currying mapreduce example from Martin Odersky's scala course on Coursera https://class.coursera.org/progfun-002/lecture/37

MapReduce.scala

package week2

object product {
  def mapReduce(map:Int=>Int, reduce:(Int,Int)=>Int, init:Int)(a:Int, b:Int): Int = {
		if(a>b) init
		else reduce(map(a), mapReduce(map,reduce,init)(a+1,b))
	}                                         //> mapReduce: (map: Int => Int, reduce: (Int, Int) => Int, init: 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


  def fact(n:Int):Int = product(x=>x)(1,n)        //> fact: (n: Int)Int
  
  fact(4)                                         //> res0: Int = 24
}