Re: [Caml-list] Expanding functors

[Drup <drupyog+caml@zoho.com>]

Le 27/08/2015 15:29, Yotam Barnoy a écrit :
> One problem I've commonly encountered in OCaml is the inability to 
> expand the interface of functors after they've been created (I'm not 
> talking about post-application). For example, Map.Make in the stdlib 
> takes an OrderedType module which contains only the compare function. 
> What happens if I want to add something to this interface, such as a 
> show function? I have to copy the whole implementation of Map.Make 
> into my own file to modify it. Compare this to the ability to 
> 'include' a regular module and just add the new functionality, and to 
> take the type of a module and expand that type as needed. Functors are 
> severely lacking in this regard.
>
> What do people think of this idea -- of allowing functors to be 
> expanded? Ideally, expanding a functor would allow for both replacing 
> its argument type (as in the example I gave) and for adding a 
> second/third functor argument type (so Map.Make(OrderedType) would 
> become Map.Make(OrderedType)(Show).
>
> -Yotam

module Make(O : Map.OrderedType) = struct
   include Map.Make(O)
   let foo = ....
end

You successfully extended Map without breaking anyone's code !