CAR And CDR
car ( /ˈkɑr/) and cdr (/ˈkʌdər/ or /ˈkʊdər/) are primitive operations on cons cells (or "non-atomic S-expressions") introduced in the Lisp programming language. A cons cell is composed of two pointers; the car operation extracts the first pointer, and the cdr operation extracts the second.
Thus, the expression (car (cons x y)) evaluates to x, and (cdr (cons x y)) evaluates to y.
When cons cells are used to implement singly linked lists (rather than trees and other more complicated structures), the car operation returns the first element of the list, while cdr returns the rest of the list. For this reason, the operations are sometimes given the names first and rest or head and tail.
Read more about CAR And CDR: Etymology, Other Computer Languages
Famous quotes containing the word car:
“Raising children is a spur-of-the-moment, seat-of-the-pants sort of deal, as any parent knows, particularly after an adult child says that his most searing memory consists of an offhand comment in the car on the way to second grade that the parent cannot even dimly recall.”
—Anna Quindlen (b. 1952)