From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.5-pre1 (2020-06-20) on
	ip-172-31-74-118.ec2.internal
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=3.0 tests=BAYES_00 autolearn=ham
	autolearn_force=no version=3.4.5-pre1
Path: eternal-september.org!reader02.eternal-september.org!aioe.org!5WHqCw2XxjHb2npjM9GYbw.user.gioia.aioe.org.POSTED!not-for-mail
From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: array from static predicate on enumerated type
Date: Fri, 12 Mar 2021 23:41:53 +0100
Organization: Aioe.org NNTP Server
Message-ID: <s2gqnf$vbs$1@gioia.aioe.org>
References: <89128f73-fcc5-4e57-8067-d09877ba0211n@googlegroups.com>
NNTP-Posting-Host: 5WHqCw2XxjHb2npjM9GYbw.user.gioia.aioe.org
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
X-Complaints-To: abuse@aioe.org
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101
 Thunderbird/78.8.1
Content-Language: en-US
X-Notice: Filtered by postfilter v. 0.9.2
Xref: reader02.eternal-september.org comp.lang.ada:61506
List-Id: <comp.lang.ada>

On 2021-03-12 21:49, Matt Borchers wrote:
> Say, for example, I define a static predicate on a sub-type of an enumerated type, like:
> 
> type LETTERS is ( A, B, C, D, E, F, G, H, I , J, K );
> 
> subtype CURVED is LETTERS
>      with Static_Predicate CURVED in B | C | D | G | J;

Do not use this thing, because its semantic is basically a lie as it 
violates contracts of other operations of the type, like 'Succ.

Using formal speak, CURVED is not substitutable for LETTERS in too many 
cases to be any useful.

This applies to any arbitrary constraints you could impose using a 
predicate. They break things. Do not ever consider them as an option.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de