From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00 autolearn=ham
	autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,3e5f85a85cdab16e
X-Google-Attributes: gid103376,public
X-Google-ArrivalTime: 2001-03-22 08:59:20 PST
Newsgroups: comp.lang.ada
Path: 
 supernews.google.com!sn-xit-02!supernews.com!news.tele.dk!194.42.224.136!diablo.netcom.net.uk!netcom.net.uk!easynet-monga!easynet-tele!easynet.net!newspump.sol.net!nntp.msen.com!uunet!ash.uu.net!world!bobduff
From: Robert A Duff <bobduff@world.std.com>
Subject: Re: Should this be legal?
Sender: bobduff@world.std.com (Robert A Duff)
Message-ID: <wccn1adg32g.fsf@world.std.com>
Date: Thu, 22 Mar 2001 16:51:03 GMT
References: <99cjt2$v9g@newsserv.vs.dasa.de>
	<gLpu6.602532$U46.18328780@news1.sttls1.wa.home.com>
Organization: The World Public Access UNIX, Brookline, MA
X-Newsreader: Gnus v5.3/Emacs 19.34
Xref: supernews.google.com comp.lang.ada:6000
Date: 2001-03-22T16:51:03+00:00
List-Id: <comp.lang.ada>

"Mark Lundquist" <mark@rational.com> writes:

> I believe your completion of type Derived is legal, but I'm not a language
> lawyer... 

I *am* a language lawyer, but I don't know the right answer.
I would have to go study the conformance rules.

>...However, it seems like all the completion rules in 7.3 would
> really be unnecessary if the partial and full views were required to "look
> the same"...

But we don't want them to *be* the same.  Eg:

    type T is new Ancestor with private;
private
    type T is new Parent with record ...

is legal (and useful), if Parent is derived from Ancestor.

> > But then, if Base_2 and Base(2) are supposedly interchangeable,
> > how come the function Legal is accepted but function Illegal is
> > refused ("constraint not allowed here") ?
> 
> Because the construct that follows the "return" must be a subtype_mark, that
> is, a name that denotes a (named) subtype (i.e. either the "first subtype"
> of a type, or a subtype defined by a subtype declaration).  What you have
> there is actually just a syntax error.

Right -- it's just a syntax error.  But Oliver Kellogg asked *why*.  I'm
not sure, but an early version of Ada (1981?) allowed it.  Probably
something to do with when the expressions are elaborated.

- Bob