Re: Heartbleed

["Pascal J. Bourguignon" <pjb@informatimago.com>]

Simon Wright <simon@pushface.org> writes:

> "Pascal J. Bourguignon" <pjb@informatimago.com> writes:
>
>> But strongly late dynamically typed programming languages are probably
>> better for mission critical systems, since they can adapt dynamically
>> the type of the values at run-time, instead of crashing.
>
> If the system designers have thought about what to do under such
> circumstances so that the system can carry on, OK,
>
> If not, the system is operating outside its design envelope, which I
> think is equivalent to the Ada "erroneous behaviour; so you don't know
> _what_ it will do, and the best response is probably to fall back to a
> pre-planned recovery mode. Or, as you say, to crash; which has at least
> the virtue, during development, of making it obvious that there's a
> problem to be fixed.

The Ariane 5 and Mars Climate Orbiter are proof that this is not the
right methodology.  Those systems were specified, developed with crashes
and erroneous behaviour during development, and all bugs were obvious
(to the point of making big explosions).  Oops, too late!


There are life-or-death systems that needs to continue running, even in
a degrated mode, whatever happens, whatever bug they may still contain
once deployed. 

Statically checked, variable-typed languages aren't up to the job for
those systems.

There will always be bugs remaining, even in tested and more
importantly, even in proven software!  Cf. for example, the Deep Space 1
RAX software, written in Lisp, and proven!  Despite the proof, a bug
remained.  If it had been a statically checked programming language, it
would have meant a terminal dead-lock or a crash (what else to do with a
static language when we reach a state that has been proved impossible?).
But since it was a dynamic programming language, (with very late
binding, including a on-board compiler), it was debugged and patched
remotely, as a last ressort solution.


-- 
__Pascal Bourguignon__
http://www.informatimago.com/
"Le mercure monte ?  C'est le moment d'acheter !"