split4.scala

    case class Symbol()
    case object Gap extends Symbol
    case class Nucleotide() extends Symbol
    case object GapN extends Nucleotide
    case object A extends Nucleotide
    case object G extends Nucleotide
    case object C extends Nucleotide
    case object T extends Nucleotide
    def splitSimplePass4(seq: List[Symbol]): List[List[Symbol]] = {
      val gap = GapN
      val isGap = (seq(0) == gap)
      def isMatch(c : Symbol) = { if (isGap) c == gap else c != gap }
      val s = seq.takeWhile{ isMatch }
      val tail = seq.takeRight(seq.length - s.length)
      tail match {
        case Nil => s :: Nil
        case _   => s :: splitSimplePass4(tail)
      }
    }