Re: How detect cycle in grammar ?

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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