Kotlin - recursive function -2 : TCE

class KotlinPlayGroundActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_kotlin_play_ground)

        val lists = listOf('a', 'f', 'd', 'w')
        println("toString : ${toString(lists)}")

        println("add : ${add(10, 15)}")
        println("addSecond : ${addSecond(10, 15)}")

        println("factorialFirst : ${Factorial.factorialFirst(5)}")
        println("FactorialSecond : ${FactorialSecond.factorialSecond(3)}")
        println("factorialBigInteger : ${factorialBigInteger(BigInteger.valueOf(35))}")

    }

    fun toString(list: List<Char>): String {
        tailrec fun toString(list: List<Char>, s: String): String =
            if (list.isEmpty())
                s
            else
                toString(list.subList(1, list.size), append(list[0], s))

        return toString(list, "jh")
    }

    fun append(c: Char, s: String): String = "$s $c"

    fun inc(n: Int) = n + 1
    fun dec(n: Int) = n - 1

    fun add(a: Int, b: Int): Int {
        var x = a
        var y = b

        while (true) {
            if (y == 0) return x
            x = inc(x)
            y = dec(y)
        }

    }

    tailrec fun addSecond(x: Int, y: Int): Int =
        if (y == 0)
            x
        else
            addSecond(inc(x), dec(y))


    object Factorial {
        lateinit var factorialFirst: (Int) -> Int

        init {
            factorialFirst = { n -> if (n <= 1) n else n * factorialFirst(n - 1) }

        }
    }

    object FactorialSecond {

        val factorialSecond: (Int) -> Int by lazy {
            { n: Int ->
                if (n <= 1) n else n * factorialSecond(n - 1)
            }
        }
    }

    fun factorialBigInteger(n: BigInteger): BigInteger =
        if (n == BigInteger.ONE)
            BigInteger.valueOf(1)
        else
            n * factorialBigInteger(n - BigInteger.ONE)
    
}