Click here for the syntax and equivalence chart of all car and cdr compositions.
Functions are provided which perform compositions up to four car and cdr operations. Their names consist of a
C, followed by two, three or four occurrences of
D, and finally a
R. The series of
Ds in each function's name is chosen to identify the series of car and cdr operations that is performed by the function. The order in which the
Ds appear is the inverse of the order in which the corresponding operations are performed.
setf can also be used with any of these functions to change an existing component of x, but setf will not make new components. So, for example, the car of a cons can be assigned with setf of car, but the car of nil cannot be assigned with setf of car.
Similarly, the car of the car of a cons whose car is a cons can be assigned with setf of caar, but neither nil nor a cons whose car is nil can be assigned with setf of caar. The argument x is permitted to be a dotted list or a circular list.
(cdr '(1 . 2))
(cdr '(1 2))
(cadr '(1 2))
(car '(a b c))
(cdr '(a b c))
The functions car and cdr should signal type-error if they receive an argument which is not a list. The other functions (caar, cadr, ..., cddddr) should behave for the purpose of error checking as if defined by appropriate calls to car and cdr.
To be done.