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From: "G.B." <bauhaus@notmyhomepage.invalid>
Newsgroups: comp.lang.ada
Subject: Re: Ada 2012 Constraints (WRT an Ada IR)
Date: Thu, 22 Dec 2016 10:54:29 +0100
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Xref: news.eternal-september.org comp.lang.ada:32942
Date: 2016-12-22T10:54:29+01:00
List-Id: <comp.lang.ada>

On 21/12/2016 22:15, Dmitry A. Kazakov wrote:

> There is a far better and safer model to produce user-defined subtypes that this mess.

Can you, please, show one?


>>> That would produce non-sets.
>>
>> At compile time? Otherwise, how can a specification of membership by
>> any Boolean function "produce" anything but that decision, if it does
>> compute a result?
>
> When predicate is not a complete function of the argument, e.g.
>
>    P (x) = (Integer (Clock - Epoch) mod 2) = 1

   Dynamic_Predicate => ... as you specified ...

produces a set, however random; this is predictable. Just like
before in older Ada, i.e., to the extent that the set of a range
constraint on S is predictable in

    procedure ... (N : Integer) is
       subtype S is Natural range 2 .. N;

Your Clock base membership stest will be more involved, whatever its
purpose might  be. It will compute a Boolean result, as long as the
inputs allow. See below.

>  Engineers insisting that 2+2=5 or doing things because the spirit of Napoleon told them so are to be fired and probably sent to medical examination.

Why does 2+2=5 apply when from a static predicate, but not when
from an Ada expression in general?