[developers] Stack overflow in generator unpack-edge

[Dan Flickinger]

Thanks, Berthold, for that very good suggestion to run the generator on my problematic example with packing turned off.  I could then immediately see that I had recently introduced a bug into the lexical entry for the complementizer `for', which led to serious overgeneration.  Now that I have fixed the bug, the example generates fine, both without and with packing.  

Thus it seems that at least in some cases, the generator with packing on will produce a "Stack overflow" message on an item where generating without packing produces the more informative usual warning about a possibly recursive rule, which is then immediately visible in the generator chart.   So perhaps there is no need to change anything in the generator -- sensible grammar developers will of course remember to examine problematic generation examples with packing disabled.

Sorry for the false alarm, developers.

 Dan


----- Original Message -----
From: "Berthold Crysmann" <crysmann at ifk.uni-bonn.de>
To: "Dan Flickinger" <danf at stanford.edu>
Cc: "developers" <developers at delph-in.net>
Sent: Friday, January 15, 2010 1:26:56 PM GMT +01:00 Amsterdam / Berlin / Bern / Rome / Stockholm / Vienna
Subject: Re: [developers] Stack overflow in generator unpack-edge

On Thu, 2010-01-14 at 23:38 -0800, Dan Flickinger wrote:
> Using the current SVN versions of the ERG and the LKB, I get a stack overflow error resulting from a tight self-calling loop in the generator's unpack-edge!!() when generating (with packing) from the expletive-it subject (NP-X) reading of the sentence 
>   It fails to rain.
> It seems that the generator may be having difficulty distinguishing the edge "to rain" from the edge "for it to rain", both of which have identical semantics.
> 
>   Dan
Hi Dan, 

I occasionally bump into this with semantically vacuopus triggered
items.  What happens if you switch  packing off? Does "it" (or "for it")
combine more than once? 

Berthold