Re: PL support (was: Drop the Copyright Assignment requirement for Emacs)

[Eli Zaretskii <eliz@gnu.org>]

> From: Daniel Colascione <dancol@dancol.org>
> CC: <emacs-devel@gnu.org>, <monnier@iro.umontreal.ca>, <dgutov@yandex.ru>
> Date: Sat, 09 May 2020 08:50:45 -0700
> 
> > Please someone start working on this ASAP.  We sorely need that, just
> > look at the recent discussions on Reddit that underline these
> > deficiencies in Emacs.
> 
> It's a hard problem. A mode based on a real parser must be fast, 
> incremental, and robust against transient errors that arise in the normal 
> course of editing.

I agree.  But other IDE's have the same problem, don't they?  And
AFAIU incremental parsers such as tree-sitter are explicitly targeting
such use patterns, and their documentation says they are tolerant to
temporarily incorrect source.

> We'd also want the ability to parse complex languages 
> (far beyond LALR) and incorporate out-of-band information in order to 
> resolve semantic ambiguities --- e.g. the C++ template problem. On top of 
> all that, the parser would need to be highly malleable to make it easy to 
> adjust to slight differences in dialect as well as deal with multiple 
> languages in a buffer.

AFAICT, tree-sitter supports many languages already.  I know less
about LSP, but I'm guessing they are not very far of that, either.

> A much simpler approach I've also had in mind is providing a C-assisted 
> incremental parser combinators facility to Lisp --- something like the 
> venerable pyparsing. Parser combinators make it pretty easy to incorporate 
> error recovery rules, and the C code can use approaches like current 
> syntax-ppss to keep the parse up to date and maintain, cheaply, an AST.

I'm sure more than one alternative exist, and maybe we should support
more than one.

Thanks.