car and cdr

car and cdr are 2 main list primitives in lisp. In elisp, there are also cadr-like macros that is the short hand of using them in a row. Basically, everything in lisp is cons cells, consist of a car and a cdr, that is a head and a tail.

	cons cell '(1 . 2)	list '(1 2)	list of one '(1)
car	1	1	1
cdr	2	'(2)	nil

cadr-like macros are interpreted as (car (cdr X)). They are useful to:

• get value from nested list like '((1)) (caar) or '(nil (1)) (caadr => 1)
• discarding some head elements like in '(nil nil nil nil 1 2), (cddddr => '(1 2))
• act like second or third but cooler and more cryptic (cadr = second; caddr = third)