Re: Appending lists

[Emanuel Berg via Users list for the GNU Emacs text editor <help-gnu-emacs@gnu.org>]

> Also check out `nconc'
>
> (nconc '(1 2 3) '(4 5) '(6)) ; (1 2 3 4 5 6) - if this works for you, use it
> (nconc '(1 2 3) '(4 5)   6 ) ; (1 2 3 4 5 . 6) - see, last "list" isn't a list!
>
> There was a trick with nconc, you could reverse a list in
> constant time, right? I think that was it but that's all
> I remember.

Probably that wasn't `nconc' but `nreverse', I think!

  (nreverse '(flip six three hole)) ; (hole three six flip)

Yeah, and it didn't take very long either...

Here it says

  Don't use nreverse on quoted list literals; it is undefined
  behavior and may behave in surprising ways, since it is
  de facto self-modifying code. [1]

Hm ... quoted list literals? Is this better?

  (nreverse (list 'flip 'six 'three 'hole)) ; (hole three six flip)

Whats the difference and how does self-modifying code come in?
I did that once but don't remember how it worked. Is that
a function that modifies its own definition when executed?
Funky ... but does that happen here? Where?

But as for reversing the list it seems to "de facto" work
anyway :)

[1] https://stackoverflow.com/a/34423234

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