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Re: Cycle Org Shift Select
From: |
tomas |
Subject: |
Re: Cycle Org Shift Select |
Date: |
Tue, 10 Nov 2020 09:08:29 +0100 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Mon, Nov 09, 2020 at 11:49:33PM +0100, Christopher Dimech wrote:
> What is the meaning of the '.' in '#1=(nil t always . #1#)?
This means that the last cdr in that list isn't nil, as "decent,
normal lists" (aka "proper lists") have, but a reference to something,
in this case to the list's head (#1#), which you have taken previously,
in #1=. Making the whole thing an Ouroboros [1].
In box-and-pointer-ish, the list '(nil t always) looks like so
(WARNING: psychedelic effects guaranteed when using variable-pitch
fonts. But who does that, anyway?):
+-----+--+ +--+--+ +--+-----+
| nil | | ---> | | | ---> | | nil |
+-----+--+ +--+--+ +--+-----+
| |
v v
't 'always
Note how the list ends with a pair whose cdr is nil.
The dot notation allows you to fill both slots of a pair (car
and cdr), thus putting something other than the "link to next"
in a cdr, creating an improper list; the reference notation
(that #...= and #...#) allows you to take a ref at some place
and use it later. That's what your above monster looks like
in box-and-pointer:
+---------------------------------+
| |
v |
+-----+--+ +--+--+ +--+--+ |
| nil | | ---> | | | ---> | | | ---+
+-----+--+ +--+--+ +--+--+
| |
v v
't 'always
So if you run *that* list along (by doing cdr), you'll run
in circles, over and over again. That was this device's
intention, anyway, if I followed along correctly.
Cheers
[1] https://en.wikipedia.org/wiki/Ouroboros
- t
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- Re: Cycle Org Shift Select, (continued)
- Re: Cycle Org Shift Select, Christopher Dimech, 2020/11/09
- Re: Cycle Org Shift Select, Noam Postavsky, 2020/11/09
- Re: Cycle Org Shift Select, Michael Heerdegen, 2020/11/09
- Re: Cycle Org Shift Select, Noam Postavsky, 2020/11/09
- Re: Cycle Org Shift Select, Michael Heerdegen, 2020/11/09
- Re: Cycle Org Shift Select, Christopher Dimech, 2020/11/09
- Re: Cycle Org Shift Select, Noam Postavsky, 2020/11/09
- Re: Cycle Org Shift Select, Michael Heerdegen, 2020/11/09
- Re: Cycle Org Shift Select, Christopher Dimech, 2020/11/09
- Re: Cycle Org Shift Select, Christopher Dimech, 2020/11/09
- Re: Cycle Org Shift Select,
tomas <=
- Re: Cycle Org Shift Select, Christopher Dimech, 2020/11/10
- Re: Cycle Org Shift Select, Michael Heerdegen, 2020/11/10
RE: Cycle Org Shift Select, Drew Adams, 2020/11/10
Re: Cycle Org Shift Select, Michael Heerdegen, 2020/11/09