Re: [Pyparsing] Get Better Error Messages - Prevent Backtracking

[Paul M. <pt...@au...>]

I am sorting out what to release in the next version of pyparsing.  I will
definitely include ErrStop or something similar.  I would also like to get
an idea of any patterns of usage, to see if there is a natural place to
automatically include this feature, in an And say.  Or perhaps just
incorporate this logic into the And class's parseImpl method.  Or make
raiseErrorStop an attribute of And (or maybe just of ParserElement), so that
any class can report its error location.

I'm also looking at something like lastParseLoc.  Ideally I'd like
lastParseLoc to be an attribute of a ParseStatus object that is passed
through the grammar - this would be a natural home for lastParseLoc, as well
as things like global debugging flags, whitespace character sets, packrat
caches, etc.  But I think I would also want to pass this object to parse
actions, and this would break the interface to all existing parse actions.
:(  So for now, it will probably have to be a class attribute, the same way
that the packrat cache is handled.

So these changes could get pretty drastic.  I'll keep them to a minimum for
compatability with 1.4.x, maybe bump the minor version to 1.5, and save the
really drastic changes for 2.0 someday.

-- Paul


-----Original Message-----
From: pyp...@li...
[mailto:pyp...@li...] On Behalf Of W.
Martin Borgert
Sent: Sunday, April 20, 2008 3:50 AM
To: Eike Welk
Cc: pyp...@li...
Subject: Re: [Pyparsing] Get Better Error Messages - Prevent Backtracking

On Mon, Apr 14, 2008 at 01:16:35AM +0200, Eike Welk wrote:
> I want to propose an other way, how to get better error messages: 
> Prevent backtracking at certain points in the grammar.

I like your approach and will probably use it in one of my two pyparsing
projects. Unfortunately, my other projects has about 600 BNF productions,
some of them non-trivial. Adding ErrStop to at least 100 or 200 of them
would clutter my code a lot and I'm yet sure it even would give the desired
result. For that grammar I still hope for inclusion of LastParseLoc or sth.
similar in pyparsing :~)

Thanks Eike, Gre7g, and Paul!


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