Index: src/natools-s_expressions.adb
==================================================================
--- src/natools-s_expressions.adb
+++ src/natools-s_expressions.adb
@@ -48,6 +48,35 @@
       pragma Unreferenced (Discarded);
    begin
       Next (Object, Discarded);
    end Next;
 
+
+   procedure Close_Current_List (Object : in out Descriptor'Class) is
+      Level : Natural := 0;
+      Event : Events.Event := Object.Current_Event;
+   begin
+      if Object.Current_Event in Events.Error | Events.End_Of_Input then
+         return;
+      end if;
+
+      loop
+         Object.Next (Event);
+
+         case Event is
+            when Events.Error | Events.End_Of_Input =>
+               exit;
+
+            when Events.Open_List =>
+               Level := Level + 1;
+
+            when Events.Close_List =>
+               exit when Level = 0;
+               Level := Level - 1;
+
+            when Events.Add_Atom =>
+               null;
+         end case;
+      end loop;
+   end Close_Current_List;
+
 end Natools.S_Expressions;

Index: src/natools-s_expressions.ads
==================================================================
--- src/natools-s_expressions.ads
+++ src/natools-s_expressions.ads
@@ -113,14 +113,21 @@
       Event : out Events.Event) is abstract;
       --  Update Object to reflect the next event in the S-expression
 
    procedure Next (Object : in out Descriptor'Class);
       --  Call Next discarding current event
+
+   procedure Close_Current_List (Object : in out Descriptor'Class);
+      --  Repeatedly call Next until reaching end-of-input or the Close_List
+      --  event matching the current list.
+      --  Note: if current event is Open_List, then this is the designated list
+      --  while for other events, including Close_List, the designated list
+      --  contains the current object or the just-closed list.
 
 private
 
    use type Ada.Streams.Stream_Element;
    use type Ada.Streams.Stream_Element_Offset;
    use type Ada.Streams.Stream_Element_Array;
    use type Events.Event;
 
 end Natools.S_Expressions;