Since combinations of CAR and CDR are frequently used, all combinations up to four uses of CAR and CDR are defined as functions of the form CxxxR:
(CAAR X) = (CAR (CAR X)) (CADR X) = (CAR (CDR X)) (CADDR X) = (CAR (CDR (CDR X)))
It's worth memorizing common combinations:
| CAR | or | FIRST | = | First element of a list |
|
CADR | or | SECOND | = | Second element |
|
CADDR | or | THIRD | = | Third element |
|
CADDDR | or | FOURTH | = | Fourth element |
Functions FIRST through TENTH are defined in Common Lisp.