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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: What is wrong with Ada?
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Date: Thu, 12 Apr 2007 22:41:50 +0200
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Date: 2007-04-12T22:41:00+02:00
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On 12 Apr 2007 19:54:05 GMT, Peter C. Chapin wrote:

>> But the number of program states is finite, or else the program is wrong
>> anyway?
> 
> In a Turing complete programming language it is possible to write programs 
> with unbounded amount of state. Indeed... this is the essence of Turing 
> completeness.
> 
> P.S. If I understand SPARK properly, the SPARK subset of Ada is not Turning 
> complete because for any given program there is a bound on how much state 
> information the program might use. As a result the halting problem is 
> decidable for SPARK programs. This is a consequence of the lack of dynamic 
> allocation and recursion. Of course useful programs can still be written 
> with SPARK despite its theoretical incompleteness. I imagine that making 
> SPARK less powerful than a Turing machine is the whole point of the 
> restrictions it imposes. Turing machines are hard to analyze.

Yes, one should give up some power for security.

This is why one should be suspicious to the arguments: "look how powerful
is the language feature X!"

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de