car/cdr accessors

compound sequence accessors for nested pairs

These are compound sequence accessors that combine multiple car and cdr operations. The name of each function describes which operations to perform from right to left:

• a represents car (get first element)
• d represents cdr (get rest of list)

Examples

Given a nested list structure:

(define x '((1 2) (3 4)))
(caar x)  ; gets car of (car x) -> 1
(cadr x)  ; gets car of (cdr x) -> (3 4)
(cdar x)  ; gets cdr of (car x) -> (2)
(cddr x)  ; gets cdr of (cdr x) -> ()

;; More deeply nested examples
(define y '((1 2) ((3 4) 5)))
(cadar y)  ; car of (cdr of (car y)) -> 2
(caadr y)  ; car of (car of (cdr y)) -> (3 4)

The functions can access up to 4 levels deep in a nested list structure. Reading from right to left helps understand the access pattern - for example, caddr means “get the first element (car) of the rest of the rest (cddr) of the list”.