/*
* Another tail recursive function.  This one sums this items
* in a list of integers.  Note, doing this generically over
* all number types (and only number types) is a pain.  Easiest
* (imo) way is to overload and write independent function for
* each type
* 
* In addition to just doing this TR, we see:
* 1. Kotlin allows default values for function parameters
* 2. Given default values, kotlin allows named parameters in function call
* 3. The "elvis" operator. "?".  This allows the parameter to
* be null.  It also REQUIRES that null be explicitly handled
* This pairling allows Kotlin to be "null safe" 
*
* @author ggtowell
* Created: Aug 2, 2021
 */
fun main() {
    // call with one positional parameter
    println(bb(listOf(1,2,3,4,5)))
    // call with one positional, but it is null
    println(bb(null))
    // call with no params
    println(bb())
    // call with named param
    println(bb(b3=listOf(2,3,4,5,6)))
    // call with other named param
    println(bb(bsum=5))
}

/*
* Recursive function to compute the sum of a list of integers
* Each param has default values so can do anything from all
* positional notation to named to nothing
* @param b3 -- a list of integers : default=null
* @param bsum -- the number to consider to be the sum of an empty or null list: default 0
 */
tailrec fun bb(b3: List<Int>, bsum:Int = 0):Int {
    //if (b3==null) return bsum
    if (b3.isEmpty()) return bsum
    return bb(b3.drop(1), bsum+b3.first())
}