[dudul]

It's kind of cute to see Java practitioners discover what has been around in many functional languages for literally decades :)

But, hey, if it helps make Java code cleaner and safer (and Optional and Either definitely help a lot with that), I'm all for it.

[jfoutz]

The oldest version I can think of was Konrad Zeus's architecture for real computers. Sigma with index variables forcing an expression to zero capture the same concept. Pretty sure that is an old old idea.

Who did it first can be interesting, but it's rarely much use.