When with tailrec function

#1

Why tailrec fun do no work with when? It has else branch as if but more clear syntax.

#2

Why do you think it doesn’t work with when?

Here is an example to test the Collatz Conjecture for any number using it:

val two = BigInteger("2")
val three = BigInteger("3")

tailrec fun collatz(a: BigInteger): Unit
    = when
    {
        a == BigInteger.ONE -> Unit
        a.mod(two) == BigInteger.ZERO -> collatz(a / two)
        else -> collatz(a * three + BigInteger.ONE)
    }

(the Collatz Conjecture is that this method will terminate for any positive integer, which has not been proven)