Chapter 8: Fibonacci to PTC form?

[mulongjiangliu]

Loved the in-depth coverage and explanations of this series . And it's easy to understand for newcomers who are fresh to FP.

In Continuation Passing Style (CPS) of Chapter 8, it is said that Fibonacci recursion cannot practically be refactored to pure PTC. It confuses me there. As I find below code, though it lost some readability.

function fib(x, res = 1, pre = 1) { if (x <= 1) return res; return fib(x - 1, pre, pre + res) }

Is above fib a pure PTC form?
Any Comments are welcome and appreciated.