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Date: Mon, 25 Jun 2012 14:39:06 +0200
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Subject: Re: about the new Ada 2012 pre/post conditions
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Date: 2012-06-25T14:39:07+02:00
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On 25.06.12 13:54, Dmitry A. Kazakov wrote:

>> Indeed, it helps to remember that logicians and mathematicians
>> have learned that logic and mathematics cannot justify themselves.
> 
> No, they never ever did that.

They tried, though. I didn't even say that they did.

Frege thought, for some time, that he had done.
Russel sent a correction. Hilbert did not give up, though:

http://en.wikipedia.org/wiki/File:HilbertGrab.jpg

 WIR M�SSEN WISSEN
 WIR WERDEN WISSEN

Optimism!

>> We have to do something. DbC is something. Better than nothing.
> 
> Is SPARK nothing?

Try

 new Data'(Size => More_than_4k);

> Is strong typing nothing?

Until Ada 2012, there was nothing in addition to the strong type
system of Ada 2005.

> But you seemingly did not read what I wrote earlier. There is either #1 or
> #2.

I have tried to explain that neither #1 nor #2 are applicable
because they assume applicability of exhaustive formal analysis
to general program design (not programs). Wrong frame of reference.

DbC does not claim to be a replacement for a type system.

>> DbC is a best effort thing like every system building effort.
> 
> How are you going to prove this, if "DbC" contradicts logic itself?

A program that is known to be covered entirely by logic
is really an exception. Its notion, however, sells and is
a good, justifiable tool in political rhetoric, IMHO.

Proving things in a DbC framework is similar to proving things
with the help of more than Ada, as is done when using SPARK.
If we can't have a more proof friendly type system, let's have
at least aspects. Proofs isn't everything. Writing programs
for system is.