open_null_stream/1open_null_stream(-Stream)
opens an output text stream that is not connected to any file and unifies its stream object with Stream.
Characters or terms that are sent to this stream are thrown away.
This predicate is useful because various pieces of local state are
kept for null streams: the predicates
character_count/2, line_count/2, and
line_position/2 can be used on these streams.