Re: What is wrong with Ada?

[Markus E Leypold <development-2006-8ecbb5cc8aREMOVETHIS@ANDTHATm-e-leypold.de>]

Robert A Duff <bobduff@shell01.TheWorld.com> writes:

> Markus E Leypold
> <development-2006-8ecbb5cc8aREMOVETHIS@ANDTHATm-e-leypold.de> writes:
>
>> But the set of all inputs is not necessarily finite -- i.e. in the
>> case that the user might enter one data item after the other and get
>> some answer about that item until he enters a end-of-input symbol
>> (stupid example: an interactive prime tester). Since it is nonsense to
>> artificially restrict the length of the user interaction just to get a
>> finite set of input sequences, we will have to live with a infinite
>> number of potential inputs to the program. So the paths covered are
>> also inifinite (program state is still finite since the machine has
>> only finite state).
>
> Yes.  But I want to know that my program will work properly on any
> computer, including ones that don't exist yet.  I don't know how big or
> fast computers will be in ten years.  That's why it's useful to reason
> about computers that have unbounded amounts of memory (and time!) --
> e.g. Turing machines -- even though we will never be able to build
> such a thing.

Of course. That's another aspect I left out, because first I wanted to
deal with Dmitry's misconception that real or correct programs can
only have finite sets of possible input, thus exhaustive testing would
always be possible, but "only" impractical. Instead of arguing about
(non existent) inifinite machines (and I agree with your view that
reasoning about them is useful, but I know how far I come when
discussing non-existent theoretical constructs with Dmitry :-( ), I
decided to topple this hous of cards by pointing out that even finite
machines can process inputs from infinite sets. 

So sorry, in a sense you're barking up the wrong tree, since it wasn't
me who called inifinite machines useless or only theoretical (that was
Dmitry).

:-)

Regards -- Markus