Question

What am I missing here?
This is the error I am getting…

error: type mismatch; found : List[Double](in method
calculateHaarWaveletI)]

required: List[scala.Double]

Console.println(list2Tuples(ls.take(n)))

Here is my code..

    object HaarWavelet {

  def calculateHaarWavelet(ls: List[Double]): List[Double] = {
    if (ls.length % 2 != 0) throw new RuntimeException("Need even number of elements to calculate HaarWavelet")
    calculateHaarWaveletI(ls, ls.length)
    def calculateHaarWaveletI[Double](ls: List[Double], n: Int): List[Double] = {
      Console.println(list2Tuples(ls.take(n)))
      null
    }
    null
  }

  def processTuple(x: (Double, Double)): (Double, Double) = {
    val f = (x._1 + x._2) / 2
    (f, x._1 - f)
  }

  def list2Tuples(ls: List[Double]): List[(Double, Double)] = {
    if (ls.isEmpty) return List()
    (ls.head, ls.tail) match {
      case (_, Nil) => List()
      case (x, y) => List((x, y.head)) ::: list2Tuples(y.tail)
    }
  }

  def main(args: Array[String]) {
    Console.println("Starting....")
    Console.println(calculateHaarWavelet(List(8.0, 4.0)))
    Console.println("Done....")
  }
}

Answer 1

Your type parameter Double in the definition of calculateHaarWaveletI is shadowing scala.Double. You can just remove the type parameter altogether and the code should work as expected. See my answer here for more details.