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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Ada 2012 Constraints (WRT an Ada IR)
Date: Mon, 19 Dec 2016 16:33:07 -0600
Organization: JSA Research & Innovation
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Xref: news.eternal-september.org comp.lang.ada:32914
Date: 2016-12-19T16:33:07-06:00
List-Id: <comp.lang.ada>

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
news:o32vjg$1jv4$1@gioia.aioe.org...
> On 2016-12-16 20:51, Randy Brukardt wrote:
...
>> The path was that set by Ada 83 with the idea of constraints. By your 
>> model,
>> constraint checks belong to the implementation, and those have always 
>> been
>> exposed in the specification.
>
> Not explicitly. It is like the implementation of "+" when an integer type 
> declared. The implementation is assumed but not specified.

Explicitly, by the semantic model I quoted earlier.

>> Later versions of Ada have just built on this
>> already existing (and very successful) idea, extending it to further 
>> cases.
>
> I meant explicit code snippets in declarations, which includes "is null", 
> checks, etc.
>
> It is very different from having type operations producing new [sub]types 
> like
>
>    subtype Y is X range 1..100;
>
> or
>
>    type T is array (I) of E;
>
> They declare and implement operations implicitly.

Only in your world-view, not the official Ada semantics, for a subtype. 
Operations are only declared for a type, not a subtype (and the location of 
declaration matters).

And I'm not sure why
    subtype Y is X range 1 .. 100;
is OK and
    subtype Z is X with Static_Predicate => Z > 0;
is not. They both have explicit declarations of the subtype, and the 
semantics is effectively the same.

                              Randy.