[QuadrupleA]

It's kind of silly IMHO. Recursion has plenty of "state", it's added on the stack before each function call. So under the hood it's all stateful. But instead of e.g. a nice simple counter variable, you've got an ever growing pile of stack frames - with hopefully some compiler shenanigans to eliminate them and convert it to a counter internally.

[operator-name]

Just as stateful language can perform tail call optimization, so can functional languages.