Question

Given a list, how would I select a new list, containing a slice of the original list (Given offset and number of elements) ?

EDIT:

Good suggestions so far. Isn’t there something specified in one of the SRFI’s? This appears to be a very fundamental thing, so I’m surprised that I need to implement it in user-land.

Answer 1

The following code will do what you want:

(define get-n-items     (lambda (lst num)         (if (> num 0)             (cons (car lst) (get-n-items (cdr lst) (- num 1)))             '()))) ;'  (define slice     (lambda (lst start count)         (if (> start 1)             (slice (cdr lst) (- start 1) count)             (get-n-items lst count)))) 

Example:

> (define l '(2 3 4 5 6 7 8 9)) ;' () > l (2 3 4 5 6 7 8 9) > (slice l 2 4) (3 4 5 6) >