split5.scala

    case class Symbol() {
      def isGap() = false
    }
    case object Gap extends Symbol {
      override def isGap() = true 
    }
    case class Nucleotide() extends Symbol
    case object GapN extends Nucleotide {
      override def isGap() = true 
    }
    case object A extends Nucleotide
    case object G extends Nucleotide
    case object C extends Nucleotide
    case object T extends Nucleotide
    def splitSimplePass5(seq: List[Symbol]): List[List[Symbol]] = {
      def isGapType(c : Symbol) = c.isGap()
      val isGap = isGapType(seq(0))
      def isMatch(c : Symbol) = { if (isGap) isGapType(c) else !isGapType(c) }
      val s = seq.takeWhile{ isMatch }
      val tail = seq.takeRight(seq.length - s.length)
      tail match {
        case Nil => s :: Nil
        case _   => s :: splitSimplePass5(tail)
      }
    }