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From: stt@houdini.camb.inmet.com (Tucker Taft)
Subject: Re: Doubly linked list.
Date: 1998/12/15
Message-ID: <F40rpJ.5yB.0.-s@inmet.camb.inmet.com>#1/1
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References: <7560vn$21e@romeo.logica.co.uk>
Organization: Intermetrics, Inc.
Newsgroups: comp.lang.ada
Date: 1998-12-15T00:00:00+00:00
List-Id: <comp.lang.ada>

Matt Tyler (matt_tyler@hotmail.com) wrote:

: I'm having trouble implementing a Doubly linked list in ada.

: My procedure to add a new singly linked record to the list is (body only)

: List:=new Box'(V,List);

: where V is an integer and List is an access type to box.

: I don't understand how to set another access type in the record to the
: previous record on the list. Can anyone help??

With a doubly linked list, each list element has both a "next" and
a "prev" component, in general.   You need to initialize both.  In
general, one will be null in the new element.

The following will accomplish the job:

    -- Insert on front of list
    List := new Box'(V, Next => List, Prev => null);  

    if List.Next /= null then
        -- Make old "first" element point back to new "first"
        List.Next.Prev := List;  
    end if;

: P.S is there a comp.lang.ada faq ???????????

Try www.adahome.com.

: Cheers,

: Matt Tyler

--
-Tucker Taft   stt@averstar.com   http://www.averstar.com/~stt/
Technical Director, Intermetrics, Inc.  Burlington, MA  USA
An AverStar Company (www.averstar.com)