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,a59300e1cca1082c
X-Google-Attributes: gid103376,public
X-Google-ArrivalTime: 2001-09-20 04:37:58 PST
Path: 
 archiver1.google.com!newsfeed.google.com!newsfeed.stanford.edu!news.tele.dk!small.news.tele.dk!195.158.233.21!news1.ebone.net!news.ebone.net!news.net.uni-c.dk!not-for-mail
From: Jacob Sparre Andersen <sparre@nbi.dk>
Newsgroups: comp.lang.ada
Subject: Parametrically polymorphic operations (Was: Safe C++)
Date: Thu, 20 Sep 2001 13:37:57 +0200
Organization: Centre for Chaos and Turbulence Studies, Niels Bohr Institute
Message-ID: <3BA9D515.1E6C7A49@nbi.dk>
References: <3BA7A45D.186EE27A@adaworks.com>
 <20010919072904.O10277-100000@shell5.ba.best.com>
 <Pine.GSO.4.31.0109191143280.19438-100000@sens-a.cse.msu.edu>
 <20010919102107.L4954-100000@shell5.ba.best.com>
 <9ob2u6$2r4l$1@msunews.cl.msu.edu>
NNTP-Posting-Host: alf.nbi.dk
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
X-Trace: news.net.uni-c.dk 1000985877 13128 130.225.212.55 (20 Sep 2001
 11:37:57 GMT)
X-Complaints-To: usenet@news.net.uni-c.dk
NNTP-Posting-Date: Thu, 20 Sep 2001 11:37:57 +0000 (UTC)
X-Mailer: Mozilla 4.78 [en] (X11; U; OSF1 V4.0 alpha)
X-Accept-Language: fo,da,no,sv,is,de,fr,en
Xref: archiver1.google.com comp.lang.ada:13205
Date: 2001-09-20T13:37:57+02:00
List-Id: <comp.lang.ada>

Chad:

> "Brian Rogoff" <bpr@shell5.ba.best.com> wrote in message
[...]
> > Parametrically polymorphic functions

> I'll have to trust you or these three since I have never encountered a
> situation where I was ever wishing for such functionality.

While working on libraries for matrix operations and unit
safe types, I have certainly wanted something very similar
to parametrically polymorphic functions. It would make it
possible to have more extensive compile time checks, than
what is possible with Ada as it is defined today.

An example:

   type Matrix (Left, Right : Positive) is private;

   function "*" (Left  : in Matrix;
                 Right : in Matrix (Height => Left.Width))
     return Matrix (Width  => Right.Width,
                    Height => Left.Height);

(I hope the intention is clear although the syntax isn't
defined)

This would tell the compiler a few things, which would allow
it to
flag type mismatches already at compile time.

The current Ada specification forces us to move these checks
into the body of the functions and procedures.

Jacob
-- 
"an OS that is almost, but not quite, entirely unlike
Windows"