module type MOperDriver = sig
    type value

    val oper : value -> value
end

module MSuccessor (MOD : MOperDriver) = struct

    let soper x = MOD.oper (MOD.oper x)

end

module type MJoinDriver = sig

    type value

    val join : value -> value -> value

end

module MWeird (MOD:MOperDriver) (MJD : MJoinDriver with type value = MOD.value)
    : MOperDriver
    = struct

    module M = MSuccessor(MOD)

    type value = MOD.value


    let oper a  =
        let a' = M.soper a in
        MJD.join a' (MJD.join a' a')

end



type number = Value of int

let nsucc (Value v) = Value (succ v)
let nadd  (Value v) (Value v') = Value (v+v')

module NOperDriver : MOperDriver = struct

    type value = number

    let oper = nsucc

end

module NJoinDriver : MJoinDriver = struct

    type value = number

    let join = nadd
end


module M = MWeird(NOperDriver)(NJoinDriver)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "test.ml", line 62, characters 31-42:
Error: Signature mismatch:
       Modules do not match:
         sig
           type value = NJoinDriver.value
           val join : value -> value -> value
         end
       is not included in
         sig
           type value = NOperDriver.value
           val join : value -> value -> value
         end
       Type declarations do not match:
         type value = NJoinDriver.value
       is not included in
         type value = NOperDriver.value