Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!zephyr.ens.tek.com!tektronix!nosun!qiclab!m2xenix!puddle!p3.f18.n114.z1.fidonet.org!Chip.Richards
From: Chip.Richards@p3.f18.n114.z1.fidonet.org (Chip Richards)
Newsgroups: comp.lang.modula2
Subject: Re: Implementing Abstract Lists
Message-ID: <224.26BF133D@puddle.fidonet.org>
Date: 6 Aug 90 02:25:27 GMT
Sender: ufgate@puddle.fidonet.org (newsout1.26)
Organization: FidoNet node 1:114/18.3 - Iasd Eng Bbs, Phoenix Az
Lines: 35


In a message dated 1 Aug 90, dgil@pa.reuter.COM (Dave Gillett) wrote:

 > So I was severely disappointed to discover that the "List" module presented 
 > does not in fact deal with lists in the abstract, but with lists of things 
 > of type "ItemType" which is imported from some other module.  So in a 
 > typical real-world program, if I have three types of things that I want 
 > lists of, I need three (almost but not quite identical) copies of the List 
 > module as presented. 

Umm, gee, Dave, maybe I'm missing the point, here, but isn't this where a variant record would come in real handy?  As in

TYPE
   ThingType = ( aThing, anotherThing, lastThing ) ;
   ItemType = RECORD
      CASE ThingType OF
         aThing:
            fields for a thing
            |
         anotherThing:
            fields for another thing
            |
         lastThing:
            fields for last thing
      END  (* case *)
   END ;

Maybe I just misunderstood your problem, but using the above definition, one copy of the "List" module would handle three widely different types of things.

Chip


--  
uucp: uunet!m2xenix!puddle!114!18.3!Chip.Richards
Internet: Chip.Richards@p3.f18.n114.z1.fidonet.org