Creating streams on files

copy-file.lisp

(defun copy-a-file (origin-path new-path)
  "Copy a file"
  (let ((value-from-read-byte nil))
    ;; create a stream which reads a file
    (with-open-file (origin-file origin-path :direction :input
					     :element-type 'unsigned-byte)
      ;; create a stream which write into a file
      (with-open-file (new-file new-path :direction :output
					 :element-type 'unsigned-byte
					 :if-exists :supersede)
	;; Here we read the origin file and writing into the new file
	(loop
	  ;; exit when get :eof "end of file"
	  (when (equal value-from-read-byte :eof) (return nil))
	  ;; reading the data
	  (setf value-from-read-byte (read-byte origin-file nil :eof))
	  ;; writing the data; in other words copy a file
	  (unless (equal value-from-read-byte :eof)
	    (write-byte value-from-read-byte new-file)))))))