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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: class wide iterable (and indexable)
Date: Tue, 29 Jan 2019 01:45:26 -0600
Organization: JSA Research & Innovation
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Xref: reader01.eternal-september.org comp.lang.ada:55396
Date: 2019-01-29T01:45:26-06:00
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"Shark8" <onewingedshark@gmail.com> wrote in message
news:f4c1e192-9a24-40d1-abd1-233ef6087658@googlegroups.com...
> On Wednesday, January 23, 2019 at 3:47:43 PM UTC-7, Randy Brukardt wrote:
>> "Shark8" wrote in message
>> news:9eedf818-8bfb-465b-afe5-aa3fb0525948...
>> > Wouldn't this be a non-issue if we could Static_Predicate Array-types
>> > like
>> > so?
>> >
>> > Type Some_String is Array(Positive range <>) of Character
>> >  with Static-Predicate => Some_String'First = 1;
>>
>> The idea of a static predicate is for them to stand-in for proper set
>> constraints (I would have preferred the latter, but I was alone on that),
>> so
>> they don't have anything to do with array bounds.
>
> What do you mean by "proper set constraints"? [And how would they look?]
> Things like {x| x in {2**y where y in 0..15} }? (X in
> 1|2|4|8|16|..|32_768)

See AI05-0153-2. The idea was that there was a kind of constraint that
represented a set. I used "when" in the syntax to reflect a case statement
limb:

    subtype Odd is Natural when 1|3|5|7|9;

The main difference semantically from static predicates was that these
actually changed the value set, which eliminated (at least in my mind) the
oddities with 'First and 'Last that occur for predicates. Otherwise, their
pretty much the same (including the banning of arrays and slices to
eliminate discontiguous arrays).

I was pretty much a group of one with this idea, so the AI was never really
vetted. So don't trust it too much.

                       Randy.

[Sorry about breaking the thread, I got a bunch of header errors when 
attempting to send a reply.]