             if checker(self[index]) {
                 break
             }
-            index = characters.index(after: index)
+            index = self.index(after: index)
         }
         return index
     }

        var result = ""

        if self[index] == "-" {
            index = characters.index(after: index)
            result = "-"
        }


    }

    func findBlock(_ start: String.Index, startSign: String, endSign: Character, needFormat: Bool) throws -> (string: String, index: String.Index) {
        var index = self.index(after: start)
        var result = startSign
        while index < endIndex {
            let next = self[index]
