Re: [External] : Re: Appending lists

[Jean Louis]

* Emanuel Berg via Users list for the GNU Emacs text editor 
<help-gnu-emacs@gnu.org> [2021-06-20 23:50]:
> (setq list-head '(1)) ; (1)
> 
> (setq list-tail '(2 3 4)) ; (2 3 4)
> 
> (setq whole-list (append list-head list-tail)) ; (1 2 3 4)
> 
> (setcdr list-tail '(3.5 4)) ; (3.5 4)
> 
> whole-list ; (1 2 3.5 4) <-- the tail has changed
> 
> (setcar list-head 1.5)
> 
> whole-list ; <-- but here, the head is still unaffected, (1 2 3.5 4)
> 
> (setcar whole-list 1.33) ; well, of course that will work...
> 
> whole-list ; (1.33 2 3.5 4)
> 
> list-head ; still (1.5)

(setq list-head '(1)) ⇒ (1)

(setq list-tail '(2 3 4)) ⇒ (2 3 4)

(setq whole-list (append list-head (copy-sequence list-tail))) ⇒ (1 2 3 4)

(setcdr list-tail '(3.5 4)) ⇒ (3.5 4) ; (3.5 4)

It did not change now:
whole-list ⇒ (1 2 3 4) ; (1 2 3.5 4) <-- the tail has changed

(setcar list-head 1.5) ⇒ 1.5

whole-list ⇒ (1 2 3 4) ; <-- but here, the head is still unaffected, (1 2 3.5 4)

(setcar whole-list 1.33) ⇒ 1.33 ; well, of course that will work...

Look:
whole-list ⇒ (1.33 2 3 4) ; (1.33 2 3.5 4)

list-head ⇒ (1.5) ; still (1.5)

-- 
Jean

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

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