strange.ml

module X: sig
  type +'a t
  val one: [`one of _ ] t
  val two: [`two of _ ] t
  val match':
    [< `one of 'r & 'a | `two of 'r & 'b] t -> 'a -> 'b -> 'r
end = struct
  type 'a t = One | Two
  let one = One
  let two = Two
  let match' value branch_1 branch_2 =
    match value with
    | One -> Obj.magic branch_1
    | Two -> Obj.magic branch_2
end
open X

let f x = match' x 1 1.

let g x y =
  f x + f y
let x = f one + 1
let y = f two +. 1.
let () = Format.printf "Test:%d %f %d@." (f one) (f two) (g one one)
(* error
;; f two + 1
;; f one +. 1
*)