(use srfi-1)

(define (slug len)
  (define chars
    "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890")
  (list->string
   (map
    (lambda _
      (string-ref chars (random (string-length chars))))
    (iota len))))