Fair enough, my bad - that definition is what I use as well. I think I got a bit stuck up when OP said "aren't really required", because for the definition that

Fair enough, my bad - that definition is what I use as well. I think I got a bit stuck up when OP said "aren't really required", because for the definition that's true, but for real world usage, it is required in pretty much every pure FP language that I know.