def sumInts(a: Int, b: Int): Double =
  if (a > b) 0 else a + sumInts(a + 1, b)

def sumCubes(a: Int, b: Int): Double =
  if (a > b) 0 else a * a * a + sumCubes(a + 1, b)

def sumRec(a: Int, b: Int): Double =
  if (a > b) 0 else 1.0 / a + sumRec(a + 1, b)

def mapReduce(f: Int => Double, a: Int, b: Int): Double =
  if (a > b) 0 else f(a) + mapReduce(f, a + 1, b)

sumInts(3, 5)
sumCubes(1, 3)
sumRec(1, 3)

mapReduce(i => i, 3, 5)
mapReduce(i => i*i*i, 1, 3)
mapReduce(i => 1.0/i, 1, 3)