Re: Ariane5 FAQ

[aek@vib.usr.pu.ru (Alexander Kopilovitch)]

Hyman Rosen wrote:

>one of the things I do is correct misstatements about that language.
>Another thing I like to do is to point out places where Ada afficionados
>have, in my opinion, too high an opinion of themselves or their language.

Well, so why didn't you exploit a direct oppotunity for that in Ariane 5
crash case?

You must know well that one thing Ada advocates are proud of is Ada's
capability to carry more information about programmer's intentions
and decisions directly in  source code than other general-purpose
programming languages. It means that with Ada lesser part of such 
information need comments to be expressed clearly.

At the same time both official report and c.l.a. discussions tell you that
the critical point from which the actual low-level chain of events started
was that the limitations for some variables that were not reflected in
comments (although were described in documentation). And that this
misled the developers of the simulator which was used for rocket's
testing instead of real device.

But those limitations should be very simple and fundamental kind of
information about programmer's intentions and decisions. So, if the
above claims are right then that information must be in source code,
not in comments, and if it were there then the simulator's developers
had no chance to miss it. There should be something like RANGE qualifier,
no more. Yes, one can say that RANGE will imply unwanted check, but
once more, there should be a pragma, which suppresses that check.
So, combination of RANGE and pragma will clearly convey the intentions,
both to compiler and to another programmer.

With those statements you can conclude that either Ada language is not
so greate in this aspect as some people claim or there was some
programmer's fault -- if the present language feature was not used properly.
(Only possible escape is that it was Ada 83, and the missed feature was
added later - for Ada 95 or even later).

Good opportunity, isn't it? -:)



Alexander Kopilovitch                      aek@vib.usr.pu.ru
Saint-Petersburg
Russia