Frame 2:26 - Why does conso have a strange cube?

Question

In frame 26 we get the definition for cons⁰:

(degree (conso a d p)
  (== `(,a ■ ,d) p))

The book hasn't mentioned yet what these black cubes are supposed to do. What does it mean?

One hint is in frame 3-4 where it is mentioned that '(d a t e ■ s) is not a proper list.

it says ``(defrel (consO a d p) (== `(,a . ,d) p))``, why have you written `degree`? — Will Ness, Sep 14 '22 at 21:29
it is also used in 2-34 ... 2-36, on the left; 2-40, on the right, where it says `(pear . ())` is a pair, using the same little black square as a dot. — Will Ness, Sep 14 '22 at 21:37
I suspect that you have a digital edition with broken typography. — molbdnilo, Sep 15 '22 at 06:22
@molbdnilo another possibility is that the OP typed the question by hand, selecting the unicode char manually. that would explain the "degree" in place of "defrel" too, due to the auto-correct maybe. — Will Ness, Sep 15 '22 at 08:22
In my book the cons has a superscript 0. Not sure why either. — Alper, Sep 15 '22 at 11:24

Will Ness · Accepted Answer · 2022-09-15T08:19:27.320

2

That's just a dot:

(defrel (cons° a d p) (== `(,a . ,d) p))

The obsession with the quasiquote is quite unhelpful here, in my opinion. It seem much easier to me to read when written as the equivalent

(defrel (cons° a d p) (== (cons a d) p))

edited Sep 15 '22 at 08:19

answered Sep 14 '22 at 21:32

Will Ness

I considered it was a dot but what does a dot mean? – Alper Sep 15 '22 at 11:36
1

Ah, that's a Scheme question. :) it is exactly that which you see here: `(cons 1 2)` prints as `(1 . 2)`, and it also works with the backquote/quasiquote. There should be lots of Q&As about "Scheme dot list" here on SO. – Will Ness Sep 15 '22 at 15:30
1

See e.g. https://stackoverflow.com/search?tab=votes&q=%5bscheme%5d%20dot%20list. – Will Ness Sep 15 '22 at 15:35

1 Answers1