Re: [External] : Passing buffers to function in elisp

[<tomas@tuxteam.de>]

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On Tue, Mar 07, 2023 at 05:45:49PM -0500, Stefan Monnier wrote:
> >> This is a typical a source of unnecessary O(N²) complexity: the above
> >> line takes O(N) time, so if you do it O(N) times, you got your
> >> N² blowup.  You're usually better off doing
> >>
> >>     (push (plist-get page :stream) stream-chunks)
> >>
> >> and then at the end get the `stream` with
> >>
> >>     (mapconcat #'identity (nreverse stream-chunks) nil)
> >> or
> >>     (apply #'vconcat (nreverse stream-chunks))
> >
> > Right, I see.  Stream chunks are in this case byte vectors, so
> > just reversing those chunks does not do the trick.
> > But surely I can get from an order of N² to 2N or so.
> 
> I'm suggesting to build a list of chunks backward and to reverse *the
> list*, not the chunks.  So the end result should still be the same.

Judging by the "2N instead of N^2" I guess Petteri had the right
mental model, though.

> > Okay, this is something I did not foresee.  But what about eval-defun
> > and eval-... in general?  They are very convenient when trying out
> > things.
> 
> It's OK to use them, of course.  It usually means you still have 98% of
> your code compiled.
> 
> >> The compiler is your friend.  He can help you get the code in good
> >> shape :-)
> > I'm afraid that even the compiler cannot help against quadratic
> > complexity blunders.
> 
> :-)
> 
> It's just a friend, yes.

:-)

Cheers
-- 
t

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