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From: mareb@lux.sait.edu.au (Buckley)
Newsgroups: comp.compilers
Subject: Re: Avoiding right-recursion
Keywords: yacc, parse
Message-ID: <9101290649.AA11150@lux.sait.edu.au>
Date: 29 Jan 91 16:19:41 GMT
References: <MIKE.91Jan23103603@client25.prg.ox.ac.uk>
Sender: compilers-sender@iecc.cambridge.ma.us
Reply-To: mareb@lux.sait.edu.au (Buckley)
Organization: Compilers Central
Lines: 28
Approved: compilers@iecc.cambridge.ma.us

>From: Mike.Spivey@prg.oxford.ac.uk (Mike Spivey)
>A better approach in some ways is to use left recursion but do extra
>work to build the list:

I like to use a cyclically linked list - the tail of the list points
back to the head. The list pointer points to the tail (or nil for
an empty list). It is very easy to append to this list and when you are
done it is very easy to convert it to a conventional list. And you still
only need one pointer.

I guess this would look something like this:

	list	: CLlist	{ $$ = tail($1); tail($1) = nil; } ;
	CLlist	: item		{ $$ = tail($1) = $1; }
		| CLlist ',' item { tail($3) = tail($1); $$ = tail($1) = $3; }
		;


	b++
__
Bob Buckley                                  Phone: (08) 343 3465
School of Mathematics & Computer Studies     Fax:   (08) 349 4367
University of South Australia
The Levels SA 5095                         email: mareb@lux.sait.edu.au
Australia
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