Re: [Caml-list] small typing problem with modules ...

[Pietro Abate <Pietro.Abate@pps.jussieu.fr>]

On Tue, May 26, 2009 at 02:37:18PM +0200, Julien Signoles wrote:
> >but then I'm a bit lost putting all this together ... 
> >I know I'm close ... a small hint ?
> Hum, module types cannot be parameterized. If you want to use a functor 
> signature, you can write the following :

uhmmm I was wondering ... :)

> =====
> module type T =
>   functor (Extra : A.Extra) ->
>   functor (A : A.T with type extra  = Extra.t) ->
>   sig val f : A.extra -> unit end
> 
> module Make : T
> 
> open A
> val f : extra -> unit
> =====
> 
> But I'm pretty sure that is not really what is expected...
> However why cannot you just add an another abstract type in your 
> signature like below?

well it does not solve the duplication problem as I cannot write
something like :

include T (A.ExtraDefault) (A)

as we don't have functorized module types as you pointed out. you just
moved the functor signature to the type T ...

> =====
> module type T = sig
>   type extra
>   val f : extra -> unit
> end
> 
> module Make(Extra : A.Extra)(A : A.T with type extra  = Extra.t)
>   : T with type extra = A.extra
> 
> open A
> val f : extra -> unit
> =====

ok, I can do that, but it would be still annoying as the module A might
contain a lot of types that I would need to add to the signature T in
b.mli . Something like :

 module type T = sig
     type a
     type b 
     ...
     type n
     val fa : a -> unit
     val fb : b -> unit
     ...
     val fn : n -> unit
 end    

but this should solve the duplication problem as I can now write
something like

include T with type extra = A.extra ( .... and all other types .... )

I'm still not really satisfied with this solution, but I'm now worried
that with the current syntax is just not possible to solve my problem...

thanks :)
pp