From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
	ip-172-31-65-14.ec2.internal
X-Spam-Level: 
X-Spam-Status: No, score=-3.2 required=3.0 tests=BAYES_00,NICE_REPLY_A,
	T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6
Path: eternal-september.org!reader01.eternal-september.org!.POSTED!not-for-mail
From: "Jeffrey R.Carter" <spam.jrcarter.not@spam.acm.org.not>
Newsgroups: comp.lang.ada
Subject: Re: New aggregates with Ada 2022.
Date: Wed, 29 Jun 2022 10:30:20 +0200
Organization: A noiseless patient Spider
Message-ID: <t9h2is$1ckn5$1@dont-email.me>
References: <t8ml0l$1vo2$1@gioia.aioe.org> <t8qptm$gof$2@dont-email.me>
 <t8qrmo$p79$1@gioia.aioe.org> <t8tk6i$ue6$1@dont-email.me>
 <t8ulu9$jca$1@gioia.aioe.org> <t90ebe$nve$1@dont-email.me>
 <t91buq$10im$1@gioia.aioe.org> <t933oh$o2o$1@dont-email.me>
 <t93mr6$pvm$1@gioia.aioe.org> <t95uha$edq$1@dont-email.me>
 <t96i9f$1mc1$1@gioia.aioe.org> <t9d7u5$ogle$1@dont-email.me>
 <jhviamFe72sU1@mid.individual.net> <t9gir4$1bbuh$1@dont-email.me>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Injection-Date: Wed, 29 Jun 2022 08:30:20 -0000 (UTC)
Injection-Info: reader01.eternal-september.org; posting-host="f0eedd88e4429dcbcad6ebcd7d070c13";
	logging-data="1463013"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX19fBbxNSGHuV5AHCrwTBgkp9rgkVZvAY2k="
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.9.1
Cancel-Lock: sha1:bPqn9RUll/rz8uuiz1VCc7EkUEw=
In-Reply-To: <t9gir4$1bbuh$1@dont-email.me>
Content-Language: en-US
Xref: reader01.eternal-september.org comp.lang.ada:64048
List-Id: <comp.lang.ada>

On 2022-06-29 06:01, Randy Brukardt wrote:
> 
> But there is (or shouldn't be) anything special about a one-dimensional
> array (presuming you intend to allow arrays with more dimensions). And the
> "abstraction" you talk about is selecting a bunch of barely related elements
> from a multi-dimensional array.

Arrays are usually used to implement map, (mathematical) matrices and vectors, 
or sequences. Each usage tends to have unique features:

* Maps are usually constrained. It does not make sense to concatenate, sort, 
slice, or slide a map. The abstraction of a map includes non-discrete key 
subtypes, so arrays used as maps are a special case.

* Matrices have component types that behave like numbers. The mathematical 
definition of matrices includes integer indices with a lower bound of 1. Vectors 
are usually considered to be matrices of one column ("column vector") which can 
be transposed to obtain matrices of one row ("row vector").

* Sequences are usually unconstrained. Typical discussion of sequences outside 
of programming use integer values to indicate positions, using terms such as the 
first thing in a sequence, the second thing, ..., so indices should be of an 
integer type with a lower bound of 1. It sometimes makes sense to concatenate, 
sort, slice, or slide sequences.

A language that provided direct support for these abstractions should not need 
to provide arrays.

-- 
Jeff Carter
"[T]he language [Ada] incorporates many excellent structural
features which have proved their value in many precursor
languages ..."
C. A. R. Hoare
180