//
// demo of some simple functions on lists implemented with loops
//

import scala.io.StdIn._

// get list of doubles from stdin, ending with "quit"
def readList() : List[Double] = {

  // function to prompt for and read input -- put in function to avoid
  // duplication
  def getInput() : String = {
    println("enter next value, 'quit' to end")
    readLine
  }

  var tmp = List[Double]()
  var in = getInput()

  while (in != "quit") {
    // build list in reverse order since that's more efficient, then reverse
    // at end
    tmp = in.toDouble :: tmp
    in = getInput()
  }
  tmp.reverse
}

// print elements of list
def printList(a:List[Double]) {
  for (elem <- a) {
    println(elem)
  }
}

// reduction functions from list-demo rewritten to use loops

// perform reduction on array elements 
// (returns "identity" if size of array is zero)
def combineList(a:List[Double], 
  combine:(Double,Double)=>Double, identity:Double
) : Double = 
{
  var result = identity
  for (elem <- a) {
    result = combine(result, elem)
  }
  result
}

// reduction functions from list-demo

def newSumList(a:List[Double]) : Double = {
  combineList(a, _ + _, 0.0)
}

def newProductList(a:List[Double]) : Double = {
  combineList(a, (x1,x2) => x1*x2, 1.0)
}

def newMaxList(a:List[Double]) : Double = {
  combineList(a, (x1,x2) => x1 max x2, Double.MinValue)
}

def newMinList(a:List[Double]) : Double = {
  combineList(a, (x1,x2) => x1 min x2, Double.MaxValue)
}