Re: [SimpleParse] Graceful failure ?

[H. T. H. <hi...@co...>]

On Thu, Mar 18, 2004 at 06:08:01PM -0500, Mike C. Fletcher wrote:
> H. T. Hind wrote:
> 
> >Hello, 
> >
> >Is there a way to get Simpleparse to gracefully exit instead
> >of going into an infinite loop ? 
> >
> >For example if I have a grammar definition like this 
> >
> >column_specs := '<s>',ws,('<c>',ws)+,'\n'
> >
> >then the system would go into an infinite loop if the input
> >contains '<S>' '<c>' 
> > 
> >
> I don't see how it could with the given definition.  Infinite loops 
> occur when you have a grammar like this:
> 
> column_specs := '<s>',ws,('<c>'?,ws)+,'\n'
> 
> that is, where you have a group that can match entirely with a null 
> group and then you add an outer repeating modifier.  As defined, the 
> engine allows for external parsers and the like which may, in fact, have 
> a null-length match, so to catch this, would need to extend how 
> mxTextTools communicates success/failure to allow for another state.
 
Is there another way to define the above that avoids the loop ?
We might not be able to anticipate all the data that we might
encounter, hence it is essential to have the ability to fail with
an error such that a human can intervene and fix the data. 

> It's possible to catch it, yes, but it would require some considerable 
> work to modify the engine to be able to support the feature.
> 

Would you recommend then something like PLY ?

Regards,
hth