[lojban] Re: gleki xisri'i

[Robin Lee Powell <rlpowell@digitalkingdom.org>]

On Thu, Dec 25, 2008 at 07:41:52PM +0000, Minimiscience wrote:
> > It looks like a yacc-specific trick.
> 
> I wouldn't call it a "trick"; it's a documented & well-known
> feature.  Besides, so what if it's Yacc-specific?  

We asked for a general CFG, not something that only works in some
specific grammar generator.

> So, I guess I have two questions: what makes you think that %prec
> makes the grammar non-context-free, 

Because there is no formal definition of it, for one thing.  It's
not nearly as obvious as you seem to think; there have been serious
papers written on the topic:

http://shrunklink.com/bkop

Furthermore, and this is much more important, unless I'm really
missing something you're *changing the precedence as the grammar is
parsed*.  That is, if a parse doesn't work without a particular
terminator you drop the precedence of that terminator-free
production to zero *at parse time*.  If that's reducable to a
4-tuple a la http://en.wikipedia.org/wiki/Context_free_grammar I'd
be *really* surprised indeed!

> and if you were to somehow get a working context-sensitive grammar
> for a parser generator that is only expected to work for CFGs,
> what would be the problem, 

We already have one; that's exactly what the official parser is.
The only difference is that you use %prec to modify precedence
during parsing, whereas the current official parser uses the error
production to do the same thing.

Such a thing cannot be formally reasoned about, and (much more
importantly) is hard to port to other parser generators.  A pure CFG
should be trivially portable to (picking one at random here) say,
ANTLR, but that's not true with %prec, since every grammar generator
that has such a thing, if it does, will do it differently.

> other than being kept from showing that Lojban grammar is
> context-free, which seems to be nothing more than a personal goal
> of yours?

Well, that was the point of the contest, so it matters in as much as
you seemed to be asking John and I to judge this as an entry to the
contest.  I'm afraid I have to say that it fails.  John may
disagree, but I doubt it.

-Robin

-- 
They say:  "The first AIs will be built by the military as weapons."
And I'm thinking:  "Does it even occur to you to try for something
other than the default outcome?" -- http://shorl.com/tydruhedufogre
http://www.digitalkingdom.org/~rlpowell/ *** http://www.lojban.org/


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