week2Currying

package example

object week2Currying {

  def mapReduce(f: Int => Int, combine: (Int, Int) => Int, zero: Int)(a: Int, b: Int): Int =
    if (a > b) zero
    else combine(f(a), mapReduce(f, combine, zero)(a + 1, b))
                                                  //> mapReduce: (f: Int => Int, combine: (Int, Int) => Int, zero: Int)(a: Int, b:
                                                  //|  Int)Int

  def product(f: Int => Int)(a: Int, b: Int): Int =
    mapReduce(f, (x, y) => x * y, 1)(a, b)        //> product: (f: Int => Int)(a: Int, b: Int)Int


  def sum (f:Int=>Int)(a:Int,b:Int):Int =
  mapReduce(f, (x,y)=>x+y, 0)(a, b)               //> sum: (f: Int => Int)(a: Int, b: Int)Int

  sum(x=>x*x*x)(2,4)                              //> res0: Int = 99

  def factorial(n: Int): Int = product(x => x)(1, n)
                                                  //> factorial: (n: Int)Int
  factorial(0)                                    //> res1: Int = 1

  product(x => x*x)(3, 4)                         //> res2: Int = 144
  mapReduce(x => x * x, (x, y) => x * y, 1)(2, 4) //> res3: Int = 576
}