anchor.diff:  
           let rec parse_obj (acc : (string * JSON) list) (tokens : Token list) : (JSON * Token list) = 
               match tokens with
  -            | String name :: Colon :: Null :: ts ->
  +            | String name :: Colon :: Null :: ts -> /// переписать, как на семинаре - разбирать эту случаи два раза в parse и parseObj не нужно!
                   parse_obj ((string name, JSON_Null) :: acc) ts
               | String name :: Colon :: String s :: ts ->
                   parse_obj ((string name, JSON_String s) :: acc) ts
  
positive.code:     let rec parse' (tokens : Token list) : (JSON * Token list) =
          let rec parse_list (acc : JSON list) (tokens : Token list) : (JSON * Token list) =
              match tokens with
              | Null :: ts ->
                  parse_list ((JSON_Null) :: acc) ts
              | String s :: ts ->
                  parse_list ((JSON_String s) :: acc) ts
  
negative.code:     | JSON_Boolean of bool
      | JSON_List of JSON list
      | JSON_Obj of (string * JSON) list
     ******)))))
       
  let rec stringify (json : JSON) : string =
      let s_name (s : string) : string = "\"" + s + "\""
  