Re: [lojban] Lojban CFG Questions

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

On Fri, Dec 10, 2010 at 10:24:39AM +0100, Roman Naumann wrote:
> Hello dear lojbanistanians,
> 
> i'm starting with an attempt to find a CFG for lojban - or if it
> shows impossible, to prove it being impossible (so that you see
> what exactly is impossible and thus to improve).
> 
> Back in 2008 when there was a challenge [1] to do exactly that, i
> would have done it, but i lacked the knowledge to proof or
> proof-wrong grammars. Learned it during the last year at
> university and thought, hey, why not put it to use.

FWIW, formal proof is not required for the "yes we can" case; an
example grammar that clearly parses the language decently well will
do fine.

> However, i realized just now looking at the EBFN [2] causes eye cancer. 

Hahahah.

> Also, i've never been good with lojban at all. I don't get the
> (formalizing) problem with elidable terminators yet. To get
> started, it would be extremely helpful to work on an abstraction.
> I'd be glad if you could provide such to me.

Here's a very very simplified Lojban for you.  It has exactly 4
words: lenu, mi, klama, ku

(note to oldbies: yes, I treated lenu as one word; yes, those of you
who know me know I hate compound cmavo; it's a special case, go
stick your head in a pig)

A sentence is zero or more sumti, followed by klama, followed by
zero or more sumti.

A sumti is either "mi" or "lenu" followed by a sentence.

"ku" ends a "lenu" sentence immediately.

From what we have so far, you'd expect:
  
  lenu mi klama mi klama mi

to fail to parse, but in fact it parses just fine: because a
sentence can have only one "klama", upon seeing a second one the
parser goes "Oh, they forgot to put a "ku" in, but there needs to
be one for the parse to work, so I'll just insert it".  So what the
parser sees is actually:

  lenu mi klama mi ku klama mi

(note: not actually true in real Lojban)

Which, loosely, parses like so:

  sentence=( sumti=(lenu sentence=(mi klama mi) ku) klama mi)

That, in a nutshell, is the elidable terminator problem: making
terminators act as though they were included when they actually
weren't, but the sentence parses if they were (and doesn't if they
weren't).

You have to solve it *without* significantly changing the definition
of "sentence" I gave you.

Solving this toy version won't prove much about the full version,
but it's a good start.

-Robin

-- 
http://singinst.org/ :  Our last, best hope for a fantastic future.
Lojban (http://www.lojban.org/): The language in which "this parrot
is dead" is "ti poi spitaki cu morsi", but "this sentence is false"
is "na nei".   My personal page: http://www.digitalkingdom.org/rlp/

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