//
// simple demo of using recursive functions to operate on arrays
// (uses higher-order function)
//
println("how many values?")
val n = readInt
val a = new Array[Int](n)

fillArray(a, 0)

println("you entered:")
printArray(a, 0)

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

// also try using it to compute min, max
println("min is " + arrayCombine(a, 0, (x,y) => (x min y), Int.MaxValue))
println("max is " + arrayCombine(a, 0, (x,y) => (x max y), Int.MinValue))

def fillArray(aa : Array[Int], startIndex : Int) {
  if (startIndex < aa.size) {
    aa(startIndex) = readInt
    fillArray(aa, startIndex + 1)
  }
}

def printArray(aa : Array[Int], startIndex : Int) {
  if (startIndex < aa.size) {
    println(aa(startIndex))
    printArray(aa, startIndex + 1)
  }
}

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

def arrayCombine(aa : Array[Int], startIndex : Int,
  combine : (Int, Int) => Int, identity : Int) : Int = 
{
  if (startIndex < aa.size) {
    combine(aa(startIndex), arrayCombine(aa, startIndex + 1, combine, identity))
  }
  else {
    identity
  }
}