view.ml

module Foo = struct

  let view = function
    | 0 -> `A
    | 1 -> `B
    | 2 -> `C
    | _ -> `Other

end

module Make1(M : sig val view : int -> [> `A | `B ] end) = struct end
module Make2(M : sig val view : int -> [> `B | `C ] end) = struct end

module M1 = Make1(Foo)
module M2 = Make2(Foo)