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Newsgroups: comp.lang.ada
Subject: Re: Generic Package
From: Georg Bauhaus <bauhaus@futureapps.de>
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Date: Tue, 01 May 2007 11:02:22 +0200
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Date: 2007-05-01T11:02:22+02:00
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On Mon, 2007-04-30 at 22:04 +0200, Dmitry A. Kazakov wrote:
>  It was that if foreach were a primitive operation
> defined on an unordered set, then its contract could not be stated.

Every specific Set object (collection of elements) inside a computer has
a memory layout. That is, for every specific set object there
exists an index set, the collection of addresses that maps elements
1:1 onto a set of pairwise disjoint natural numbers.

Since, I think, we are talking about computer representations of
sets, the fact of representation
 (1) establishes some order
 (2) hence allows arguing about First, ..., Foreach in terms of
     the general (and specifically unknown) properties of every
     representation.

For every finite set that doesn't fit into core memory,
use garbage collection (a job for the librarian you mentioned).
Define the element index number via a pair of numbers (time, address).
These, again, can be enumerated.

> To be able to pick a random member <=>
> to have an order.

Can you determine whether one of your sets is empty?