Re: Community Input for the Maintenance and Revision of the Ada Programming Language

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On 2017-09-08 23:04, Johan Söderlind Åström wrote:

> I would really like to write, for a example:
>    (A (I) + B (I)) * C (I) / (D (I) ** E (I));
> instead of:
>    (A (A'First + I) + B (B'First + I)) * C (C'First + I) / (D (D'First + I) ** E (E'First + I));
> ... you know for obvious reason.

Since these things are usually happen in a loop the compiler might have 
issues with eliminating index checks. Because you would replace

    for I in A'Range loop
       ... (A (I) + B (I)) * C (I) / (D (I) ** E (I)) ...
    end loop;

with

    for I in 0..A'Length - 1 loop
       ... (A (I) + B (I)) * C (I) / (D (I) ** E (I)) ...
    end loop;

BTW, the code usually looks even uglier:

    for I in A'Range loop
       ... (A (I) + B (I + B'First - A'First)) *
           C (I + C'First - A'First) / (D (I + D'First - A'First) **
           E (I + E'First - A'First)) ...
    end loop;

However, it is easier to optimize, I guess.

To me it is the loop, which should have a form to walk through several 
congruent arrays. E.g. using conventional mathematical notation:

    for I,J,K,L,M in A'Range,B'Range,C'Range,D'Range,E'Range loop
       ... (A (I) + B (J)) * C (K) / (D (L) ** E (M)) ...
    end loop;

Positional indexing is another issue. Position /= index. Position is 
always an ordinal number. It is the same type for all array types. Array 
index is any discrete type, not necessarily integer, and maybe specific 
for each array type.

Ordinal numbers can be used for indexing using S'Val () attribute where 
S is the array index subtype. It is extremely ugly but useful when the 
array index type is not numeric.

I am for adding positional array element access. But it must have a 
clearly distinct syntax. E.g. either by using square brackets:

    A [Position]

or per attribute:

    A'Nth (Position)

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de