[forgot reply all] zip is unnecessary because of n-ary map. (zip l0 l1) = (map list l0 l1) -Ian ----- Original Message ----- From: "Diogo F. S. Ramos" <diogo...@gmail.com> To: dev@racket-lang.org Sent: Thursday, November 8, 2012 11:46:15 PM GMT -05:00 US/Canada Eastern Subject: [racket-dev] [PATCH] Add a `zip' procedure to lists
`zip' gathers together each element of each list, in order, returning a list of those elements. For example: (zip (list 4 2) (list 3 5)) => '((4 3) (2 5)) Every list has to have the same length. --- There was talk in the IRC about implementing a `zip' procedure. Here is my try. Unfortunately I still don't know what is the preferred way to check for the validity of the parameters. I tried to copy the style of the rest of the file. collects/racket/list.rkt | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/collects/racket/list.rkt b/collects/racket/list.rkt index fe32f68..18055e5 100644 --- a/collects/racket/list.rkt +++ b/collects/racket/list.rkt @@ -32,7 +32,8 @@ append-map filter-not shuffle - range) + range + zip) (define (first x) (if (and (pair? x) (list? x)) @@ -407,3 +408,9 @@ [(end) (for/list ([i (in-range end)]) i)] [(start end) (for/list ([i (in-range start end)]) i)] [(start end step) (for/list ([i (in-range start end step)]) i)])) + +(define (zip list1 list2 . lists) + (for ((l (list* list1 list2 lists))) + (unless (list? l) + (raise-argument-error 'zip "list?" l))) + (apply map list (list* list1 list2 lists))) -- 1.7.9.5 _________________________ Racket Developers list: http://lists.racket-lang.org/dev _________________________ Racket Developers list: http://lists.racket-lang.org/dev