Derived enums as bitmap masks

Learning
2

How about this?
(1) use ppx_enumerate to get a list of all flags and values
(2) decode is a simple fold with flag/mask
(3) pp using sexp (reversible) or show

??

open Sexplib0.Sexp_conv

type feature_mask_element =
  | FEATURE1 [@value 1]
  | FEATURE2 [@value 8]
  | FEATURE3 [@value 0x400]
  [@@deriving enum, show, enumerate, sexp]

type feature_mask = feature_mask_element list
  [@@deriving show, sexp]

  let all_masks =
    all_of_feature_mask_element
    |> List.map (fun f -> (f,feature_mask_element_to_enum f))

let decode_features x =
  List.fold_left (fun acc (f,mask) ->
      if x land mask <> 0 then (f::acc) else acc)
    [] all_masks
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