Auto derive enum conversions

Learning
1

Consider the following code, where all the arms of the enum as “parameter less”

type my_enum = A | B | C | D | E

let _foo (x : my_enum) : int =
  match x with
  | A -> 0
  | B -> 1
  | C -> 2
  | D -> 3
  | E -> 4

let _bar (n : int) : my_enum =
  match n with
  | 0 -> A
  | 1 -> B
  | 2 -> C
  | 3 -> D
  | 4 -> E
  | _ -> failwith "not handled"

This is a bit tedious / error prone to maintain. Is there some ppx that will auto derive _foo / _bar for me ?

2

For foo at least, Obj.magic should do the trick. Otherwise, it should not be too hard to write that ppx yourself

3

ppx_deriving has an enum deriver ? Here’s a bit from the test

type t = Aa | Ba | Ca [@@deriving enum, show]
let test_auto ctxt =
  assert_equal ~printer:string_of_int 0  (to_enum Aa);
  assert_equal ~printer:string_of_int 1  (to_enum Ba);
  assert_equal ~printer:string_of_int 2  (to_enum Ca);
  assert_equal ~printer:show       Aa (get (of_enum 0));
  assert_equal ~printer:show       Ba (get (of_enum 1));
  assert_equal ~printer:show       Ca (get (of_enum 2));
  assert_equal ~printer:string_of_int 0 min;
  assert_equal ~printer:string_of_int 2 max
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