File Ports

    Two special procedures work on file ports:

• (flush-output port)     forces all buffered data in the given file output port to be physically written. Buffered data is automatically flushed after each newline. The standard output and error ports are automatically flushed before a character is read from the standard input port. When called on a non-file port, flush-output takes no action. If port is omitted, then the current output port is flushed.
• (file-position port)   returns the current read/write position of the file port port, and (file-position port pos) sets the read/write position to pos. Calling file-position without a position on a non-file input port returns the number of characters that have been read from that port. It is an error to call file-position on a non-file output port, or to call file-position with a position on a non-file input port. (The  exn:application:type exception is raised in these cases.)