Sort a list in scheme

Question

I want to create function which sorts list. For example I have this list:

x1, x2, x3 .... xn

or

1, 2, 3, 4, 5, 6

Answer 1

This is not really a sorting operation, more like a shuffling; here's another way to solve it. First, let's define the interleave procedure that alternates elements from two lists, returning a single list:

(define (interleave l1 l2)
  (cond ((empty? l1) l2)
        ((empty? l2) l1)
        (else (cons (first l1)
                    (interleave l2 (rest l1))))))

Now we take the original list and split-at the middle (this is a Racket-specific procedure); finally we interleave the two resulting lists, reversing the tail:

(define (zippy lst)
  (let-values (((head tail) (split-at lst (quotient (length lst) 2))))
    (interleave head (reverse tail))))

The above implementation IMHO is a bit more intuitive, and if you're working with Racket it doesn't require external libraries. It works as expected:

(zippy '(1 2 3 4 5 6))
=> '(1 6 2 5 3 4)