Polymorphic sum

p.ml

module P = struct
  type t =
    | Null
    | Int of int
    | Float of float

  let sum expr1 expr2 : t =
    match expr1, expr2 with
    | Int a, Int b -> Int (a + b)
    | Float a, Float b -> Float (a +. b)
    | _ -> Null
end

(*
utop # P.sum (P.Int 5) (P.Int 3);;
- : P.t = P.Int 8
utop # P.sum (P.Float 3.5) (P.Float 2.5);;
- : P.t = P.Float 6.
*)