Re: How detect cycle in grammar ?

Path	csiph.com!x330-a1.tempe.blueboxinc.net!newsfeed.hal-mli.net!feeder3.hal-mli.net!newsfeed.hal-mli.net!feeder1.hal-mli.net!nx01.iad01.newshosting.com!newshosting.com!novia!border4.nntp.dca.giganews.com!border2.nntp.dca.giganews.com!nntp.giganews.com!news.iecc.com!nerds-end
From	anton@mips.complang.tuwien.ac.at (Anton Ertl)
Newsgroups	comp.compilers
Subject	Re: How detect cycle in grammar ?
Date	Mon, 28 Nov 2011 16:46:51 GMT
Organization	Institut fuer Computersprachen, Technische Universitaet Wien
Lines	23
Sender	news@iecc.com
Approved	comp.compilers@iecc.com
Message-ID	<11-11-066@comp.compilers> (permalink)
References	<11-11-041@comp.compilers> <11-11-045@comp.compilers> <11-11-050@comp.compilers> <11-11-057@comp.compilers>
NNTP-Posting-Host	news.iecc.com
X-Trace	leila.iecc.com 1322549622 65715 64.57.183.58 (29 Nov 2011 06:53:42 GMT)
X-Complaints-To	abuse@iecc.com
NNTP-Posting-Date	Tue, 29 Nov 2011 06:53:42 +0000 (UTC)
Keywords	parse, theory
Posted-Date	29 Nov 2011 01:53:42 EST
X-submission-address	compilers@iecc.com
X-moderator-address	compilers-request@iecc.com
X-FAQ-and-archives	http://compilers.iecc.com
Xref	x330-a1.tempe.blueboxinc.net comp.compilers:368

Show key headers only | View raw

Gene <gene.ressler@gmail.com> writes:
>It's also worth noting that any grammar with A->A in it is ambiguous
>in a way that should cause LR table generation to fail.  How would a
>parser know how many times to reduce A->A?

S -> A|B
A -> A
B -> t

This grammar can derive only the word "t", and only in one way.  I see
no ambiguity; no word can be derived in two ways in this grammar.

As for warning about these useless cycles, sure, they may indicate a
programming mistake, so better warn about them.  I still don't see
that they are a problem as far as their meaning is concerned, nor
wrt. implementability in general.  Apparently the Bison implementors
thought so, too, or Bison would produce an error, not a warning.

- anton
--
M. Anton Ertl
anton@mips.complang.tuwien.ac.at
http://www.complang.tuwien.ac.at/anton/

Back to comp.compilers | Previous | Next — Previous in thread | Next in thread | Find similar

Thread

How detect cycle in grammar ? Borneq <a.moderacja@gmail.com> - 2011-11-20 08:48 -0800
  Re: How detect cycle in grammar ? Hans Aberg <haberg-news@telia.com> - 2011-11-21 18:14 +0100
  Re: How detect cycle in grammar ? Gene <gene.ressler@gmail.com> - 2011-11-21 10:20 -0800
    Re: How detect cycle in grammar ? anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2011-11-22 15:20 +0000
      Re: How detect cycle in grammar ? Quinn Tyler Jackson <quinn_jackson2004@yahoo.ca> - 2011-11-25 22:28 -0800
      Re: How detect cycle in grammar ? Gene <gene.ressler@gmail.com> - 2011-11-27 10:18 -0800
    Re: How detect cycle in grammar ? Borneq <a.moderacja@gmail.com> - 2011-11-23 12:56 -0800
    Re: How detect cycle in grammar ? Borneq <a.moderacja@gmail.com> - 2011-11-24 09:24 -0800
      Re: How detect cycle in grammar ? Gene <gene.ressler@gmail.com> - 2011-11-27 10:27 -0800
        Re: How detect cycle in grammar ? anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2011-11-28 16:46 +0000
          Re: How detect cycle in grammar ? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2011-11-29 07:31 +0000
            Re: How detect cycle in grammar ? Paul B Mann <paul@paulbmann.com> - 2011-12-01 02:46 -0800
              Re: How detect cycle in grammar ? Quinn Tyler Jackson <quinn_jackson2004@yahoo.ca> - 2011-12-02 09:20 -0800
          Re: How detect cycle in grammar ? Gene <gene.ressler@gmail.com> - 2011-12-07 06:29 -0800

csiph-web