the shortest snake arrange algorithm (slow version)

ft1.scm

(define (main . args)
  (let* ((ll ((@ (srfi srfi-1) iota) (read) 1)) (len (length ll)) (m (1- (/ len 2))))
    (display len)(newline)
    (let lp((a (list-head ll (1+ m))) (b (list-tail ll (1+ m))) (n 1))
      (and (< n len) (for-each (lambda (x y) (display x)(display " ")(display y)(display " ")) a b)(newline)
           (lp `(1 ,(car b) ,@(cdr a)) `(,@(cdr b) ,(list-ref a m)) (1+ n))))))