cfunction (file/seek f &opt whence n) Jump to a relative location in the file. 'whence' must be one of :cur - jump relative to the current file location :set - jump relative to the beginning of the file :end - jump relative to the end of the file By default, 'whence' is :cur. Optionally a value n may be passed for the relative number of bytes to seek in the file. n may be a real number to handle large files of more the 4GB. Returns the file handle.