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Newsgroups: comp.lang.ada
Date: Tue, 29 Nov 2016 12:32:58 -0800 (PST)
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Subject: Re: Ada 2012 Constraints (WRT an Ada IR)
From: Shark8 <onewingedshark@gmail.com>
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Xref: news.eternal-september.org comp.lang.ada:32515
Date: 2016-11-29T12:32:58-08:00
List-Id: <comp.lang.ada>

On Tuesday, November 29, 2016 at 1:17:38 AM UTC-7, G.B. wrote:
> On 29.11.16 00:49, Shark8 wrote:
> > it certainly would be convenient if they were as then we could have an =
IR wherein the general form of a type-constraint is uniformly handled.
>=20
> The notes section of LRM 3.2.4 may be of interest here.
>=20
> Also, by way of extending the range of perspectives, maybe the
> added flexibility of predicates entails not only overlap but also
> separate handling. For example, being a positive (counting)
> number means being an integer greater than 0. So, conceptually,
> there is just one condition, not two as in a subtype constraint.
>=20
>=20
>     generic
>        type I is range <>;
>     package G is
>=20
>        subtype P is I with
>          Static_Predicate =3D> P > 0;
>=20
>     end G;
>=20
>=20
> --=20
> "HOTDOGS ARE NOT BOOKMARKS"
> Springfield Elementary teaching staff

Perhaps, but thinking about an IR, it seems like it would be nice to use Ad=
a's already implicit usage of sets more explicitly -- by which I mean thing=
s like CASE requiring every value in its type (i.e. the set of values in it=
s range) -- things like the "A predicate specification does not cause a sub=
type to be considered constrained." has no impact on delineating the set of=
 acceptable values. Example:

Type Serial_Number is new String
  with Dynamic_Predicate =3D> (for all Ch of Serial_Number =3D> Ch in '0'..=
'9';

The above has a constraint -- that of only holding digits -- but still is u=
nconstrained. If we were doing a formal CS class we'd say something like "T=
he type Serial_Number contains all strings that have only the decimal digit=
s therein." (Or somesuch, I'm borrowing from my memories of the class on DF=
As, NFAs, etc.)