put_byte(N) writes the byte N to the current output
stream, which must be binary.
put_code(N) writes the character code N to the current output
stream, which must be text.
put_char(A) writes the character atom A to the current output
stream, which must be text.
The byte or character is not necessarily printed immediately; they may be flushed if the buffer is full. See ref-iou-sfh-flu.