car, cdr - the car or cdr field of a pair (head and tail)

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LIBRARY

(import (rnrs))                     ;R6RS
(import (rnrs base))                ;R6RS
(import (scheme base))              ;R7RS

SYNOPSIS

(car pair)
(cdr pair)

DESCRIPTION

These procedures can also be used with lists, which in Scheme are linked lists of pairs. The car procedure returns the head of a list. The cdr procedure returns the tail of a list.

RETURN VALUES

ERRORS

&assertion (R6RS)

The argument is not a pair.

&assertion (R6RS)

The wrong number of arguments was passed.

R7RS

The situations described above are errors. Implementations may signal an error, extend the procedure's domain of definition to include such arguments, or fail catastrophically.

STANDARDS

EXAMPLES

(car '(a b c))      => a
(car '((a) b c d))  => (a)
(car '(1 . 2))      => 1
(car '())           => &assertion exception

(cdr '((a) b c d))  => (b c d)
(cdr '(1 . 2))      => 2
(cdr '())           => &assertion exception

SEE ALSO

HISTORY

AUTHORS