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=unavailable autolearn_force=no version=3.4.4
Path: 
 eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!.POSTED!not-for-mail
From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: grassroots thoughts on access types
Date: Sat, 10 Feb 2018 14:02:24 +0000
Organization: A noiseless patient Spider
Message-ID: <lyfu69lz7z.fsf@pushface.org>
References: <5d9134c9-a7d4-468e-8685-ebbb393eabea@googlegroups.com>
	<p5kk5i$5fj$1@dont-email.me> <p5kl6u$12m5$1@gioia.aioe.org>
	<p5krq3$103$1@dont-email.me> <wcck1vlex4t.fsf@TheWorld.com>
	<p5l4nl$4hm$1@dont-email.me> <p5l60c$ol$1@gioia.aioe.org>
	<e6ab5614-74af-41e1-804c-dec1b84b449c@googlegroups.com>
	<13f51bd1-00ef-4d2a-94b9-2d2560b449f3@googlegroups.com>
	<7781f82a-7df3-4f00-9bc8-ee60c24311f6@googlegroups.com>
Mime-Version: 1.0
Content-Type: text/plain
Injection-Info: reader02.eternal-september.org;
 posting-host="3f0772393081e6fad0b3e0b589a62a8b";
	logging-data="5873"; mail-complaints-to="abuse@eternal-september.org";
	posting-account="U2FsdGVkX1+EKEdjQqeLoPknGVM2fOE0s9Do4Q1cKJ0="
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.3 (darwin)
Cancel-Lock: sha1:p8UKbN1/AK3GGgBaJ9dp3dab4I4=
	sha1:5CroZ4DBwtqsFidefWK4MmQa+OY=
Xref: reader02.eternal-september.org comp.lang.ada:50367
Date: 2018-02-10T14:02:24+00:00
List-Id: <comp.lang.ada>

Mehdi Saada <00120260a@gmail.com> writes:

> while we're at it, how would I write in SPARK
> type Cell is
>    record
>       Next: access Cell;
>       Value: Integer;
>    end record;

You might implement the container as an array, and the Next field would
be an index into the array (or some 'end of list' marker).

   type Base is range 0 .. N;
   subtype Index is Base range 1 .. Base'Last;
   End_Of_List : constant Base := 0;

   type Cell is record
      Next : Base := End_Of_List;
      Value : Integer;
   end record;

   type List is record
      Head : Base := End_Of_List;
      Contents : array (Index) of Cell;
   end record;