Re: [Caml-list] Mixing variant types...

[skaller <skaller@users.sourceforge.net>]

On Thu, 2006-01-12 at 12:22 +0900, Jacques Garrigue wrote:

> You can already simulate subtyping using Event.wrap:
>   Event.wrap e (fun x -> (x : t1 :> t2))
> will turn a t1 event into a t2 event.
> (So this probably means that Event.event should be covariant to start
> with...)
> 
> For practical applications, the solution suggested by skaller might be
> satisfactory too.

Err .. but my solution does use Event.wrap .. :

        Event.wrap (receive w.control) (fun (w,e) -> w, (e:> ec))

I just tried making Event.event covariant but it didn't seem to work,
perhaps I did something wrong here?

(* event.ml *)
type +'a event =
    Communication of 'a behavior
  | Choose of 'a event list
  | WrapAbort of 'a event * (unit -> unit)
  | Guard of (unit -> 'a event)

(* event.mli *)
type +'a event

Rebuilt and reinstalled Ocaml 3.09.0 ..  changed example to:

      List.map (fun w ->
        (* Event.wrap (receive w.control) (fun (w,e) -> w, (e:> ec)) *)
         (receive w.control) 
      )
      [] (* !windows .. *)

eliminating the Event.wrap and hoping this would fix it .. 

skaller@rosella:/work/felix/flx$ ocamlc -thread r.ml
File "r.ml", line 28, characters 6-143:
This expression has type (window * event) Event.event list
but is here used with type ws_event list
Type (window * event) Event.event is not compatible with type
  ws_event = (window * ec) Event.event
Type event = [ `Repaint ] is not compatible with type
  ec = [ `New_window | `Repaint ]
The first variant type does not allow tag(s) `New_window

-- 
John Skaller <skaller at users dot sf dot net>
Felix, successor to C++: http://felix.sf.net