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From: "Chad  R. Meiners" <chad.rmeiners@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: What is wrong with Ada?
Date: 14 Apr 2007 12:56:57 -0700
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Date: 2007-04-14T12:56:57-07:00
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On Apr 12, 3:54 pm, "Peter C. Chapin" <pcha...@sover.net> 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.

And you are correct in this.

> 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.

Turing machines, <b>in general</b>, are hard to analyze; the point is
to try to find a subset of Turing machines that are <b>useful</b> and
<b>easy to analyze</b>.