flushes the contents oof the output buffer
INCLUDE 'iolib.h' flush_print_buffer
This predicate causes all contents of the print buffer to be printed to the current output stream. In normal use, the print buffer is flushed after every nl, after 128 characters are stored or when the output is redirected (via writedevice ...). To display single characters, the buffer must be flushed manually.
prolog-process, client-server, object