▼Unstable
On this page:
list-prefix?
filter-multiple
extend
check-duplicate
map/ values
remf
  top← prev  up  next → 

11 Lists

 (require unstable/list)

This library is unstable; compatibility will not be maintained. See Unstable for more information.

(list-prefix? l r) → boolean?
  l : list?
  r : list?
True if l is a prefix of r.

Example:

  > (list-prefix? '(1 2) '(1 2 3 4 5))

  #t

The subsequent bindings were added by Sam Tobin-Hochstadt.

(filter-multiple l f ...) → 
list? ...
  l : list?
  f : procedure?
Produces (values (filter f l) ...).

Example:

  > (filter-multiple (list 1 2 3 4 5) even? odd?)

  '(2 4)

  '(1 3 5)

(extend l1 l2 v) → list?
  l1 : list?
  l2 : list?
  v : any/c
Extends l2 to be as long as l1 by adding (- (length l1) (length l2)) copies of v to the end of l2.

Example:

  > (extend '(1 2 3) '(a) 'b)

  '(a b b)

The subsequent bindings were added by Ryan Culpepper.

(check-duplicate lst    
  [#:key extract-key    
  #:same? same?]) → (or/c any/c #f)
  lst : list?
  extract-key : (-> any/c any/c) = (lambda (x) x)
  same? : 
(or/c (any/c any/c . -> . any/c)
      dict?)
 = equal?
Returns the first duplicate item in lst. More precisely, it returns the first x such that there was a previous y where (same? (extract-key x) (extract-key y)).

The same? argument can either be an equivalence predicate such as equal? or eqv? or a dictionary. In the latter case, the elements of the list are mapped to #t in the dictionary until an element is discovered that is already mapped to a true value. The procedures equal?, eqv?, and eq? automatically use a dictionary for speed.

Examples:

  > (check-duplicate '(1 2 3 4))

  #f

  > (check-duplicate '(1 2 3 2 1))

  2

  > (check-duplicate '((a 1) (b 2) (a 3)) #:key car)

  '(a 3)

  > (define id-t (make-free-id-table))
  > (check-duplicate (syntax->list #'(a b c d a b))
                     #:same? id-t)

  #<syntax:10:0 a>

  > (dict-map id-t list)

  '((#<syntax:10:0 d> #t) (#<syntax:10:0 a> #t) (#<syntax:10:0 b> #t) (#<syntax:10:0 c> #t))

The subsequent bindings were added by Carl Eastlund.

(map/values n f lst ...) → 
(listof B_1) ... (listof B_n)
  n : natural-number/c
  f : (-> A ... (values B_1 ... B_n))
  lst : (listof A)
Produces lists of the respective values of f applied to the elements in lst ... sequentially.

Example:

  > (map/values
     3
     (lambda (x)
       (values (+ x 1) x (- x 1)))
     (list 1 2 3))

  '(2 3 4)

  '(1 2 3)

  '(0 1 2)

The subsequent bindings were added by David Van Horn.

(remf pred lst) → list?
  pred : procedure?
  lst : list?
Returns a list that is like lst, omitting the first element of lst for which pred produces a true value.

Example:

  > (remf negative? '(1 -2 3 4 -5))

  '(1 3 4 -5)

  top← prev  up  next →