It starts to get more complex than you might think. Suppose I declare x to be of interface type A and then pattern match it to a disjoint interface type B. Now

It starts to get more complex than you might think. Suppose I declare x to be of interface type A and then pattern match it to a disjoint interface type B. Now unless I get depresse that with a cast or a new variable name then I need to express it as some kind of intersection type and this may need to extend into the bytecode and vm. It might even be an intersection between an object and an interface type, and for historical reasons those have different bytecodes for invoking methods! Flow typing is really cool, but it can make things way more complex.