Discriminant ans tagged type ?!

Discriminant ans tagged type ?!

[Tony]

I just do not understand why the following code compiles with the Aonix 
compiler and not with the Gnat GPL 2007?

     package A_Pkg is
         type A (L : Natural) is tagged null record;
     end A_Pkg;

     package A_Pkg.B_Pkg is
         type B is new A with record
             T : String(1..L);
         end record;
     end A_Pkg.B_Pkg;

     with A_Pkg.B_Pkg;
     procedure Strange is
     begin
         null;
     end Strange;

    => RM95 3.7 (18) ??

Re: Discriminant ans tagged type ?!

[Adam Beneschan]

On Mar 18, 8:22 am, Tony <truand.t...@gmail.com> wrote:
> I just do not understand why the following code compiles with the Aonix
> compiler and not with the Gnat GPL 2007?

Because one of the compilers has a bug.

Or did you want a *helpful* answer???  :) :) :)

>
>      package A_Pkg is
>          type A (L : Natural) is tagged null record;
>      end A_Pkg;
>
>      package A_Pkg.B_Pkg is
>          type B is new A with record
>              T : String(1..L);
>          end record;
>      end A_Pkg.B_Pkg;
>
>      with A_Pkg.B_Pkg;
>      procedure Strange is
>      begin
>          null;
>      end Strange;
>
>     => RM95 3.7 (18) ??

Yes, B inherits the discriminant L, but this doesn't make L
*visible*.  In order to use L by itself, as you did in the definition
of the component T, L has to be directly visible.  The rules for this
are in 8.1 and 8.2, and aren't easy to understand.  The applicable
rules here are that: The declaration of L (when the discriminant is
first declared) is visible up to the end of the declarative region
immediately enclosing it, which is the definition of the type A.  But
this declarative region does *not* encompass the declarations of any
type extensions.  (Also, the fact that B "inherits" L is not
equivalent to there being an implicit declaration of L; unlike
inherited subprograms, inherited discriminants aren't implicitly
declared.)  Thus, L is not directly visible within the declaration of
B.

However, I tried changing the declaration of T as follows:

   T : String (1 .. B.L);

and GNAT accepted it.  (I haven't done enough testing to make sure
GNAT handles it correctly in other ways, though.)  Here, B refers to
the "current instance" of the type (8.6(17)), and 3.7(18) means that
all instances of the type will have a component L that is inherited
from A, so this should be legal unless there are some other rules that
I've missed (and that GNAT also missed).

Hope this helps,

                                 -- Adam

Re: Discriminant ans tagged type ?!

[Adam Beneschan]

On Mar 18, 8:54 am, Adam Beneschan <a...@irvine.com> wrote:

> However, I tried changing the declaration of T as follows:
>
>    T : String (1 .. B.L);
>
> and GNAT accepted it.  (I haven't done enough testing to make sure
> GNAT handles it correctly in other ways, though.)  Here, B refers to
> the "current instance" of the type (8.6(17)), and 3.7(18) means that
> all instances of the type will have a component L that is inherited
> from A, so this should be legal unless there are some other rules that
> I've missed (and that GNAT also missed).

Never mind.  After reading Bob's post, I got pointed to 3.8(10-12),
which disallows references to inherited discriminants in a type
extension.  So I guess GNAT (or at least the version I'm using, which
is probably not the latest) is wrong to accept this.  Sorry.

                                  -- Adam

Re: Discriminant ans tagged type ?!

[Tony]

On 18 mar, 20:54, Adam Beneschan <a...@irvine.com> wrote:
> On Mar 18, 8:54 am, Adam Beneschan <a...@irvine.com> wrote:
>
> > However, I tried changing the declaration of T as follows:
>
> >    T : String (1 .. B.L);
>
> > and GNAT accepted it.  (I haven't done enough testing to make sure
> > GNAT handles it correctly in other ways, though.)  Here, B refers to
> > the "current instance" of the type (8.6(17)), and 3.7(18) means that
> > all instances of the type will have a component L that is inherited
> > from A, so this should be legal unless there are some other rules that
> > I've missed (and that GNAT also missed).
>
> Never mind.  After reading Bob's post, I got pointed to 3.8(10-12),
> which disallows references to inherited discriminants in a type
> extension.  So I guess GNAT (or at least the version I'm using, which
> is probably not the latest) is wrong to accept this.  Sorry.
>
>                                   -- Adam

--
I tried Bob's answer with the Aonix compiler:
ERROR : LRM:3.8(12), A discriminant used in a constraint may only
appear alone as a direct_name.
I'm lost...;-)
Is my first code correct? I guess yes...
Tony

Re: Discriminant ans tagged type ?!

