Question

I need to create a Scheme function that receives a list and a desired new size, the function then extends the list size by using the same list values. For example:

'(1 2 3) to size 6 will turn to '(1 2 3 1 2 3)
'(1 2) to size 5 will turn to '(1 2 1 2 1)
'(4 5 6 1) to size 7 will turn to '(4 5 6 1 4 5 6)

The new length function parameter can be equal or bigger than the current list size.

Answer 1

You can use SRFI 1 function circular-list (alongside Racket’s built-in take) to do this:

(require srfi/1)
(define (take-circular lst n)
  (take (apply circular-list lst) n))

If you want to avoid using SRFI 1, another method works like this:

(define (take-circular lst n)
  (let ((size (length lst)))
    (if (> n size)
        (append lst (take-circular lst (- n size)))
        (take lst n))))