On Mon, Dec 14, 2020 at 04:43:24PM -0700, William G Hatch wrote:
> On Wed, Dec 02, 2020 at 01:56:41PM -0500, Sam Tobin-Hochstadt wrote:
> > A few thoughts on these topics, which I've been thinking about for a while.
> >
> > First, let's distinguish two things. One is an _incremental_ system,
> > such as a parser, which is one which does less work in response to a
> > small change than it would need to do from scratch. The other is a
> > system with _error recovery_, which is one where in the presence of
> > one error, the system can still provide a useful answer and/or
> > continue on to discover other errors. tree-sitter, for example, aims
> > to do both of these, but they're quite different.
>
>
> I thought I might as well chime in here that I'm currently working on
> an incremental parsing system for Racket that will support parser
> combinators, BNF, and arbitrary ad-hoc parsing procedures. I already
> have a parsing system[1] that supports expressive parsing with any mix
> of those constructors that supports all context-free grammars and
> beyond, so that much is already “successful”. Unfortunately, I
> haven't been able to make it as performant as I would like. The
> original goal wasn't to support incremental parsing, and I didn't
> write incremental support into that implementation. However, while
> trying to optimize it I also decided to figure out how to make it
> incremental, so now I have the solution for that too.
>
> I'm now working on another similar parsing system that is a little
> less expressive (in particular it has more limited support for
> ambiguous grammars, and thus doesn't support the full class of
> context-free grammars, though it will still support useful things
> outside of CFG, such as non-CFG things that Racket and Scribble
> parsers do), but should be much faster (because it gets to avoid extra
> work supporting the possibility of ambiguity). I'm adding my solution
> to incremental parsing support to this version. If I can ever make
> the original algorithm faster I'll add incremental support to it too.
> Both systems leverage delimited continuations at their core -- it
> turns out they are really useful for parsing, both for improving
> expressiveness and for incrementality.
>
> That said, I'm not currently aiming to solve the error recovery part
> of the problem.
Error recovery on reparsing?? Just use the parse you had from the
last good parse, but mark the parse tree where it doesn't match
the parsed string.
-- hendrik
>
> [1] https://github.com/willghatch/racket-chido-parse
>
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