Practicing the currying lecture of Functional Programming in scala course on coursera.

Currying.scala

object Currying {

   def sum(f: Int => Int) : (Int, Int) => Int = {
     def sumF(a: Int, b: Int) : Int = {
       if(a > b) 0
       else f(a) + sumF(a + 1, b)
     }

     sumF
   }

  def sumOther(f: Int => Int)(a: Int, b: Int): Int = {
    if(a > b) 0 else f(a) + sumOther(f)(a + 1, b)
  }

  def sumInts = sum(x => x)
  def sumCubes = sum(x => x * x * x)


  def id = {x: Int => x}

  def product(f: Int => Int)(a: Int, b: Int): Int = {
    if(a > b) 1 else f(a) * product(f)(a + 1, b)
  }

  def factorial(x: Int) = product(y => y)(1, x)

  def mapReduce(f: Int => Int, combine: (Int, Int) => Int, id: Int)(a: Int, b: Int): Int = {
    if(a > b) id else combine(f(a), mapReduce(f, combine, id)(a + 1, b))
  }

  def fact(n: Int) = mapReduce(x => x, (y, z) => y * z, 1)(1, n)

  def main(args: Array[String]) {
    println(fact(3))
  }
}