I've seen around the following F# definition of a continuation-passing-style fibonacci function, that I always assumed to be tail recursive:

```
let fib k =
let rec fib' k cont =
match k with
| 0 | 1 -> cont 1
| k -> fib' (k-1) (fun a -> fib' (k-2) (fun b -> cont (a+b)))
fib' k id
```

When trying out the equivalent code in Scala, I've made use of the existent @tailrec and was caught off-guard when the Scala compiler informed me the recursive calls are NOT in tail position:

```
def fib(k: Int): Int = {
@tailrec def go(k: Int, cont: Int => Int): Int = {
if (k == 0 || k == 1) cont(1)
else go(k-1, { a => go(k-2, { b => cont(a+b) })})
}
go(k, { x => x })
}
```

I believe my Scala implementation is equivalent to the F# one, so I'm left wondering why the function is not tail recursive?