Tail recursive binary search in Kotlin

tailrec fun <T : Comparable<T>> binarySearch(list: List<T>, item: T, startIndex: Int = 0, endIndex: Int = list.size - 1): Int {
    if (endIndex < startIndex ) {
        return -1
    } else if (startIndex == endIndex) {
        return if (item == list[startIndex]) startIndex else -1
    } else if (endIndex == startIndex + 1) {
        if (list[startIndex] == item) {
            return startIndex
        }
        else if(list[endIndex] == item) {
            return endIndex
        }
        return -1
    } else {
        val midIndex = (endIndex - startIndex) / 2 + startIndex
        val midValue = list[midIndex]
        val (newStartIndex, newEndIndex) = if (item < midValue) Pair(startIndex, midIndex) else Pair(midIndex, endIndex)
        return binarySearch(list, item, newStartIndex, newEndIndex)
    }
}


val list = arrayListOf(1, 2, 3, 4, 5, 10)

fun main(args: Array<String>) {

    assert(binarySearch(list, 1) == 0)
    assert(binarySearch(list, 2) == 1)
    assert(binarySearch(list, 5) == 4)
    assert(binarySearch(list, 10) == 5)
    assert(binarySearch(list, 11) == -1)
    assert(binarySearch(list, 6) == -1)
}

fun assert(value: Boolean) {
    if (!value) {
        throw AssertionError("Value was false")
    }
}