isBalanced

gistfile1.scala

  def balance(chars: List[Char]): Boolean = {
    @scala.annotation.tailrec
    def balance(chars: List[Char], stack:List[Unit]): Boolean = (chars, stack) match {
      case (Nil    , Nil) => true
      case (Nil    ,  _ ) => false
      case (')':: _, Nil) => false
      case (head::tail, stack) => head match {
        case '(' => balance(tail, () :: stack)
        case ')' => balance(tail, stack.tail )
        case  _  => balance(tail, stack      ) 
      }
    }  

    balance(chars, Nil)
  }