You can use $classmethod to invoke any class method, including %New, e.g. 

set cls = "MyPackage.MyClass"
set obj = $classmethod(cls,"%New")

When dealing with stream input, it’s good to keep in mind that strings are limited in length, as explained in the documentaton.

Indeed f j=$i(r)... would get a !! mark if it was a chess move 😉
Congratulations !