a.ml

module type SA =
sig
  type v

  type t = { value: v }
end

module type SB =
sig
  type v

  module A: SA with type v = v

  type t =
    | A of A.t
    | B
end

module A (S: sig type v end): SA with type v = S.v =
struct
  type v = S.v

  type t = { value: v }
end

module B (S: sig type v end): SB with type v = S.v =
struct
  type v = S.v

  module A: SA with type v = v = A(S)

  type t =
    | A of A.t
    | B
end

module type SC =
sig
  module S: sig type v end

  module B: SB with type v = S.v
                and module A = A(S)
end

module C (S: sig type v end): SC with module S = S and module B = B(S) =
struct
  module B = B(S)
end