Mauricio,

Thanks for your response...


On Mar 25, 2009, at 4:24 PM, Mauricio Fernandez - mfp@acm.org wrote:

> The Lwt.t type is abstract and invariant since no annotation has  
> been given
> for the type variable (you'd need it to be  type +'a t):
>

...

>
> Unfortunately, the type variable is in both variant and  
> contravariant position
> in the definition of Lwt.t...

Just to be sure I understand you... you're saying due to the  
definition/implementation of Lwt and the fact that the type parameter  
cannot be declared covariant, that what I'm trying to do with phantom  
types just can't work in this case. I was afraid of that. :-(

Warren