gistfile1.n

Main() : void
  {
    def type = "A.B`2+C`1";
    def args = ["X", "Y", "Z"].ToList();
    
    def re = Regex(@"`(\d)");
    
    def sp = re.Split(type.Replace('+', '.'), int.MaxValue);
    
    def sb = StringBuilder();
    mutable posArg;
    for (mutable i = 0; i < sp.Length - 1; i += 2)
    {
      _ = sb.Append(sp[i]);
      
      def argsNum = int.Parse(sp[i + 1]);
      
      _ = sb.Append("[");
      repeat (argsNum)
      {
        _ = sb.Append(args[posArg]);
        _ = sb.Append(",");
        posArg++;
      }
      _ = sb.Remove(sb.Length - 1, 1);
      _ = sb.Append("]");
    }
    
    WriteLine(sb.ToString());