module Colour = struct
  type t = { red : int; green : int; blue : int } [@@fieldglass generate]
end

module Legacy = struct
  type t = { value : string } [@@lens generate]
end

let () =
  let colour = Colour.{ red = 3; green = 4; blue = 5 } in
  assert (Colour.red colour = 3);
  assert (Colour.green colour = 4);
  assert (Legacy.value Legacy.{ value = "grey" } = "grey")