That's a specific choice that Java designers made, though, not something inherent to checked exceptions in principle. During Project Lambda, one of the proposals - Neal Gafter's - actually had a full-fledged generic exception specification facility that allowed you to define HOFs along the lines of "I throw everything X does, and also Y". They killed it because it was "too complicated".

I agree. Checked exceptions are just a worse version of Result types. I did not intend to make them sound better than they are.

Unchecked exceptions, however, are a different beast entirely. They're not just checked exceptions without the checking; they fundamentally change how you code and how you think about error handling.

Whoa, I've been having opinions about error handling and result types and checked exceptions for like years and I never considered that Java couldn't be "properly" polymorphic over checked exception types. Thanks for pointing that out.

You can use checked exceptions equivalently to Result types in streams e.g. https://github.com/unruly/control/blob/master/src/test/java/...