NoValue Value

The NoValue class implements a void and silent value returned by setListenerSel() to prevent "OK" from being printed to the listener.

There is one distinguished instance of the NoValue class in the reserved system variable silentValue.

You can return silentValue from a function and it will prevent anything from being printed in the listener, including an concluding "OK" and any output sent to format() or print().

For Example

   fn loudFunc = (    format "I'm printing something")
   fn quietFunc = (format "I won't print anything"; return silentValue)

   loudFunc()
   quietFunc()

   --> output:
   loudFunc()
   quietFunc()
   I'm printing somethingOK