;; Wow, the following function demonstrates use of the run-time
;; property of keyword arguments!
(defun make-pipe-streams (&key (element-type '(unsigned-byte 8)))
  "Return two streams, one for reading and the other for writing.
When elements are written to the write stream, they will be able to be
read by the read stream.  When the write stream is closed, the read
stream will reach the end-of-file."
  (multiple-value-bind (read write) (pipe)
    (flet ((stream-of-type (type fd)
             (make-fd-stream fd
                             :element-type element-type
                             :buffering :none
                             :auto-close t
                             type t)))
      (values (stream-of-type :input read)
              (stream-of-type :output write)))))