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From: alfh@byleist.ifi.uio.no (Alf-Ivar Holm)
Newsgroups: comp.lang.beta
Subject: Re: Recursive, double INNER
Date: 10 Feb 1995 14:33:20 GMT
Organization: Dept. of Informatics, University of Oslo, Norway
Lines: 40
Message-ID: <ALFH.95Feb10153320@byleist.ifi.uio.no>
References: <ALFH.95Feb6204201@byleist.ifi.uio.no> <3hdl0d$c2l@belfort.daimi.aau.dk>
NNTP-Posting-Host: byleist.ifi.uio.no
In-reply-to: jco@daimi.aau.dk's message of 9 Feb 1995 17:56:29 GMT
CC: 

In article <3hdl0d$c2l@belfort.daimi.aau.dk> jco@daimi.aau.dk (Jens Cornelius Olsen) writes:

> My solution would be to use THIS() and pattern variables.  In a *true*
> recursive version this amounts to something like this
> 
>    forAllThings:
>      (#
>         before:< object;
>         after:< object;
>         callMe: ##forAllThings;
>      do before;
>         this(forAllThings)##-> callMe##; &callMe;
>         after;
>      #);

Wow, it's so obvious now :-)  

This version is also much nicer than the one with a virtual "callMe"
in the sense that the sub patterns only need to worry about "before"
and "after", no fuzz with "callMe" (further binding).

This is also a nice application of the pattern variable.

> Where the pattern variable is used to duplicate the subpattern of forAllThings
> in question.  From previous email correspondance with Ole Lehrmann Madsen, one
> of the designers of BETA, I know that it was (or is) considered to include
> a shorter version of the two statements involving callMe in the syntax:
> 
>                  &(this(forAllThings)##)
> 
> but for now we are forced to use the callMe variable.

Although the 

	(this(patternName)##)

statement would be shorter, I guess the use would be limited to object
creation. (No computed references and the like.)

	Affi