4.6.8.1 Stream Position Information for Terminal I/O

Input from Prolog streams that have opened the user’s terminal for reading is echoed back as output to the same terminal. This is interleaved with output from other Prolog streams that have opened the user’s terminal for writing. Therefore, all streams connected to the user’s terminal share the same set of position counts and thus return the same values for each of the predicates character_count/2, line_count/2 and line_position/2.