(ql:quickload '(chipz archive))

(defun extract-tarball (pathname)
  "Extract a tarball (.tar.gz) file to a directory (*default-pathname-defaults*)."
  (with-open-file (tarball-stream pathname
                   :direction :input
                   :element-type '(unsigned-byte 8))
    (archive::extract-files-from-archive
     (archive:open-archive 'archive:tar-archive
      (chipz:make-decompressing-stream 'chipz:gzip tarball-stream)
      :direction :input))))