Re: Ariane 5 - not an exception?

[Ken Garlington <garlingtonke@lmtas.lmco.com>]

++ robin wrote:
> 
>         >  2) PL/I
> 
>         >     a) There is no PL/I compiler for the 1750A
> 
> ---Not an obstacle.  How was an Ada compiler written for it?

I believe an existing one was purchased. I don't believe an Ada
compiler was written specifically for the Ariane SRI, as apparently
you are suggesting be done for PL/I. How would your argument about
mature PL/I compliers stand up in the face of a requirement to 
develop a brand-new compiler for a new target?

> 
>         >     b) Ada is far more suitable for safety-sensitive software than Pl/I
> 
> ---Nonsense.  PL/I has a long (30 years) record in
> excellent real-time facilities, and with people with
> experience in error-recovery and fail-soft in routine
> commercial applications as well as real-time programming.

It must be the lag in these newsgroups. I've posted more than one
request in comp.lang.pl1 for some examples of PL/I's use in safety-critical
real-time flight software, and narya a taker yet. I look forward to
some examples...

Perhaps those people are too busy building such software to read
the Internet?

>         >     c) This failure was not a language issue.
> 
> ---Isn't it?  One of the arguments put forward was that
> an Ada condition couldn't be raised and leave a trace,
> and that it would be argued that there was no guarantee
> whether a piece of code was executed.

That argument could be put forth, but of course it would be false.
We routinely trace Ada 83 exceptions in our debugging environments.
Ada 95 also adds a standardized capability to annotate exceptions with
user-defined information.

>    In PL/I, a SIGNAL statement (which can be used for
> program checkout) leaves a printed record that it was
> executed.  It gives a message that the condition was
> raised, and comes with line numbers, etc.  There is
> absolutely no doubt that the statement did not execute!

There is no SIGNAL statement in PL/I. In fact, PL/I has no
exception handling capabilities. (I figure, since ++robin can
continue to ignore the capabilities of Ada, why shouldn't we
ignore his claims as to the capabilities of PL/I)?

As a side issue: Could someone post the printer port address for the
Ariane SRI? Most of our IRSs don't have a printer attachment.
Must be something those experienced PL/I programmers demand be
added to the hardware... :)

> 
>         > But
>         >     stupid management is something no programming language can change.
>         >     Given other engineering constraints on this project, Ada is really
>         >     the only reasonable language to choose.
> 
> ---Scarcely convincing, in view of the failure.

Again, I would be more convinced of _your_ arguments if you would post some
of the flight software items you've developed in PL/I. For some reason,
this request keeps getting lost in the newsgroup. Until then, I think I'll
just enjoy the speculation...

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