Re: [External] : Re: Testing whether a list contains at least one non-nil element

[Jean Louis]

* Drew Adams <drew.adams@oracle.com> [2022-10-27 18:54]:
> In the worst case for your code, the first element IS non-nil and
> you spend forever doing useless stuff.  In no case is your code as
> efficient as just testing each list element, starting at the
> beginning, and STOPPING as soon as you find a non-nil element.

Of course I agree with the thought in general.

Is it this below?

(defun check-if-any-elt-is-non-nil (list)
  (let (there-is)
    (while (and list (not there-is))
      (when (car list) (setq there-is t))
      (setq list (cdr list)))
    there-is))

(check-if-any-elt-is-non-nil '(nil nil nil nil nil nil nil nil 1 nil)) ⇒ t

(check-if-any-elt-is-non-nil '(nil nil nil nil nil nil nil nil nil)) ⇒ nil

(benchmark 10000000 (check-if-any-elt-is-non-nil (append (list 1) (make-list 
1000000 nil)))) ⇒ "Elapsed time: 0.771948s"

(benchmark 10000000 (check-if-any-elt-is-non-nil (append (make-list 1000000 
nil) (list 1) ))) ⇒ "Elapsed time: 0.744323s"

-- 
Jean

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