Question

Why lists created with cons() and list() are shown differently despite the lists are equal? The first one shows items separated by dot, but second one do w/o.

> (cons 1 2)
(1 . 2)

> '(1 2)
(1 2)

I know that cons constructs dotted pair, but in this case the lists are same but shown differently.

Answer 1

To expand on Basile’s answer:

(1 2)

is a proper list of length two. That is, it contains two cons cells:

#1=(1 . #2#)
#2=(2 . ())

On the other hand,

(1 . 2)

is an improper list of length one. That is, it contains one cons cell:

#1=(1 . 2)

A non-empty proper list is a list where the last cons cell’s cdr that contains the empty list, (). A non-empty improper list is a list where the last cons cell’s cdr contains anything else.