Re: Google summer of code

[Derek M Jones]

Satya,

> I decided to go ahead and contribute independently. That way, even
> though I don't get paid, I will (hopefully) learn something. So if
> there isn't anyone contributing to the same project through google
> summer of code, please consider mentoring me. My aim is to gain a
> thorough knowledge of bison internals and practical issues in
> implementation of parsing algorithms.

For what it is worth I can offer some advice.  First it is great that
you want to work on a project like this over the summer and I hope
you find it worthwhile.

Understanding bison internals sufficiently well to modify them will
take longer than one summer.  While the algorithms look straight
forward there are lots of subtle interactions.

Producing one or more variants of the parser skeleton sounds
like it is possible in the amount of time available.

> Project title: Implementation of Burke-Fisher Error correction
> implementation for bison C output.

Syntax recovery from an error on the input stream is something of
a black art whose techniques never seem to get written down.  In
you simply write down what you learn over the summer you will have
contributed some useful material.

My experience with syntax error recovery (Pascal, CHILL, C, and SQL)
is that no one technique works for the common errors.  A combination
of, depending on context,  delete to some token or insert some token
needs to be performed.  I have always made the selection by running
common cases through a parser and trying different recover methods,
then coding up, for a given situation, the ones that work best.

The main requirement is to resync so that cascading syntax errors
are avoided.  One compiler I worked on did multiple parses, using
different combinations of error recovery, looking for the one that
parsed the largest amount of input (up to some limit) without
generating any other syntax errors.

--
Derek M. Jones                              tel: +44 (0) 1252 520 667
Knowledge Software Ltd                      mailto:address@hidden
Applications Standards Conformance Testing    http://www.knosof.co.uk