[Adam Beneschan]

On Mar 21, 1:18 am, Tony <truand.t...@gmail.com> wrote:
> On 18 mar, 20:54, Adam Beneschan <a...@irvine.com> wrote:
>
>
>
> > On Mar 18, 8:54 am, Adam Beneschan <a...@irvine.com> wrote:
>
> > > However, I tried changing the declaration of T as follows:
>
> > >    T : String (1 .. B.L);  -- NO, THIS IS WRONG, I SCREWED UP
>
> > > and GNAT accepted it.  (I haven't done enough testing to make sure
> > > GNAT handles it correctly in other ways, though.)  Here, B refers to
> > > the "current instance" of the type (8.6(17)), and 3.7(18) means that
> > > all instances of the type will have a component L that is inherited
> > > from A, so this should be legal unless there are some other rules that
> > > I've missed (and that GNAT also missed).
>
> > Never mind.  After reading Bob's post, I got pointed to 3.8(10-12),
> > which disallows references to inherited discriminants in a type
> > extension.  So I guess GNAT (or at least the version I'm using, which
> > is probably not the latest) is wrong to accept this.  Sorry.
>
> >                                   -- Adam
>
> --
> I tried Bob's answer with the Aonix compiler:
> ERROR : LRM:3.8(12), A discriminant used in a constraint may only
> appear alone as a direct_name.
> I'm lost...;-)

3.8(12) is one of the rules I overlooked (thanks, Tuck).  Perhaps you
tried  Bob's answer together with my incorrect suggestion to use
string(1..B.L), which violates that rule; when you use a discriminant
in a constraint, the discriminant can't be an "expanded name" or part
of a larger expression, and I think B.L is an expanded name here.  My
apologies for misleading you.

This should work:

    type B (L : Natural) is new A(L) with record
         T : String (1 .. L);
    end record;

Everything I said earlier about visibility wouldn't apply here,
because redeclaring the discriminant L makes it visible inside the
record declaration of B.  This would work too:

    type B (Ell : Natural) is new A(L) with record
         T : String (1 .. Ell);
    end record;

It's the new discriminant that can be used in the declaration, not the
one inherited from A.


> Is my first code correct? I guess yes...

Still no.  The compiler may accept it, but that just means the
compiler has a bug.

I hope I've got everything straight now.

                                   -- Adam

Re: Discriminant ans tagged type ?!

[Simon Wright]

Adam Beneschan <adam@irvine.com> writes:

>     type B (Ell : Natural) is new A(L) with record
                                    A(L => Ell)
>          T : String (1 .. Ell);
>     end record;

Re: Discriminant ans tagged type ?!

[Tony]

On 21 mar, 16:25, Adam Beneschan <a...@irvine.com> wrote:
> On Mar 21, 1:18 am, Tony <truand.t...@gmail.com> wrote:
>
>
>
> > On 18 mar, 20:54, Adam Beneschan <a...@irvine.com> wrote:
>
> > > On Mar 18, 8:54 am, Adam Beneschan <a...@irvine.com> wrote:
>
> > > > However, I tried changing the declaration of T as follows:
>
> > > >    T : String (1 .. B.L);  -- NO, THIS IS WRONG, I SCREWED UP
>
> > > > and GNAT accepted it.  (I haven't done enough testing to make sure
> > > > GNAT handles it correctly in other ways, though.)  Here, B refers to
> > > > the "current instance" of the type (8.6(17)), and 3.7(18) means that
> > > > all instances of the type will have a component L that is inherited
> > > > from A, so this should be legal unless there are some other rules that
> > > > I've missed (and that GNAT also missed).
>
> > > Never mind.  After reading Bob's post, I got pointed to 3.8(10-12),
> > > which disallows references to inherited discriminants in a type
> > > extension.  So I guess GNAT (or at least the version I'm using, which
> > > is probably not the latest) is wrong to accept this.  Sorry.
>
> > >                                   -- Adam
>
> > --
> > I tried Bob's answer with the Aonix compiler:
> > ERROR : LRM:3.8(12), A discriminant used in a constraint may only
> > appear alone as a direct_name.
> > I'm lost...;-)
>
> 3.8(12) is one of the rules I overlooked (thanks, Tuck).  Perhaps you
> tried  Bob's answer together with my incorrect suggestion to use
> string(1..B.L), which violates that rule; when you use a discriminant
> in a constraint, the discriminant can't be an "expanded name" or part
> of a larger expression, and I think B.L is an expanded name here.  My
> apologies for misleading you.
>
> This should work:
>
>     type B (L : Natural) is new A(L) with record
>          T : String (1 .. L);
>     end record;
>
> Everything I said earlier about visibility wouldn't apply here,
> because redeclaring the discriminant L makes it visible inside the
> record declaration of B.  This would work too:
>
>     type B (Ell : Natural) is new A(L) with record
>          T : String (1 .. Ell);
>     end record;
>
> It's the new discriminant that can be used in the declaration, not the
> one inherited from A.
>
> > Is my first code correct? I guess yes...
>
> Still no.  The compiler may accept it, but that just means the
> compiler has a bug.
>
> I hope I've got everything straight now.
>
>                                    -- Adam
--
 You are right !!  , it works :-)
 Thanks for all.
 Tony.
--

Re: Discriminant ans tagged type ?!

