def combinate(leftovers: List[(Char,Int)]): List[List[(Char,Int)]] = {
      leftovers match {
        case Nil => List()
        case char :: chars =>
            (
            for(n<-0 to char._2) yield
                List( (char._1,n) ) ::: combinate(chars)
            ).toList
      }
    }

Description Resource    Path    Location    Type
type mismatch;  found   : List[List[Product]]  required: List[List[(Char, Int)]]    debug.sc    /progfun-forcomp    line 25 Scala Problem