Re: [Caml-list] Who was working on ocaml bindings for zeromq?

[Goswin von Brederlow <goswin-v-b@web.de>]

On Sun, Jan 19, 2014 at 06:16:29PM +0100, Anders Peter Fugmann wrote:
> Hi Goswin,
> 
> Please see my reply below. For completeness your original mail is
> also included in full at the end of the mail.
> 
> On 18/01/14 12:33, Goswin von Brederlow wrote:
> >3) sockets have phantom types, use them
> Agreed.
> 
> >4) Polling is ugly
> Indeed this could be made simpler.

Yesterday I actually run into a problem with this. Creating a socket
gave me a odd type (from memory):

val stream: _[> `Push | `Pull | `Pub | `Sub | `Stream] ZMQ.Socket.t
val dealer: _[> `Push | `Pull | `Pub | `Sub | `Dealer] ZMQ.Socket.t

A few problems with that:

1) A stream socket should be just `Stream.

2) Note the _ there. The type is not polymorphic and gives an error
that it can't be unified or something. Don't have the exact error in
memory.

I think there is something wrong with the way the socket types are
specified that cause this. First time I ever got that kind of error.

3) Polling takes an ('a ZMQ.Socket.t, ZMQ.Socket.event) array. Trying
to poll a stream and dealer socket causes type errors.

I think phantom typed sockets are incompatible with putting them into
an array outside the module. This needs an interface where you have a
poller instance and can add sockets to it one at a time. Internally
the phantom type is known to be "phantom" and the sockets can be put
into an array, hashtbl or list.

I didn't have time yet to look into those problems. Currently I used
Obj.magic to make it work because I wanted to work on the application
instead of on zmq. But that certainly isn't a solution.


So in summary: We need a new polling interface (or phantom typing).
Not just because I don't like it but because it doesn't work for
combining different socket types.

MfG
	Goswin