How do I take a slice of a list (A sublist) in scheme?

lisp, scheme

Solution

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)
>

Problem

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.

Original source