fcn evalWithX(text,x) {
   f:=Compiler.Compiler.compileText(text);
   f.x = x; // set free var in compiled blob
   f.__constructor(); // run blob
   vm.regX   // compiler sets the VMs X register for cases like this
}
const TEXT="var x; x*2"; // variables need to be declared
evalWithX(TEXT,5) - evalWithX(TEXT,3) #--> 4