module type Format = sig
    type fmt
    val to_int : fmt -> int
end

module type Maker = functor (F : Format) -> sig
    type t
    val unsafe_b : F.fmt -> string
    val unsafe_s : string -> F.fmt
end

module FirstFormat =
    struct
        type fmt = string
        let to_int n = 1
    end

module SecondFormat =
    struct
        type fmt = string
        let to_int n = 2
    end

module Make (F : Format) = struct
    type t = F.fmt
    let unsafe_b (b : F.fmt) = b
    let unsafe_s (s : string) = s
end