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Re: LAC (lookahead correction) for syntax error handling

From: Joel E. Denny
Subject: Re: LAC (lookahead correction) for syntax error handling
Date: Sat, 29 Jan 2011 11:08:49 -0500 (EST)
User-agent: Alpine 2.00 (DEB 1167 2008-08-23)

On Wed, 26 Jan 2011, Akim Demaille wrote:

> > Perhaps most notably, LAC fixes the expected token list in syntax 
> > error messages produced by %error-verbose.  See NEWS for more details.
> This is nice work.  I have not read it in all the details, but it is, as 
> usual, well commented, documented, and tested.

By the way, thanks!

Of course, if you (or anyone) have a chance to try out LAC in your own 
projects, I'd be interested in hearing of your experiences with it.  Keep 
in mind that's it's useful for LALR, IELR, and canonical LR.

Also, there is another problem with syntax error messages that we've 
discussed before and that LAC might expose further.  Sometimes, when it 
seems LAC should correct the expected token list in a syntax error 
message, both the unexpected token and the expected token list are simply 
dropped.  The problem here is that, for the sake of translation, the 
expected token list is limited to 4 tokens.  I'm thinking the user ought 
to be able to control the limit, possibly removing the limit entirely. 
Surely we can find some way to handle the translation issues.

In any case, unless there's a simple fix, I don't expect to address this 
in 2.5, but I should probably document it.  NEWS should probably at least 
mention that there are some minor caveats to read about in the manual.

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