax.present_span) spans);
 
     val _ = if time then writeln ("\n**** Starting theory " ^ quote name ^ " ****") else ();