(defparameter output '())
(loop for char = (read-char nil :EOF)
      ;until (eq char :EOF)
      until (eq char #\Newline)
      do (progn
          ;(format t "input ~A " char)
          (if (alpha-char-p char) (push char output  ))
          (if (digit-char-p char) (setq output (append output (list char))))
          ;(format t "~%")
         )
)

(dolist (x output) (write-char x))
(format t "~%")