Cons in

About Cons

Conses are a basic data type in Common Lisp. They are composed of a head and a tail (called for historical reason the car and the cdr). There is no restriction on the data types of the head and tail of a cons.

Conses are created with the cons function which takes two objects and evaluates to a cons (also sometimes termed a 'cons cell').

The parts of a cons may be accessed with the functions car and cdr.

Reference

;; Testing for atoms
(atom 'foo)              ; => T
(atom '(bar baz))        ; => NIL

;; Testing for cons
(consp 'foo)             ; => NIL
(consp '(bar baz))       ; => T

;; First item of a cons
(car '(one two three))   ; => ONE
(first '(one two three)) ; => ONE

;; Rest of a cons
(cdr '(one two three))   ; => (TWO THREE)
(rest '(one two three))  ; => (TWO THREE)