Ada Recursion with strings

[Joe <joesmoe10@gmail.com>]

Hey all,
I'm trying to write a function that converts a 2**32 mod type into an
string formatted like an IP address (i.e. 192.168.2.1).

Here's what I wrote

with Ada.Text_IO;
use  Ada.Text_IO;

procedure Ip_packet is
   type Word_Type is mod 2**32;

   function IP_String (Word : Word_Type;
                       IP_String : String := "") return String
is
      Sub_String : String := Word_Type'Image(Word mod 2**8);
   begin
      if Word <= 2**8 then
         return Word_Type'Image(Word) & IP_String;
      else
         return IP_String( Word / 2**8,
                           "." & Sub_String & IP_String);
      end if;
   end IP_String;

begin  --  Ip_packet
   Put(IP_String(123456));
end Ip_packet;

There are 2 errors with this that I don't understand.  First, Ada
expects an integer for (word / 2**8).  Is this because word_type is
outside the standard integer range?  How do I get a division operator
that works on word_type?

If I patch the integer error by type casting word to an integer I get
another error.  On the second return statement, Ada complains that
there are "too many subscripts in array reference".  Is there a
limitation on the string I can pass to a recursive function call?

Thanks,
Joe