mapBetween関数とりあえずやっつけ版

MapBetween.scala

object MapBetween {
  def main(args:Array[String]) = {
    val range = 1 to 10
    println(mapBetween(range, (a1:Int,a2:Int)=>a1+a2))
    println(mapBetween(range, (a1:Int,a2:Int)=>a1*a2))
    println(mapBetween(range, (a1:Int,a2:Int)=>a1-a2))
  }

  def mapBetween[A,B,T>:A](seq:Seq[A], f:(T,T)=>B): Seq[B] = {
    ((Seq[B](), seq.head) /: seq.tail) {(tup:(Seq[B], A), a:A) => (tup._1 :+ f(tup._2, a), a)}._1
  }
}