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Date: Mon, 01 Feb 2010 23:12:12 +0100
From: Tiphaine Turpin <Tiphaine.Turpin@irisa.fr>
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To: Goswin von Brederlow <goswin-v-b@web.de>
Cc: caml-list@yquem.inria.fr
Subject: Re: [Caml-list] Problem correlating input and output type
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X-Spam: no; 0.00; irisa:01 irisa:01 callbacks:01 runtime:01 runtime:01 ocaml:01 ocaml:01 trivial:01 functors:01 recursive:01 typing:01 typing:01 caml-list:01 dependency:01 imperative:01 

Goswin von Brederlow a écrit :
> Tiphaine Turpin <Tiphaine.Turpin@irisa.fr> writes:
>
>   
>> Goswin von Brederlow a écrit :
>>     
>>> [...]
>>>
>>> Can anyone think of a way to express this so that the type system keeps
>>> track of which callbacks are already connected?
>>>   
>> Runtime checking would be much easier (but still a bit hackish).
>>     
>
> But runtime checks will only show the error when the GUI object is
> instantiated. Some obscure dialog might not pop up in month.
[...]
> But how do you translate that into ocaml objects?
>
>   
I see two requirements in your problem that are difficult to combine:
- static checking by an "ordinary" type system
- dynamic connection of objects.

First, I believe that it prevents anything imperative (because such
typing ignores the execution flow). A functional approach may succeed in
some sense, but I don't think that it would be practical. As for the
combination with objects, In my (humble) experience with objects in
Ocaml, I found that typing even reasonably simple designs is not a
trivial task. So, combining that with the earlier hack would quickly
become a nightmare.

My personal opinion would be to drop the second condition, and make the
connection of your objects static. I would try to define the objects as
functors, with one module parameter per connection, and connect all that
using (possibly recursive) module definitions.

I'm curious to know what solutions object-oriented people could propose,
in particular with dependency injection.

Tiphaine