Add a new function that returns a value, so that it can be called from Yarn scripts.
public void AddFunction<T1, TResult>(string name, System.Func<T1, TResult> implementation);
When this function has been registered, it can be called from your Yarn scripts like so:
<<if myFunction(1, 2) == true>>
myFunction returned true!
callcommand can also be used to invoke the function:
<<call myFunction(1, 2)>>