Re: [Caml-list] Default methods for module signatures

[Alain Frisch <alain@frisch.fr>]

I proposed (13 years ago...) a small patch to support optional fields in 
modules.  This would help achieving the desired effect. See:

http://alain.frisch.fr/info/patch-option-announce
http://alain.frisch.fr/info/patch-option

-- Alain


On 2/5/2014 7:49 PM, Yotam Barnoy wrote:
> Hello List
>
> I would like the following feature, and I'm not enough of an expert in
> module-fu to know if something like this is doable.
>
> Suppose I have a module signature of
>
> module type Monad = sig
>    type 'a m
>    val return : 'a -> 'a m
>    val (>>=) : 'a m -> ('a -> 'b m) -> 'b m
>    val (>>) : 'a m -> 'b m -> 'b m
> end
>
> I would like to have a default implementation for (>>), since a simple
> default implementation is
>
> let (>>) m f = m >>= fun _ -> f
>
> Alternatively, I would like to include this from some DefaultMonad
> module, but have the (>>=) referred to in the function be my newly
> defined (>>=) implementation (ie. late binding). Is there currently any
> way to do this? If not, would there be a way to implement a partial
> default implementation built into or associated with a module signature?
> Something like
>
> module type Monad = sig... default struct... end
>
> Haskell has this available as part of the semantics of their typeclass
> system, and I think it would be really handy to have (if there isn't
> already a way to do it currently).
>
> -Yotam
>
>