Re: Little people supporting Ada, possibly through AdaCore?

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Thu, 19 Jul 2012 00:45:19 -0700 (PDT), Maciej Sobczak wrote:

> W dniu �roda, 18 lipca 2012 19:14:35 UTC+2 u�ytkownik Dmitry A. Kazakov napisa�:
> 
>> True. However a set of truly unordered elements cannot be implemented
>> otherwise than on top of an ordered set.
> 
> Why?

I guess it is related to computability.

>> E.g. to be able to implement membership test.
> 
> Membership test does not require any order.

You need to enumerate elements to be able to compute it. Enumeration is
equivalent to ordering.

>> It is interesting to speculate about the interface of an unordered set such
>> that the clients could not exploit its ad-hoc order.
> 
> Make it... parallel?
> You know, instead of relying on sequential algorithms try to think in
> terms similar to those in ParaSail. Membership test is a question asked to
> multiple tasks (representing subsets or even individual elements from the
> domain), where at most one of them will answer "yes".

That confuses mutability and membership. Or do you suggest something like
Monte Carlo performed by a bunch of tasks? In that case you would need to
identify elements in the set in order to compare them with the testee. That
again would require some order.
 
> Inefficient? This depends on the hardware - our current hardware is
> sequential in nature where parallelism is an afterthought, but take
> molecular computing into account and things start to look a lot different.

Yep, as I said, it must be related to computability. A hardware may provide
sets incomputable programmatically. These could be unordered. E.g. it could
ask you if X belongs to S.

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