Re: A faster derived-mode-p

[Lars Ingebrigtsen <larsi@gnus.org>]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

> Here's my suggestion:
> Instead of trying to speed up those 10K predicates we're going to have
> to evaluate, we could try to take advantage of the fact that there
> should be a lot of redundancy there.
>
> So we could do something like:
>
>     (let ((cmds (make-hash-table :test #'equal)))
>       (mapatom (lambda (sym)
>                  (when (commandp sym)
>                    (push sym (gethash (command-predicate sym) cmds)))))
>       (let (active-cmds)
>         (maphash (lambda (pred syms)
>                    (when (funcall pred)
>                      (cl-callf nconc active-cmds syms)))
>                  cmds)
>         active-cmds))

Hm, right...  As Dmitry showed, my worries about the inefficiency of
derived-mode-p seem exaggerated, but if it turns out to be a problem (or
we have more complex predicates), then doing something like this seems
promising.

However, the vast, vast number of the predicates basically devolve to
this (on the happy path):

(or (derived-mode-p 'foo-mode)
    (memq 'foo-mode minor-modes)
    (memq 'foo-mode global-minor-modes))

The derived-mode-p is fast, `minor-modes' is typically less than four
elements, and the same with `global-minor-modes'.  I'm not sure that
it's likely that looping over the symbols and entering the predicates
into a hash table has much scope for improving the speed much -- it'll
already be quite speedy.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no