//
// simple demo of using recursive functions to operate on arrays
// (uses higher-order function)
//
println("type in list values (integers), quit to end")
val list = fillList()

println("you entered:")
printList(list)

// try several different ways of using listCombine
println("sum is " + listCombine(list, sum, 0))
println("product is " + listCombine(list, product, 1))
println("sum is " + listCombine(list, (x,y) => x+y, 0))
println("product is " + listCombine(list, (x,y) => x*y, 1))
println("sum is " + listCombine(list, _ + _, 0))
println("product is " + listCombine(list, _ * _, 1))

// also try using it to compute min, max
println("min is " + listCombine(list, (x,y) => (x min y), Int.MaxValue))
println("max is " + listCombine(list, (x,y) => (x max y), Int.MinValue))

def fillList() : List[Int] = {
  val input = readLine
  if (input == "quit") {
    List[Int]()
  }
  else {
    val num = input.toInt
    num :: fillList()
  }
}

def printList(ll : List[Int]) {
  if (!ll.isEmpty) {
    println(ll.head)
    printList(ll.tail)
  }
}

def sum(x : Int, y : Int) : Int = x + y
def product(x : Int, y : Int) : Int = x * y

def listCombine(list : List[Int], 
  combine : (Int, Int) => Int, identity : Int) : Int = 
{
  if (list != Nil) {
    combine(list.head, listCombine(list.tail, combine, identity))
  }
  else {
    identity
  }
}