Ocaml object system can also achieve this in a quite lightweight way

    type foo = < foo:int >
    type bar = < bar:int >
    type k = < foo; bar >
    type u = < k; baz:int >
    let f (x: <u; ..>) (\* the type annotation is not needed \*) = x#m

The most consistent solution with the least ceremony. Now it is a module, not a type though.

You can create first-class values of this module type, and since values have types, "it" is a type. Specifically, my_foobar has type (module FOOBAR).

Actually getting values out of such a module-typed structure does involve some ceremony, however:

    let f =
      let module M = (val my_foobar) in
      M.foo