Why isn't this ambiguous?

Why isn't this ambiguous?

[Anonymous]

Here's some code:

with Ada.Text_Io;

use Ada;
procedure F_Test is
   subtype I_Num is Integer range 1 ..      5;
   subtype O_Num is Integer range 0 .. 99_999;

   function Image (I : I_Num) return Character is
      Img : constant String := Integer'Image (I);
   begin
      Text_Io.Put_Line ("This is Image 1");

      return Img (Img'Last);
   end Image;

   function Make (I : I_Num; O : O_Num) return String is
      function Image (O : O_Num) return String is
         Img : String := Integer'Image (O);
      begin
         Text_Io.Put_Line ("This is Image 2");

         Img (Img'First) := '0';

   end Image;

   function Make (I : I_Num; O : O_Num) return String is
      function Image (O : O_Num) return String is
         Img : String := Integer'Image (O);
      begin
         Text_Io.Put_Line ("This is Image 2");

         Img (Img'First) := '0';

         if Img'Length > 5 then
            return Img (Img'First + 1 .. Img'Last);
         end if;

         return (1 .. 5 - Img'Length => '0') & Img;
      end Image;
   begin
      return Image (I) & '_' & Image (O);
   end Make;
begin
   Text_Io.Put_Line (Make (2,     1) );
   Text_Io.Put_Line (Make (3, 1_000) );
end F_Test;


With GNAT 3.07/Solaris/Sparc and 3.09/Linux/Pentium, this compiles and
produces this output:

This is Image 1
This is Image 1
2_1
This is Image 1

raised CONSTRAINT_ERROR


I expected the calls to Image to be ambiguous, but GNAT has chosen the
one that returns Character. Anyone able to provide insight?

Jeff Carter  PGP:1024/440FBE21
My real e-mail address: ( carter @ innocon . com )
"I blow my nose on you."
Monty Python & the Holy Grail

Posted with Spam Hater - see
http://www.compulink.co.uk/~net-services/spam/

Re: Why isn't this ambiguous?

[Robert Dewar]

Here is my best guess at what Jeff Carter meant:

with Ada.Text_Io;

use Ada;
procedure F_Test is
   subtype I_Num is Integer range 1 ..      5;
   subtype O_Num is Integer range 0 .. 99_999;

   function Image (I : I_Num) return Character is
      Img : constant String := Integer'Image (I);
   begin
      Text_Io.Put_Line ("This is Image 1");

      return Img (Img'Last);
   end Image;

   function Make (I : I_Num; O : O_Num) return String is
      function Image (O : O_Num) return String is
         Img : String := Integer'Image (O);
      begin
         Text_Io.Put_Line ("This is Image 2");

         Img (Img'First) := '0';

         if Img'Length > 5 then
            return Img (Img'First + 1 .. Img'Last);
         end if;

         return (1 .. 5 - Img'Length => '0') & Img;
      end Image;
   begin
      return Image (I) & '_' & Image (O);
   end Make;
begin
   Text_Io.Put_Line (Make (2,     1) );
   Text_Io.Put_Line (Make (3, 1_000) );
end F_Test;

If this guess is right, the above program is definitely illegal due to the
ambiguity in the calls to the Image function, since I_Num and O_Num are
the same type.

Re: Why isn't this ambiguous?

[Robert Dewar]

iJeff asked a question about a program with Image and Make functions
and wondered why it was not ambiguous. Something went wrong in the
posting of this message, and the resulting procedure is obviously
syntactically illegal, and furthermore, I cannot guess what it was
supposed to be. Jeff, pleasse repost!

Re: Why isn't this ambiguous?

[Anonymous]

<199708011539.RAA04612@basement.replay.com>

On 2 Aug 1997 17:15:50 -0400, dewar@merv.cs.nyu.edu (Robert Dewar)
wrote:

> iJeff asked a question about a program with Image and Make functions
> and wondered why it was not ambiguous. Something went wrong in the
> posting of this message, and the resulting procedure is obviously
> syntactically illegal, and furthermore, I cannot guess what it was
> supposed to be. Jeff, pleasse repost!
> 

Yep, sorry, I got some of the code in there twice. I'll try to do better
this time:

Here's some code:

with Ada.Text_Io;

use Ada;
procedure F_Test is
   subtype I_Num is Integer range 1 ..      5;
   subtype O_Num is Integer range 0 .. 99_999;

   function Image (I : I_Num) return Character is
      Img : constant String := Integer'Image (I);
   begin
      Text_Io.Put_Line ("This is Image 1");

      return Img (Img'Last);
   end Image;

   function Make (I : I_Num; O : O_Num) return String is
      function Image (O : O_Num) return String is
         Img : String := Integer'Image (O);
      begin
         Text_Io.Put_Line ("This is Image 2");

         Img (Img'First) := '0';

         if Img'Length > 5 then
            return Img (Img'First + 1 .. Img'Last);
         end if;

         return (1 .. 5 - Img'Length => '0') & Img;
      end Image;
   begin
      return Image (I) & '_' & Image (O);
   end Make;
begin
   Text_Io.Put_Line (Make (2,     1) );
   Text_Io.Put_Line (Make (3, 1_000) );
end F_Test;


With GNAT 3.07/Solaris/Sparc and 3.09/Linux/Pentium, this compiles and
produces this output:

This is Image 1
This is Image 1
2_1
This is Image 1

raised CONSTRAINT_ERROR


I expected the calls to Image to be ambiguous, but GNAT has chosen the
one that returns Character. Anyone able to provide insight?

Jeff Carter  PGP:1024/440FBE21
My real e-mail address: ( carter @ innocon . com )
"I unclog my nose towards you."
Monty Python & the Holy Grail

Posted with Spam Hater - see
http://www.compulink.co.uk/~net-services/spam/

Re: Why isn't this ambiguous?

[Robert A Duff]

In article <199708041340.PAA25417@basement.replay.com>,
Anonymous <nobody@REPLAY.COM> wrote:
>I expected the calls to Image to be ambiguous, but GNAT has chosen the
>one that returns Character. Anyone able to provide insight?

I agree that it's ambiguous.

- Bob

Re: Why isn't this ambiguous?

[Robert Dewar]

Bob said

<<I agree that it's ambiguous.>>

My newsreader must have lost (or destroyed :-) a post. I still don't have
an example from the original poster that is anywhere near syntactically
correct.