Well but there you only call `callatz_tailrec` onc...

# advent-of-code

[karelpeeters]

Well but there you only call callatz_tailrec once, while in the challenge you need to call it n times.

[joelpedraza]

I’m not sure what you mean. It calls it self more than once (assuming you dont start the recursion with 1)

[joelpedraza]

collatz_tailrec(23) =>

23
70
35
106
53
160
80
40
20
10
5
16
8
4
2
1

[karelpeeters]

I mean that it only calls itself once per iteration.

[joelpedraza]

Ah. Well yes then the first call is’nt in the tail position

[joelpedraza]

My intuition behind how tail call elimination works is: If a recursive call is the tail position it can be replaced with a GOTO. If the function has more work to do it cant just execute a jump back to the top

[karelpeeters]

But then tailrec isn't really applicable in the challenge, both because there's more work to be done after the tail call (constructing the Node) and because you need to call it multiple times.

[joelpedraza]

Exactly correct.