Re: implementing a callback interface for a RecDescent parser

Many moons back, Dave McD wrote:

> I have built a parser which is working very well
> except for the line numbers being printed in error
> messages are negative numbers.  It looks like if you
> add the TOTAL line count for the $text to this, then
> you get the correct line # + 1.  Seems like a bug.
> Maybe I can get around it by initializing the starting
> line # with the total line count when I first call the
> parser as an extra argument?
> 
> Also, I looked at your implementation of the TIE'ed
> subroutine to the $thisline variable in RecDescent.pm,
> and its seems really inefficient to have to compute
> the line number by counting lines for the remaining
> $text at the parse point, and subtracting the total
> lines for the intial $text.  On long input files, if I
> use the $thisline variable in my grammer, it slows the
> parse down by like 5-10X.  Is there not some way to
> carry a running total of newlines seen as the parse
> proceeds, similar to how $text is localized per rule?

Almost certainly. I'm now building my next parser generator
(Parse::FastDescent) which I hope will be decidely more efficient
in this (and many other) respects.

Damian