Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!wasatch!cs.utexas.edu!uunet!mcvax!unido!gmdzi!kloppen
From: kloppen@gmdzi.UUCP (Jelske Kloppenburg)
Newsgroups: comp.lang.modula2
Subject: Re: Recursive data types
Summary: Recursive data types with the help of pointers
Message-ID: <1046@gmdzi.UUCP>
Date: 8 May 89 19:12:17 GMT
References: <5734@cs.Buffalo.EDU>
Organization: GMD, Sankt Augustin, F. R. Germany
Lines: 31

In article <5734@cs.Buffalo.EDU>, ugprussa@cs.Buffalo.EDU (Michal Prussak) writes:
> Wirth describes in his book "Algorithms and Data Structures" (from 1986)
> a recursive data type (p 173):
> 
> TYPE
>    ped = RECORD
> 	CASE known: BOOLEAN OF
> 	   TRUE: name: ARRAY[1..10] OF CHAR |
>            FALSE: father, mother: ped;   <--- recursive fields
>         END (* case *);
>    END (* record *);				
> 
> ...

That can not work. How much space should be reserved for a variable
of such a type? The world is not as big!
To generate recursive data structures I use the following:

TYPE
   LinkPTR = POINTER TO Link;
   Link = RECORD
             Text: String;
             Count: CARDINAL;
             Left, Right: LinkPTR
   END;

and I think a similar example is in Wirth's book defining modula.

              kloppenbrg@kmx.gmd.dbp.de
        UUCP: kloppen@gmdzi
In real life: Jelske Kloppenburg