{{works with|Lisaac|0.13.1}}
You can print to standard output in Lisaac by calling STRING.print or INTEGER.print:

Section Header          // The Header section is required.
  + name := GOODBYE;    // Define the name of this object.

Section Public
  - main <- ("Hello world!\n".print;);

However, it may be more straightforward to use IO.print_string instead:

Section Header          // The Header section is required.
  + name := GOODBYE2;   // Define the name of this object.

Section Public
  - main <- (IO.put_string "Hello world!\n";);