Re: beginning-of-defun (again)

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

  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.


>   though this can be slow, sometimes very slow.
> Setting it to non-nil makes it fast, but sometimes so inaccurate it
> looks like a bug.
>
>> A function resp. top-level-form starts if the beginning of a list is
>> followed by a respective keyword.
> Not necessarily: how does Emacs know whether something looking like a
> "top-level-form" is actually at the top level or not?

Top-level here is the beginning of a not nested list.
Remains to set the keywords more or less restrictive.

>    When
> open-paren-in-column-0-is-defun-start is non-nil, it need scan no
> further back than the first such paren encountered.  When
> o-p-i-c-0-i-d-s is nil, it must scan all the way from the beginning of
> the file.
>
>> The list of keywords being customizable seems a plus :)
> This would not work in all modes.
>

The default can't work in all modes but be reliable in Emacs Lisp.