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Returns #t if object is a list, otherwise returns
#f. By definition, all lists have finite length and are
terminated by the empty list. This procedure returns an answer even for
circular structures.
Any object satisfying this predicate will also satisfy exactly one
of pair? or null?.
(list? '(a b c)) => #t (list? '()) => #t (list? '(a . b)) => #f (let ((x (list 'a))) (set-cdr! x x) (list? x)) => #f
Returns the length of list.
(length '(a b c)) => 3 (length '(a (b) (c d e))) => 3 (length '()) => 0
Returns #t if object is the empty list; otherwise returns
#f (but see section True and False).
(null? '(a . b)) => #f (null? '(a b c)) => #f (null? '()) => #t
Returns the kth element of list, using zero-origin indexing.
The valid indexes of a list are the exact non-negative integers
less than the length of the list. The first element of a list has index
0, the second has index 1, and so on.
(list-ref '(a b c d) 2) => c
(list-ref '(a b c d)
(inexact->exact (round 1.8)))
=> c
(list-ref list k) is equivalent to (car
(list-tail list k)).
Returns the specified element of list. It is an error if
list is not long enough to contain the specified element (for
example, if the argument to seventh is a list that contains only
six elements).
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