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: 103376,38fc011071df5a27
X-Google-Attributes: gid103376,public
X-Google-ArrivalTime: 2003-06-25 20:03:00 PST
Path: archiver1.google.com!postnews1.google.com!not-for-mail
From: aek@vib.usr.pu.ru (Alexander Kopilovitch)
Newsgroups: comp.lang.ada
Subject: Re: Ideas for Ada 200X
Date: 25 Jun 2003 20:02:59 -0700
Organization: http://groups.google.com/
Message-ID: <e2e5731a.0306251902.6e8b3461@posting.google.com>
References: <uhe6zw201.fsf@nasa.gov> <AwvGa.1228118$F1.143267@sccrnsc04>
 <3EECA772.4B662024@adaworks.com> <hYmHa.6881$Hb.124073@news4.e.nsc.no>
 <BB13C10D.350A%yaldnifw@blueyonder.co.uk>
 <bcl1pu$jscm4$1@ID-175126.news.dfncis.de>
 <BB13CDB9.3516%yaldnifw@blueyonder.co.uk>
 <e2e5731a.0306180700.61b2575f@posting.google.com>
 <e2e5731a.0306191037.3addbae5@posting.google.com>
 <RpVJa.47832$JA5.837234@news.xtra.co.nz>
 <slrnbfg8vd.nq.lutz@taranis.iks-jena.de>
 <BB1FBF4A.3781%yaldnifw@blueyonder.co.uk>
NNTP-Posting-Host: 62.152.82.224
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 8bit
X-Trace: posting.google.com 1056596579 23891 127.0.0.1 (26 Jun 2003 03:03:00
 GMT)
X-Complaints-To: groups-abuse@google.com
NNTP-Posting-Date: 26 Jun 2003 03:03:00 GMT
Xref: archiver1.google.com comp.lang.ada:39758
Date: 2003-06-26T03:03:00+00:00
List-Id: <comp.lang.ada>

Bill Findlay wrote:

>On 24/6/03 11:11, in article slrnbfg8vd.nq.lutz@taranis.iks-jena.de, "Lutz
>Donnerhacke" <lutz@iks-jena.de> wrote:
>
>> * AG wrote:
>>> Seriously though, what's the (*) & X semantics?
>> 
>> The LHS 'X' is not evaluated twice to get the parameter a of the function "&".
>> For the parameter b of the same function "&", 'X' is evaluated a second time.
>>> Is X allowed to be a function returning some access value?
>> Yes.
>>> If so, will (*) require second call to the function (with potentially
>>> different result) or not?
>> (*) is required to NOT evaluate the LHS expression once more.
>> Furthermore this construct is required to evaluate the LHS expression before
>> any part of the RHS.
>
>I see the semantics of idem as being well described by the following (which
>would need much refinement before being precise enough for inclusion in a
>standard, of course):
>
>Let:
>
>   X  :=  f(idem);
>
>be equivalent to declaring the procedure:
>
>   procedure update_V_with_f (V : in out the_type_of_X) is
>   begin
>      V := f(V);
>   end ;
>
>in the environment of the assignment, and executing:
>
>    update_V_with_f (X);
>
>instead of the the assignment.
>
>Naturally, update_V_with_f is intended to be an unspellable identifier so
>that it cannot be called explicitly, etc, etc.

Just one slight change in the denotation -- for convenience of common folk -:)
- use "expr" unstead of "f", that is:

Let:

   X  :=  expr(idem);  -- "expr" for an expression

be equivalent to declaring the procedure:

   procedure update_V_with_expr (V : in out the_type_of_X) is
   begin
      V := expr(V);
   end ;

in the environment of the assignment, and executing:

    update_V_with_expr (X);

instead of the assignment.