//
// simple demo of using lists with recursive functions
//

// print elements of list, one per line
def printList(l : List[Int]) {
  if (!l.isEmpty) {
    println(l.head)
    printList(l.tail)
  }
}

// get list of elements read from standard input until "quit"
def inputList() : List[Int] = {
  println("next value?")
  val input = readLine
  if (input == "quit") {
    Nil
  }
  else {
    input.toInt :: inputList()
  }
}

// get sum of elements of list
def sumList(l : List[Int]) : Int = {
  if (!l.isEmpty) {
    l.head + sumList(l.tail)
  }
  else {
    0
  }
}

// get "reduction" of elements of list
// combines elements pairwise using "combine" function, returning
//    identityElement at end of array
def combineList(l : List[Int],
  combine : (Int,Int) => Int,
  identityElement : Int) : Int = 
{
  if (!l.isEmpty) {
    combine(l.head, combineList(l.tail, combine, identityElement))
  }
  else {
    identityElement
  }
}

def add(x:Int, y:Int) : Int = { x + y }
def multiply(x:Int, y:Int) : Int = { x * y }
def smaller(x:Int, y:Int) : Int = { x min y }
def larger(x:Int, y:Int) : Int = { x max y }


println("enter elements for list, 'quit' to end")
val nums = inputList()
printList(nums)
println("sum " + sumList(nums))

println("sum another way:  " + combineList(nums, add, 0))
println("sum yet another way:  " + combineList(nums, (x,y) => x+y, 0))
println("sum yet one more way:  " + combineList(nums, _+_, 0))
println("product:  " + combineList(nums, multiply, 1))
println("minimum:  " + combineList(nums, smaller, Int.MaxValue))
println("maximum:  " + combineList(nums, larger, Int.MinValue))