Exercise 1.4.2

Consing

As we saw in the previous exercise, Cons-Cells can be created with the cons function. This operation is called consing.

In the REPL

Let's try consing a few pairs of objects together.

(cons 'a 'b)

(cons 1 2)

(cons "one" "two")

What You Should See

The cons function returns a fresh Cons-Cell every time it is called. Since a Cons-Cell is just a pair of pointers it can combine any two Lisp objects into a pair, no matter what their type is.

* (cons 'a 'b)
(A . B)

* (cons 1 2)
(1 . 2)

* (cons "one" "two")
("one" . "two")

Notice the special syntax of the Cons-Cell returned at the REPL? This is called Dot-Notation and we'll learn more about it in the next exercise.