Merge branch 'null-streams-without-device' into 'master'

      ((os-unix-p) #p"/dev/null")

      ((os-windows-p) #p"NUL") ;; Q: how many Lisps accept the #p"NUL:" syntax?

      (t (error "No /dev/null on your OS"))))

  (defun call-with-null-input (fun &rest keys &key element-type external-format if-does-not-exist)

    "Call FUN with an input stream from the null device; pass keyword arguments to OPEN."

  (defun call-with-null-input (fun &key element-type external-format if-does-not-exist)

    "Call FUN with an input stream that always returns end of file.

The keyword arguments are allowed for backward compatibility, but are ignored."

    (declare (ignore element-type external-format if-does-not-exist))

    (apply 'call-with-input-file (null-device-pathname) fun keys))

    (with-open-stream (input (make-concatenated-stream))

      (funcall fun input)))

  (defmacro with-null-input ((var &rest keys

                              &key element-type external-format if-does-not-exist)

                             &body body)

    (declare (ignore element-type external-format if-does-not-exist))

    "Evaluate BODY in a context when VAR is bound to an input stream accessing the null device.

Pass keyword arguments to OPEN."

    "Evaluate BODY in a context when VAR is bound to an input stream that always returns end of file.

The keyword arguments are allowed for backward compatibility, but are ignored."

    `(call-with-null-input #'(lambda (,var) ,@body) ,@keys))

  (defun call-with-null-output (fun

                                &key (element-type *default-stream-element-type*)

                                  (external-format *utf-8-external-format*)

                                  (if-exists :overwrite)

                                  (if-does-not-exist :error))

    "Call FUN with an output stream to the null device; pass keyword arguments to OPEN."

    (call-with-output-file

     (null-device-pathname) fun

     :element-type element-type :external-format external-format

     :if-exists if-exists :if-does-not-exist if-does-not-exist))

    (declare (ignore element-type external-format if-exists if-does-not-exist))

    "Call FUN with an output stream that discards all output.

The keyword arguments are allowed for backward compatibility, but are ignored."

    (with-open-stream (output (make-broadcast-stream))

      (funcall fun output)))

  (defmacro with-null-output ((var &rest keys

                              &key element-type external-format if-does-not-exist if-exists)

                              &body body)

    "Evaluate BODY in a context when VAR is bound to an output stream accessing the null device.

Pass keyword arguments to OPEN."

    "Evaluate BODY in a context when VAR is bound to an output stream that discards all output.

The keyword arguments are allowed for backward compatibility, but are ignored."

    (declare (ignore element-type external-format if-exists if-does-not-exist))

    `(call-with-null-output #'(lambda (,var) ,@body) ,@keys)))