#!/usr/local/bin/sbcl --script

(defmacro -> (form . forms)
  (if (null forms)
      form
    `(-> ,(nsubst form 'it (car forms)) ,@(cdr forms))))

(defun join-string (lst sep)
  (-> (loop
        :for rest :on (cdr lst)
        :for len := (list-length lst) :then (1- len)
        :until (= len 1)
        :for other := (random len)
        :unless (zerop other)
        :do (rotatef (car rest) (nth other rest))
        :finally (return lst))
      (print it)))

(let ((x (list "a" "b" "c" "d")))
  (print (join-string x " ")))