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 06:54]:

>   ;; Why do the rest of this?
>   ;; Search for a nil, after the non-nil car?
>   ;; Then copy the entire list.  Then delete
>   ;; all nils from it?  Why on earth do this?
>   (if (memq elt list)
>        ^^^^
>       (delq elt (copy-sequence list))
>                  ^^^^^^^^^^^^^
>        ^^^^^^^^^
>     list))

I get your reasoning. Maybe my function was not named correctly and
then your logic jumps in. 

> You certainly don't need to remove all nils
> from the list.  If your list is 100,000,000
> elements long and the first element is t, why
> would you want to copy the entire list and
> then remove all the nils from it?  Testing
> the first element tells you the answer.

I get the reasoning, you are right, though maybe not in the context of
testing if list has at least one non nil element. I am not sure, you
know is not easy to grasp all.

What I know is that by testing the first element does not tell the
answer if list has any non nil element:

(let ((my-list '(nil nil nil nil)))
    (car my-list)) ⇒ nil

(let ((my-list '(nil nil nil nil 1)))
    (car my-list)) ⇒ nil

So testing the first element did not give me the answer that
 my-list has one non-nil element.

Maybe you can show in Emacs Lisp practically how do you mean it.

-- 
Jean

Take action in Free Software Foundation campaigns:
https://www.fsf.org/campaigns

In support of Richard M. Stallman
https://stallmansupport.org/