Currency (mina_wire_types.Mina_wire

module Types : sig ... end

module type Concrete =
  Types.S
    with type Fee.V1.t = Unsigned.UInt64.t
     and type Amount.V1.t = Unsigned.UInt64.t
     and type Balance.V1.t = Unsigned.UInt64.t

module M : Types.S

Here, we hide the concrete type definitions from our module, which is the whole point of all this machinery.

module type Local_sig = Utils.Signature(Types).S

module Make
  (Signature : Local_sig)
  (_ : functor (A : Concrete) -> Signature(A).S) : 
  Signature(M).S

Finally, we expose only the types from Types.S but we clarify that the types here are the same that those from M. In some cases this is equivalent to include M.

include Types.S
  with module Fee = M.Fee
   and module Amount = M.Amount
   and module Balance = M.Balance

module Fee = M.Fee

module Amount = M.Amount

module Balance = M.Balance