Re: Idea for syntax-ppss. Is it new? Could it be any good?

[Lennart Borgman (gmail)]

Alan Mackenzie wrote:
> Hi, Emacs,
>
> Looking at the doc string for syntax-ppss, it seems this could be _very_
> useful in a certain body of code I'm responsible for.  That body of code
> has a lot of heuristics that determine whether point is within a
> string/comment, and some of these are not watertight (such as hard-coded
> limits on comment sizes to achieve speed).  Basically, they're a PITA.
> syntax-ppss, if it was guaranteed watertight, could remove the gnawing
> uncertainty from much of the code.
>
> However, the manual documents limitations on syntax-ppss's functionality.
>
> How about reimplementing it thusly?:  The current syntax would be cached
> for positions at every N bytes (where N would be, perhaps 1024, possibly
> 8192).  A call to syntax-ppss would simply call parse-partial-sexp from
> the latest valid cached position, filling out the cache as it goes.  Any
> buffer change would invalidate cached values for N > POS.

There are some defadvices for syntax-ppss and cousins in mumamo.el that 
does something like this. This is needed in multi major mode buffers if 
the normal font lock routines is used there.

I do not exactly do what you propose and a bit more is needed (for 
mumamo). I think however that any solution should take the need for 
multi major modes into account.

> I envisage coding this in C rather than Lisp.  There would be some
> complications to do with making sure the syntax table isn't tampered
> with, and so on.  This code would surely be fast and reliable.
>
> Obviously I'm not proposing this for the pending release, but what do
> people think about the idea?