Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!boulder!sunybcs!ugprussa
From: ugprussa@cs.Buffalo.EDU (Michal Prussak)
Newsgroups: comp.lang.modula2
Subject: Recursive data types
Message-ID: <5734@cs.Buffalo.EDU>
Date: 7 May 89 19:39:06 GMT
Sender: nobody@cs.Buffalo.EDU
Reply-To: ugprussa@cs.Buffalo.EDU (Michal Prussak)
Organization: SUNY/Buffalo Computer Science
Lines: 28

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 *);				

He remarks that CASE construction must be used because IF is not available
in Modula. I would therefore think that it should be legal. I can imagine
it would be very difficult to compile, and not surprisingly none of the
compilers i have access to does not allow this (one of them is LOGITECH
from Frankfurt University). 

Does anybody know of a compiler that implements this? Or is this example
for future versions of Modula?

Michal Prussak

ugprussa@sunybcs.bitnet
ugprussa@cs.buffalo.edu
ugprussa@sunybcs.uucp