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Re: Appending lists
From: |
Emanuel Berg |
Subject: |
Re: Appending lists |
Date: |
Tue, 15 Jun 2021 10:27:48 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux) |
> 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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