Error: This expression has type
         (string -> string -> 'a, 'b, 'a) format =
           (string -> string -> 'a, 'b, 'a, 'a, 'a, 'a) format6
       but an expression was expected of type
         (string -> float -> 'c, unit, string) format =
           (string -> float -> 'c, unit, string, string, string, string)
           format6
       Type string is not compatible with type float