Re: `looking-back' strange warning

[Tassilo Horn <tsdh@gnu.org>]

Drew Adams <drew.adams@oracle.com> writes:

>> This version is about 6 times faster in the t case and a still a bit
>> faster in the nil case where the char before point is already different
>> (which is the best case for your function).
>> 
>> (defun chars-before (chars)
>>   "Return non-nil if the literal string CHARS is right before point.
>> This is more efficient that `looking-back' for this use case."
>>   (let ((beg (- (point) (length chars))))
>>     (unless (< beg 0)
>>       (save-excursion
>> 	  (goto-char beg)
>> 	  (looking-at (regexp-quote chars))))))
>
> OK.  Good to know.
>
> See also bug #17284,
> http://debbugs.gnu.org/cgi/bugreport.cgi?bug=17284,
> where this has been discussed and I and others proposed
> code for this.

Martin's version is faster than mine, so no need to propose it.

> You are welcome to contribute to that (short) bug thread,
> or to otherwise try to get such a function added to Emacs.

I think that function is not really a viable drop-in replacement for
typical `looking-back' calls.  The latter is most frequently used to
decide "am I behind some word or sequence of words, and I don't care
about whitespace?".

Bye,
Tassilo