Path: news.daimi.aau.dk!news.uni-c.dk!sunic!trane.uninett.no!nntp.uio.no!ifi.uio.no!nntp!alfh
From: alfh@byleist.ifi.uio.no (Alf-Ivar Holm)
Newsgroups: comp.lang.beta
Subject: Recursive, double INNER
Followup-To: comp.lang.beta
Date: 06 Feb 1995 19:42:01 GMT
Organization: Dept. of Informatics, University of Oslo, Norway
Lines: 73
Message-ID: <ALFH.95Feb6204201@byleist.ifi.uio.no>
NNTP-Posting-Host: byleist.ifi.uio.no
CC: 

This is a recursive function with two INNER clauses:

	forAllThings:
	(# 
	do
	   INNER;
	   ... &forAllThings ...
	   INNER;
	#);
		
The main problem here is that the user of the function has to know
about the double INNER and make some code to identify which INNER is
being processed.

I thought that I could overcome this by changing the two INNER parts
to two virtual functions, 'before' and 'after':
	
	forAllThings:
	(# 
	   before:< object;
	   after:< object;
	do
	   before;
	   ... &forAllThings ...
	   after;
	#);
		
It works, but there are one more problem, if you make a sub pattern,
e.g. forAllDingbats, the forAllThings super pattern is still called.

Next thought:  Make a virtual function, 'callMe', which is bound to
the current (sub)pattern:
	
	forAllThings:
	(# 
	   before:< object;
	   after:< object;
	   callMe:< forAllThings;
	do
	   before;
	   ... &callMe ...
	   after;
	#);

Now, I can make forAllDingbats and bind callMe to that sub pattern:
	
	forAllDingbats: forAllThings
	(# 
	   before::< (# ... #);
	   after::< (# ... #);
	   callMe::< forAllDingbats;
	#);

Finally, I would usually use forAllThings directly, not making a
specific sub pattern:
	
	do
           ...
           &forAllThings
	   (# 
	      before::< (# ... #);
	      after::< (# ... #);
	      callMe::< (* What am I supposed to put here? *) ;
	   #);
	     
My problem is that I don't manage to bind callMe to that specific
instance.  

What am I missing?  Some minor syntactic detail?  Some major
fundamental issues about programming or BETA?  A course about
rewriting recursive algorithms to non-recursive?

	Affi