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From: Niklas Holsti <niklas.holsti@tidorum.invalid>
Newsgroups: comp.lang.ada
Subject: Re: Heartbleed
Date: Sat, 12 Apr 2014 23:57:14 +0200
Organization: Tidorum Ltd
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Date: 2014-04-12T23:57:14+02:00
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On 14-04-12 20:56 , Pascal J. Bourguignon wrote:
> 
> IIRC, Ariane 5 software was written in Ada.

Still is, I believe, but irrelevant to the failure AIUI.

> 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.

But, as I understand it, that out-of-range value was then to be put into
some HW or telemetry field with a fixed size; the bignum would have to
be converted to a fixnum; the out-of-range error would happen (one
hopes), and there we are again.

> 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.

Except that the data were produced in one program and then given as
input to another program, breaking the type-checking chain.

Moreover, I don't see how you can be sure that a Lisp or Python
implementation *would* have used run-time unit tags. And finally, as
GNAT now shows, unit checking can be done statically with types, which
is always IMO better for this kind of systems.

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
      .      @       .