Start and end must be exact integers satisfying
0 <= start <= end <= (length list)
sublist returns a newly allocated list formed from the elements
of list beginning at index start (inclusive) and ending at
Returns a newly allocated list consisting of the first k elements of list. K must not be greater than the length of list.
We could have defined
list-head this way:
(define (list-head list k) (sublist list 0 k))
Returns the sublist of list obtained by omitting the first k elements. The result, if it is not the empty list, shares structure with list. K must not be greater than the length of list.
Returns a list consisting of the elements of the first list followed by the elements of the other lists.
(append '(x) '(y)) ⇒ (x y) (append '(a) '(b c d)) ⇒ (a b c d) (append '(a (b)) '((c))) ⇒ (a (b) (c)) (append) ⇒ ()
The resulting list is always newly allocated, except that it shares structure with the last list argument. The last argument may actually be any object; an improper list results if the last argument is not a proper list.
(append '(a b) '(c . d)) ⇒ (a b c . d) (append '() 'a) ⇒ a
Returns a list that is the argument lists concatenated together.
The arguments are changed rather than copied. (Compare this with
append, which copies arguments rather than destroying them.) For
(define x '(a b c)) (define y '(d e f)) (define z '(g h)) (append! x y z) ⇒ (a b c d e f g h) x ⇒ (a b c d e f g h) y ⇒ (d e f g h) z ⇒ (g h)
Returns the last pair in list, which may be an improper list.
last-pair could have been defined this way:
(define last-pair (lambda (x) (if (pair? (cdr x)) (last-pair (cdr x)) x)))
These procedures remove the last pair from list. List may
be an improper list, except that it must consist of at least one pair.
except-last-pair returns a newly allocated copy of list
that omits the last pair.
removes the last pair from list and returns list. If the
cdr of list is not a pair, the empty list is returned by either