On Fri, 2006-01-13 at 13:57 +0900, Jacques Garrigue wrote:
> From: skaller <skaller@users.sourceforge.net>
>> (* 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)

> The + above is not needed (it is implied by the definition)

But it would fail if the type is not in fact covariant
in its argument?

> You still need to coerce the resulting list:
> (List.map (fun w -> receive w.control) !windows :> ws_event list)

Still doesn't seem to work: OUCH! Yes it DOES. Argg..
I modified

otherlibs/threads/event.*

but I didn't modify

otherlibs/systhreads/event.*

So when I compile with -thread it doesn't work.
But when I compile with -vmthread it does work.
Which is pretty conclusive proof the patch does work
in at least one case. And if I'm right, the + in 
the implementation proves covariance mechanically so
it should be safe.

Should I add a feature request to the bug tracker?

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