verifying balanced parens with recursion

balance.scala

    def balance(chars: List[Char]): Boolean = {
      def balanced(chars: List[Char], currently_open_parens: Int): Boolean = {
        if (chars.isEmpty) currently_open_parens == 0
        else {
          if(chars.head == '(') balanced(chars.tail, currently_open_parens+1)
          else {
            if(chars.head == ')' ) {
              currently_open_parens > 0 && balanced(chars.tail, currently_open_parens-1)
            } else balanced(chars.tail, currently_open_parens)
          }
        }
      }
      balanced(chars,0)
    }

or another way to do it with no rec, but has a flaw

def balance(s: String): Boolean ={
    return s.toList.map(c => {
      c match {
        case '(' => 1
        case ')' => -1
        case _ => 0
      }
    }).sum == 0
  }