(use srfi-1)
(use srfi-13)

(define (ls pathlist dir)
  (let* ((prefix (string-trim-right dir #[/]))
         (rx (string->regexp #`"^,(regexp-quote prefix)/")))
    (fold (lambda (p rs)
            (or (and-let* ([m (rx p)]
                           [r (regexp-replace* (m'after) #/(?<=\/).*/ "")]
                           [ (not (member r rs)) ])
                  (cons r rs))
                rs))
          '() pathlist)))