Re: Problems with syntax-ppss

[Lennart Borgman (gmail)]

Alan Mackenzie wrote:
> Hi, Emacs!
>
> I've just encountered a rather knotty problem in CC Mode for which
> syntax-ppss ought to be a solution; I need to find out, RAPIDLY, whether
> a particular buffer position is inside a string or comment.
> Unfortunately (for me), ......
>
> syntax-ppss does it's parsing from (point-min), not from BOB.
>
> So if the buffer is currently narrowed, this function will return an
> meaningless value for the envisaged use.
>
> But if I widen the buffer first, what happens to syntax-ppss's cache?
> Is this just discarded, or are perhaps two caches maintained (one from
> BOB, the other from the current (or most recent) (point-min)?

I believe nothing happens to the cache. The cache is just a list of 
position + state. There is no reason to change this when widening the 
buffer.

The cache is flushed in before-change-hook. All entries after first 
changed position are removed.

> Advice, please!
>
> Forgive me at this point for not reading the fine source code - it's
> over 150 lines and looks rather forbidding.
>
> It would be nice if the the Elisp manual could be more explicit on such
> points.  (Hey, tell me how it is, and I'll expand the manual!)
>
> I think the doc-string for the function is inadequate - it fails to
> state that parsing starts at (point-min) rather than BOB.
>
> Thanks in advance!