addition chain in scala - failing and flailing

addition_chain.scala

import scala.annotation.tailrec

object AdditionChain {
  def chain(len:Int, target:Int):List[List[Int]]= {
    def inner(len:Int, target:Int, sofar:List[Int]):List[Int] = {
      sofar.length == len match {
        case true => 
          println(sofar)
          sofar.head == target match {
            case true => sofar
            case false => inner(len, target, List(1))
          }
        case false => sofar.
                      map(x => x + sofar.head).
                      map(x => (x::sofar).sorted.reverse).
                      map(x => inner(len, target, x)).
                      flatten
        }
      }    
    inner(len, target, List(1)).grouped(len)toList
  }
  
  def main(args:Array[String]) = {
    println(chain(args(1).toInt, args(2).toInt))
  }
}