(defun concurrency-example (&optional (out *standard-output*))
  (let ((lock (bordeaux-threads:make-lock)))
    (flet ((writer (string)
             #'(lambda ()
                 (bordeaux-threads:acquire-lock lock t)
                 (write-line string out)
                 (bordeaux-threads:release-lock lock))))
      (bordeaux-threads:make-thread (writer "Enjoy"))
      (bordeaux-threads:make-thread (writer "Rosetta"))
      (bordeaux-threads:make-thread (writer "Code")))))