anchor.diff:    (is-true
      (with-open-socket (s :remote-host *echo-address* :remote-port *echo-port*
                           :address-family :ipv4)
  +     (setf (socket-option s :receive-timeout) *echo-timeout*)
        (and (ipv4-address-p (remote-host s))
             (numberp (remote-port s))))))
   
  
positive.code: 
  (defparameter *echo-address* (ensure-address #(127 0 0 1)))
  (defparameter *echo-port* 7)
  
  ;;;; Addresses
  
  
negative.code:   (is-true
     (with-open-socket (s :remote-host *echo-address* :remote-port *echo-port*
                          :type :datagram :address-family :ipv4)
       (setf (socket-option s :receive-timeout) *echo-timeout*)
       (send-to s #(1 2 3 4 5))
       (let ((nbytes (nth-value 1 (receive-from s :size 200))))
         (plusp nbytes)))))
  