Re: Musings: Supposed places of safety, guaranteed by parse-partial-sexp are not safe.

[Alan Mackenzie <acm@muc.de>]

Hello, Martin.

On Tue, Dec 06, 2011 at 11:15:22AM +0100, martin rudalics wrote:
>  > The parse-partial scanner works strictly left to right.  If (nth 5
>  > ppss) records the left hand bit of "/*", we are not yet in a
>  > comment.  We're probably about to do a division.  Similarly, after *
>  > of "*/", we're still in the comment, probably just passed a comment
>  > prefix.

> If we can look ahead by one character, there is no probability but
> certainty.  And the latter is what you want in (nth 4 ppss).  The
> remaining case is with an "/" at the end of a buffer and that case
> wouldn't trouble me.

One can delete anything inside a comment and it is still a comment.  We
(i.e. I :-) don't want to introduce an extra special case about the first
character of a comment.

>  > I disagree.  I think keeping the stricly L to R invariant of the
>  > parse is critically important (but don't ask me why :-).

> Why would looking ahead violate a L to R rule?

Think of it as the direction one's head is turned on a British street
when about to cross it suicidally.  At the moment, parse-partial-sexp
looks only at the characters to the left; it never pays any attention
whatsoever to characters on the right.

p-p-s is a finite state machine.  If it starts looking to the right, it
will still be a fsm, but with many more states.

Again, what of "/*/" mentioned by Stefan?  If we're already in the
comment after the first "/", then we're apparently looking at a comment
ender.  This complication (and it is complicated) surely condemns the
approach.

I think we should use the same approach as for escape characters: record
the fact in (nth 5 state) that we've passed one, but otherwise take no
action.

> martin

-- 
Alan Mackenzie (Nuremberg, Germany).