Re: Appending lists

[tomas]

On Wed, Jun 16, 2021 at 09:24:19PM +0000, Philip Kaludercic wrote:
> <tomas@tuxteam.de> writes:
> 
> > On Wed, Jun 16, 2021 at 08:36:00PM +0300, Jean Louis wrote:
> >> * Philip Kaludercic <philipk@posteo.net> [2021-06-16 16:07]:
> >> > > (setq list '(A B C)) ⇒ (A B C)
> >> > > (nconc list '(1 2 3)) ⇒ (A B C 1 2 3)
> >> > > list  ⇒ (A B C 1 2 3)
> >> > 
> >> > Change that to
> >> > 
> >> (let* ((list-1 '(a b c))
> >>         (list-2 (nconc list-1 '(1 2 3))))
> >                    ^^^^ not recommended: '(a b c) is a "constant object"
> >                         Some version of elisp might even refuse to do that!
> 
> True, I wanted to do (list 'a 'b 'c) but I didn't want to change the
> example that much.

That's OK. It works, after all ;-)

I do that all the time, for playing around. But don't do that in
production, that's all.

When publishing as an example, at least, a comment is in order.

In your case, instead of (list 'a 'b 'c), an alternative would
be (copy-sequence '(a b c)).

My comment was there because our current topic is "identity and
mutability", thus it seemed relevant to me. It wasn't to critizice
your code, i /know/ it was just a quick example.

> Also, what versions of elisp wouldn't allow that?

Wait and see :)

I don't think it's planned for now, but I wouldn't exclude it
either, but oh, wait. Have a look at section "E.2 Pure Storage"
of the Emacs Lisp manual. Perhaps there are immutable objects
around, after all :-)

Cheers
 - t

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