Phantom types are a programming idiom that can often pull off this sort 
of thing.

--Dan

David Teller wrote:
> On Monday 08 May 2006 05:17, Jacques Garrigue wrote:
> 
>>I would be tempted to say: there is no answer.
>>Ocaml objects are not about enforcing protocols, but about allowing
>>inheritance and structural subtyping, and this does not fit well with
>>your problem.
> 
> 
> Which brings us to a question : how do you enforce protocols in OCaml ?
> 
> Say, is there a "good" way of rewriting file-related operations so that, say, 
> ProtocolUnix.read and ProtocolUnix.write *statically* only accept opened 
> files, and in addition, ProtocolUnix.write only accepts files which have been 
> opened with write priviledges ?
> 
> I mean, there are manners of checking this with, say, model checking tools. In 
> the specific case of file management, I guess we can do it with a little bit 
> of simple subclassing, but I assume there's a large run-time penalty for this 
> extra bit of checking, due to the management of objects by OCaml. Has anyone 
> attempted to determine how well this scales up ? Or explored other options ?
> 
> Cheers,
>  David
> 
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