Re: Heartbleed

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

"Nasser M. Abbasi" <nma@12000.org> writes:

> On 4/12/2014 6:42 AM, Pascal J. Bourguignon wrote:
>> "Nasser M. Abbasi" <nma@12000.org> writes:
>>
>>> Python also is weakly typed.
>>
>> You're wrong.  Compare:
>
> How can I be wrong when in Python variables do not even have
> types, only values do.
>
> But any way, I was comparing it to Ada strong variable type
> system.  

That's the whole point.  

Typing values instead of typing variables is stronger.

When you have a system where all the values are typed, if there's a bug
(either because the language allows unsafe operations, or because
there's a bug in the system, or because there's a hardware failure), you
still have the assurance that only operations valid for this type of
value can be applied to it.

And the specific operation applied is dispatched at run-time, depending
on the type of value we encounter at run-time.  





>>>> a=float(1);
>>>> b=int(1);
>>>> c=a+b;
>
> The above will not even compile in Ada. Mixing apples and
> oranges.
>
> Python is not a language I would use to write robust
> software that if failed, people can die as a result. Lets
> leave it here.

IIRC, Ariane 5 software was written in Ada.
http://www.di.unito.it/~damiani/ariane5rep.html
In a language like lisp or python, the arithmetic operations that can't
produce fixnums automatically produce bignums, and all the code will
automatically handle bignums once the magnitudes require them.

Similarly, the Mars Climate Orbiter bug occured in statically typed
programming language: variables containing different units were still of
the same floating point data type.  
http://en.wikipedia.org/wiki/Mars_Climate_Orbiter#Cause_of_failure

A dynamically strongly typed-value programming language such as Lisp or
Python would have used objects containing both the magnitude and the
unit, and an operation mixing objects of different units would have
involved an automatic unit conversion.


In both cases, the customer could still consider that a bug exist (in
the case of Ariane 5 it was a specification "bug", so…), in that
operations could become slower than expected, but with  dynamically
typed-value system, you would still get correct results.  And in a
control system, it is better to generate correct control commands at
half the expected rate, than to crash or produce  bad control commands
at the initially specified rate.


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