Exercise 1.4.13

FIRST, REST, and LAST

In addition to car and cdr, it's also possible to manipulate Cons-Cells using the first and rest functions. They're just different names for the same functions. first is the same as car

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

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

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

and rest is the same as cdr

* (cons 1 2)
(1 . 2)

* (cdr (cons 1 2))
2

* (rest (cons 1 2))
2

A third function, last, lets you get at the last Cons-Cell in a particular series.

* (last (cons 1 (cons 2 (cons 3 nil))))
(3)

* (last (cons 1 2))
(1 . 2)

* (last (list 3 4 5))
(5)