Re: [Caml-list] intersections of polymorphic variants

[Jeremy Yallop <yallop@gmail.com>]

On 9 February 2017 at 09:52, Martin DeMello <martindemello@gmail.com> wrote:
> In the following code:
>
> type color = [`Red | `Blue | `Green | `Black | `White]
>
> let color_index c = match c with
>   | `Red -> 1
>   | `Blue -> 2
>   | `Green -> 3
>   | `Black -> 4
>   | `White -> 5
>
> type value = [`Red | `Blue | `Green | `Missing]
>
> type state = Color of int | Missing
>
> let state_of_value v = match v with
>   | `Red -> Color (color_index `Red)
>   | `Blue -> Color (color_index `Blue)
>   | `Green -> Color (color_index `Green)
>   | `Missing -> Missing
>
> is there any way to write the last function as
>
> let state_of_value v = match v with
>   | `Red  | `Blue  | `Green -> ?????
>   | `Missing -> Missing

  let state_of_value v = match v with
    | (`Red  | `Blue  | `Green) as c -> Color (color_index c)
    | `Missing -> Missing