[Tom Grosman]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain, Size: 2871 bytes --]

"Tony" <truand.tony@gmail.com> a �crit dans le message de news: 
cc37c7dc-d89b-4f4a-82e3-24941300efb5@k13g2000hse.googlegroups.com...
> On 21 mar, 16:25, Adam Beneschan <a...@irvine.com> wrote:
>> On Mar 21, 1:18 am, Tony <truand.t...@gmail.com> wrote:
>>
>>
>>
>> > On 18 mar, 20:54, Adam Beneschan <a...@irvine.com> wrote:
>>
>> > > On Mar 18, 8:54 am, Adam Beneschan <a...@irvine.com> wrote:
>>
>> > > > However, I tried changing the declaration of T as follows:
>>
>> > > >    T : String (1 .. B.L);  -- NO, THIS IS WRONG, I SCREWED UP
>>
>> > > > and GNAT accepted it.  (I haven't done enough testing to make sure
>> > > > GNAT handles it correctly in other ways, though.)  Here, B refers 
>> > > > to
>> > > > the "current instance" of the type (8.6(17)), and 3.7(18) means 
>> > > > that
>> > > > all instances of the type will have a component L that is inherited
>> > > > from A, so this should be legal unless there are some other rules 
>> > > > that
>> > > > I've missed (and that GNAT also missed).
>>
>> > > Never mind.  After reading Bob's post, I got pointed to 3.8(10-12),
>> > > which disallows references to inherited discriminants in a type
>> > > extension.  So I guess GNAT (or at least the version I'm using, which
>> > > is probably not the latest) is wrong to accept this.  Sorry.
>>
>> > >                                   -- Adam
>>
>> > --
>> > I tried Bob's answer with the Aonix compiler:
>> > ERROR : LRM:3.8(12), A discriminant used in a constraint may only
>> > appear alone as a direct_name.
>> > I'm lost...;-)
>>
>> 3.8(12) is one of the rules I overlooked (thanks, Tuck).  Perhaps you
>> tried  Bob's answer together with my incorrect suggestion to use
>> string(1..B.L), which violates that rule; when you use a discriminant
>> in a constraint, the discriminant can't be an "expanded name" or part
>> of a larger expression, and I think B.L is an expanded name here.  My
>> apologies for misleading you.
>>
>> This should work:
>>
>>     type B (L : Natural) is new A(L) with record
>>          T : String (1 .. L);
>>     end record;
>>
>> Everything I said earlier about visibility wouldn't apply here,
>> because redeclaring the discriminant L makes it visible inside the
>> record declaration of B.  This would work too:
>>
>>     type B (Ell : Natural) is new A(L) with record
>>          T : String (1 .. Ell);
>>     end record;
>>
>> It's the new discriminant that can be used in the declaration, not the
>> one inherited from A.
>>
>> > Is my first code correct? I guess yes...
>>
>> Still no.  The compiler may accept it, but that just means the
>> compiler has a bug.
>>
>> I hope I've got everything straight now.
>>
>>                                    -- Adam
> --
> You are right !!  , it works :-)
> Thanks for all.
> Tony.
> --

Tony,

Thanks for bringing this problem to our attention.

Tom Grosman, Aonix 

Re: Discriminant ans tagged type ?!

[Robert A Duff]

Tony <truand.tony@gmail.com> writes:

> I just do not understand why the following code compiles with the Aonix
> compiler and not with the Gnat GPL 2007?
>
>     package A_Pkg is
>         type A (L : Natural) is tagged null record;
>     end A_Pkg;
>
>     package A_Pkg.B_Pkg is
>         type B is new A with record
>             T : String(1..L);
>         end record;
>     end A_Pkg.B_Pkg;
>
>     with A_Pkg.B_Pkg;
>     procedure Strange is
>     begin
>         null;
>     end Strange;
>
>    => RM95 3.7 (18) ??

There's 3.9.1(8), which is a NOTE.

If you want to do the above, you can say:

    type B (L : Natural) is new A(L) with ...

- Bob