Re: Real syntax problems in Ada

["Vasiliy Molostov" <molostoff@gmail.com>]

Dmitry A. Kazakov <mailbox@dmitry-kazakov.de> писал(а) в своём письме Tue,  
28 Aug 2012 19:23:42 +0400:

> a symmetric declaration of a procedure would be:
>
>    X : procedure :=
>       begin
>          ...
>       end X;

mnmn. where to apply parameter list declaration (suppose this as procedure  
type "constraint")?

instead of subprogram access types we have objects in itself, how to  
operate them? and ":=" is a re-definable construct, as I remember, while  
we can not express operations on sub-program body. How about to implement  
simple "<", ">" for sub-program bodies? hehe.

I am not sure that it is appropriate.

>    Diag : Matrix :=
>        ( 1 => (1 => 1.0, others => 0.0),
>          2 => (2 => 1.0, others => 0.0),
>          3 => (3 => 1.0, others => 0.0));

Yep, agree, it would be very helpful for multidims, but indeed the type of  
"(1 => 1.0, others => 0.0)" is unknown (anonymous), we can not cast  
already prepared objects (aka tmp := (1 => 1.0, others => 0.0)) to supply  
to this construct. So as a result this one  is useless without referencing  
another variable or constant in this constraint.

How about "(T'(1..1, 1..1 | 2..2) => 1, others => 0)"? And what type of T  
should be here?

> type T is abstract tagged limited null record; -- Only so
>
> type T is abstract limited tagged null record; -- Illegal
> type T is limited tagged abstract null record; -- Illegal
> ...
>
> I bet very few would remember the proper order if asked unprepared.

I remember very well, since it is only one order can be (and only one I  
should remember), and this can be considered as simplicity. Other variants  
can break eye on looking for similar constructs while they are just in  
another order, no benefit, useless.

> Luckily
> GNAT would advise how to reorder the keywords in its error message.

if this is for error message only, I can agree, but the rule is real when  
it is stable for a long time (e.g. unchanged). e.g. much better to have it  
as an error.

Gnat and lucky? Hmmm.

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