[lojban] PEG grammar issues

["Chris Capel" <pdf23ds@gmail.com>]

I've found a few minor issues with the PEG grammar over the course of
working on it, and I thought I'd start to tell people about them in
case I forget them.

First, the top-level production should fail if it can't parse the
whole string. Currently 'text' ends with an EOF?, which makes it never
fail. However, it can't be EOF, because LU references the text
production, and doesn't require an EOF before "li'u". 'text' should be
changed to something like

text-eof <- text EOF

text <- intro-null NAI-clause* text-part-2 (!text-1 joik-jek)? text-1?
faho-clause

I made this change in my parser in the first release, and it seems to work fine.

Second, selbri-3 should parse its child selbri-4 into left-associative
groups. Currently it just parses them all into one group, which is
misleading and possibly wrong, depending on your interpretation. I
tried to figure out a way to fix this, but couldn't find a way to do
so and avoid left recursion in the definition. So I gave up and added
a post-parsing step in my own parser to group them properly.

Third, tenses that probably ought to be parsed as part of the bridi
are currently being parsed as head terms, because of the term-1
production:

   term-1 <- sumti / ( !gek (tag / FA-clause free*) (sumti /
KU-clause? free*) ) / termset / NA-clause KU-clause free*

   {mi} {pu} <klama le zarci>

(In braces are term-1 matches, and in angle brackets is the
bridi-tail.) 'term-1' matches "mi", and then it matches "pu". 'sumti'
fails on "pu", but '!gek' and 'tag' succeed, and then since
'KU-clause' and 'free' are both optional, the second option of
'term-1' succeeds. I'm not exactly sure how this one needs to be
fixed, but what about this:

   term-1 <- sumti / term-2 / termset / NA-clause KU-clause free*

   term-2 <- !gek (tag (sumti / KU-clause free*) / FA-clause free*
(sumti / KU-clause? free*) )

Here, 'term-2' is the second option of the original 'term-1', except
that the third item in the sequence has been factored into the second,
and the ? removed from 'KU-clause' after 'tag'. It seems to work in my
parser!

Fourth, 'term-sa' only appears to match one term sa under some
conditions. For instance, it doesn't match this:

   mi ba klama lo sa lo sa do

which one might imagine could be said by someone with a stutter.
Here's one possible fix:

   term-sa <- term-start (!term-1 (sa-word / SA-clause !term-1) )*
SA-clause &term-1

Well, that's about it for now. Number 3 is currently a problem for my
parser, as it makes it hard for me to correctly gloss tense cmavo in
context. So if anyone sees a problem with my correction, let me know.

Chris Capel
-- 
"What is it like to be a bat? What is it like to bat a bee? What is it
like to be a bee being batted? What is it like to be a batted bee?"
-- The Mind's I (Hofstadter, Dennet)


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