Re: Appending lists

[Jean Louis]

* tomas@tuxteam.de <tomas@tuxteam.de> [2021-06-16 10:29]:
> On Wed, Jun 16, 2021 at 03:11:43AM +0200, Emanuel Berg via Users list for the 
> GNU Emacs text editor wrote:
> > tomas wrote:
> > 
> > > (setq thing (copy-sequence '(one two three four five six)))
> > > (setq thang (cddr thing))
> > >
> > > thang => (three four five six)
> > >
> > > (nreverse thing) => (six five four three two one)
> > >
> > > thing => (one)
> > >
> > > thang => (three two one)
> > >   ; now this is what I was after. Who the heck "changed my
> > >   ; variable!?" Who is General Failure and why is he reading
> > >   ; my disk?
> > 
> > Well, let's see, `nreverse' has updated the data without
> > setting the variables to whatever desired values they should
> > take
> 
> It can't. It's a function.
> 
> Doing (foo x y) will *never* change "the variable x" -- unless
> foo is a macro/special form.

(setq list-1 '(1 2 3))
(setq list-2 '(A B))
(nconc list-1 list-2) ⇒ (1 2 3 A B)
list-1 ⇒ (1 2 3 A B)
nconc is a built-in function in ‘C source code’.

So it obviously changes the variable `list-1' from (1 2 3) to (1 2 3 A
B) -- how do you explain that?

So far I know from Common Lisp those functions starting with "n" are
common with side effects.

(nreverse list-1) ⇒ (B A 3 2 1)
list-1 ⇒ (1) ⁈⁈⁈⁈⁈⁈⁈⁈⁈⁈⁈

-- 
Jean

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