Re: [External] : Re: Chopping the last element of a list

[address@hidden]

On Fri, Apr 29, 2022 at 03:55:39PM +0000, Drew Adams wrote:
> > > > Here. It returns the last element, and it
> > > > chops that last element off the list.
> > >
> > > Thanks. It's quite simple and useful  to have along with
> > > last/butlast/etc.
> > >
> > > Will you put it into subr.el, so emacs has it built-in ?
> > 
> > Read Drew's code again. Read the examples he provided.
> > 
> > Now, answer this one question: for a list with exactly
> > one element, say
> > 
> >   (setq foo '(1))
> > 
> > what is its last element? What would you expect choplast
> > to do? What does Drew's implementation do? Surprise?
> 
> Yes.  If you want to return 1 in that case then
> be aware that there's no way to modify a cons
> to turn it into nil.  (nil is a scalar - what
> Lisp calls an "atom"; a cons is not.)

I know...

> I intentionally kept the same behavior as `butlast':
> return nil and don't change anything for a list
> with less than 2 elements.

...and I know you know :)

I wanted to help OP to understand why changing things "in
place" has this special feel about it in Lisp land :-)

Cheers
-- 
t

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