Index: src/natools-s_expressions-printers.adb
==================================================================
--- src/natools-s_expressions-printers.adb
+++ src/natools-s_expressions-printers.adb
@@ -41,6 +41,36 @@
    overriding procedure Close_List (Output : in out Canonical) is
    begin
       Output.Stream.Write ((0 => Encodings.List_End));
    end Close_List;
 
+
+   procedure Transfer
+     (Source : in out Descriptor'Class;
+      Target : in out Printer'Class)
+   is
+      procedure Print_Atom (Data : in Atom);
+
+      procedure Print_Atom (Data : in Atom) is
+      begin
+         Target.Append_Atom (Data);
+      end Print_Atom;
+
+      Event : Events.Event := Source.Current_Event;
+   begin
+      loop
+         case Event is
+            when Events.Error | Events.End_Of_Input =>
+               exit;
+            when Events.Open_List =>
+               Target.Open_List;
+            when Events.Close_List =>
+               Target.Close_List;
+            when Events.Add_Atom =>
+               Source.Query_Atom (Print_Atom'Access);
+         end case;
+
+         Source.Next (Event);
+      end loop;
+   end Transfer;
+
 end Natools.S_Expressions.Printers;

Index: src/natools-s_expressions-printers.ads
==================================================================
--- src/natools-s_expressions-printers.ads
+++ src/natools-s_expressions-printers.ads
@@ -37,14 +37,18 @@
 
    procedure Open_List (Output : in out Printer) is abstract;
    procedure Append_Atom (Output : in out Printer; Data : in Atom) is abstract;
    procedure Close_List (Output : in out Printer) is abstract;
 
+   procedure Transfer
+     (Source : in out Descriptor'Class;
+      Target : in out Printer'Class);
+
    type Canonical (Stream : access Ada.Streams.Root_Stream_Type'Class) is
      new Printer with null record;
 
    overriding procedure Open_List (Output : in out Canonical);
    overriding procedure Append_Atom (Output : in out Canonical;
                                      Data : in Atom);
    overriding procedure Close_List (Output : in out Canonical);
 
 end Natools.S_Expressions.Printers;