Buffered output may need to be flushed e.g. by writing again, by using flush/1, or by closing the stream.
Stream can be a symbolic stream name (atom) or a physical stream number (integer).
Success:
flush(output).
flush(null).
[eclipse]: pipe(in,out), write(out, 'q(a).\n'),
> flush(out), read(in,T).
T = q(a).
yes.
Error:
flush(Stream). (Error 4).
flush("Stream"). (Error 5).
flush(12). (Error 192). % no such stream
flush(debug_input). (Error 192). % input stream