higher order modules in OCaml

Question

OCaml functors taking an OCaml functor as arguments, or returning OCaml functors are never mentioned in the manual .

Is there a technical reason that prevents OCaml to have higher-order modules?

Answer 1

Higher-order functors are supported and work as expected:

module type endo = sig
  module type t
  module F: t -> t
end
module Twice(F:endo) = struct
  module type t = F.t
  module F(X:t) = F.F(F.F(X))
end

The manual merely considers that it is a not surprising feature.