Re: beginning-of-defun (again)

["Andreas Röhler" <andreas.roehler@online.de>]

  On 29.10.2015 14:31, David Kastrup wrote:
> Andreas Röhler<andreas.roehler@online.de>  writes:
>
>>   On 29.10.2015 13:46, Alan Mackenzie wrote:
>>> Hello, Andreas.
>>>
>>> On Thu, Oct 29, 2015 at 12:24:48PM +0100, Andreas Röhler wrote:
>>>>     Hi guys,
>>>> maybe it's time to have a reasonable default-behavior of
>>>> beginning-of-defun in Emacs Lisp.
>>>> IMO there is no reason for stuff like
>>>> open-paren-in-column-0-is-defun-start
>>> Unfortunately, there is.  Setting it to nil ensures accurate recognition
>>> of non-nested parens,
>> Sorry, Alan, but if there is no syntax expecting a start in column 0,
>> there is no reason to assume that.
>>
>> Relying on such means working in some cases, in other not. You won't
>> want that.
> If Emacs becomes too slow for useful work otherwise, that's no
> alternative to it sometimes making assumptions leading to bad
> highlighting.
>

Where it was proven Emacs is slow WRT an reasonable implementation, if 
such a thing doesn't exist?
AFAIK the current buggy one predates parse-partial-sexp and that part 
was never reconsidered WRT pps since.

Slow is the current "re-search-backward (if defun-prompt-regexp" stuff, 
which might be replaced by calls to pps + keyword.