split7.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

    class Splitter7[T] {
      def splitSimplePass7(seq: List[T]): List[List[T]] = {
        // fails: def isGapType(c : T) = {
        def isGapType[Q <: T](c : Q) = {
          c match {
            case Gap  => true
            case GapN => true
            case _    => false
          }
        }
        val isGap = isGapType(seq(0))
        def isMatch(c : T) = { 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 :: splitSimplePass7(tail)
        }
      }
    }