[lojban] Re: PEG left recursive definitions

["Jorge Llambías" <lojban-out@lojban.org>]

On 10/31/07, Chris Capel <pdf23ds@gmail.com> wrote:
>
> Do you not think that the grammar definition itself would be better
> expressed with explicit left-recursion?

Yes, I do, for the cases of left associativity. So for example the
left recursive:

   sumti-2 <- (sumti-2 joik-ek)? sumti-3

would reflect the left associativity better than the current:

   sumti-2 <- sumti-3 (joik-ek sumti-3)*


> >   expr <- expr '?' expr ':' expr / 'x'
> > which would not be allowed in PEG.
>
> Well, "not allowed" in most implementations of PEG. (Although direct
> left recursion *is* rewritten automatically in Pappy.) But since it's
> isomorphic (i.e. identical after rewriting) to a non-left-recursive
> definition, I don't see why you'd say it's not allowed at all.

I probably used the wrong words. I don't know much more about
this than what I learned from the Lojban PEG. I meant it would not be
allowed in Robin's implementation.

mu'o mi'e xorxes


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