Recursive types in nested modules

Thanks, I gave up and went for @get instead:

module Foo = {
  type a
  type b

  module A = {
    @get
    external b: a => b = "b"
  }

  module B = {
    @get
    external a: b => b = "a"
  }
}

let a: Foo.a = %raw(`{}`)

let b = a->Foo.A.b