Re: How detect cycle in grammar ?

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From	Gene <gene.ressler@gmail.com>
Newsgroups	comp.compilers
Subject	Re: How detect cycle in grammar ?
Date	Wed, 7 Dec 2011 06:29:33 -0800 (PST)
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On Nov 28, 11:46 am, an...@mips.complang.tuwien.ac.at (Anton Ertl)
wrote:
> Gene <gene.ress...@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.

We are really down in the weeds. I should have said any reduced
grammar (with useless non-terminals already removed).

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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

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