Exercise 1.4.5

CAR and CDR

Using Cons-Cells as building blocks would be kind of pointless if we couldn't get their components back out. To get the value of the first slot in a Cons-Cell, we use the car function.

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

* (car (cons 'a 'b))
A

Similarly, we can get the value from the second slot in a Cons-Cell using cdr.

* (cons 1 2)
(1 . 2)

* (cdr (cons 1 2))
2