Effective fold() implementation for IndexedSeq

gistfile1.scala

def myFold[A](seq: IndexedSeq[A])(z: A)(f: (A, A) => A): A = {
  // Divide the sequence into to halfes and then combine the results
  def recur(from: Int, to: Int): A = {
    if (from > to) {
      z
    } else if (from == to) {
      seq(from)
    } else {
      f(recur(from, from + (to - from) / 2), recur(from + (to - from) / 2 + 1, to))
    }
  }
  
  recur(0, seq.length - 1)
}

// Performance tests:

val vec = Vector.fill(1000000)("a")
val result = myFold(vec)("")((x, y) => x + y) // Takes 182,0 ms on my machine
val result2 = vec.fold("")((x, y) => x + y) // Doesn't finish in reasonable amount of time