Re: Ada vs Fortran for scientific applications

["Jan Vorbrüggen" <jvorbrueggen@not-mediasec.de>]

> Ah, but an unforeseen error is a bug. One cannot be bug-tolerant, it is
> self-contradictory, after all. Programming error (bug) means that the
> system's state is not adequate to the physical system. Which could be the
> rocket falling right onto the control tower. But that's no matter, because
> there is no way for the program to know anything about that. Once you start
> to judge about such undesired program states (even purely statistically),
> and change the program, they automatically become *foreseen*.

I don't consider that distinction helpful - it's like saying that economically
important algorithms are NP-complete and thus unsolveable, while experience
tells you that almost all practical problems turn out to be solveable with
polynomial algorithms or at least reach approximations to the optimal solution
that are economically indistinguishable.

It's similar to approaches people have in driving cars. On the one hand, you
can drive "defensively", i.e., you take into account that other participants
in traffic might not behave in an optimal way. Or you can drive agressively,
with the expactation that should somebody else suffer a momentary lapse of
concentration, say, you will have a crash.

Incidentally, I consider "graceful degradation" the hallmark of good engi-
neering, and the Ariane 501 design was anything but that. The control system
of your body, on the other hand, is the best known example of a system showing
this property.

	Jan