Re: [Caml-list] One-value functors

[Nicolas Braud-Santoni <nicolas@braud-santoni.eu>]

Hi,

If I'm not mistaken, you want something like Haskell's typeclasses.
I agree that it's a feature I often find myself wanting in OCaml, and
-as you point out- is trivial to encode with module and functors, so
it shouldn't be highly problematic.

Is there some syntax extension providing such a feature ?
If not, are there plans to have syntax for typeclass-like functor operations ?

Regard,
Nicolas

2012/5/11 Arnaud Spiwack <Arnaud.Spiwack@lix.polytechnique.fr>:
> Dear all,
>
> With the advent of first-class modules, I find myself more and more wanting
> to write functors with only one (value) component, just to benefit from type
> dependencies.
>[...]
>
> We could have the type
>> (X:A) => t
>
> stand for (something like)
>> module F = functor (X:A) -> sig val x : t end
>> (module F)
>
> and the definition
>> let f {{X:A}} = e
>
> stand for
>> let f = let module F (X:A) -> struct let x = e end
>
> and finally we'd need an application
>> e {{M}}
>
> would stand for (something like)
>> let module F = (val e) in let module F' = F(M) in F'.x
>
> Clearly the application needs something like OCaml 4.0 and the type
> definition some kind of cleverness (I don't know, by the way, why the syntax
> for F cannot be inlined in the type).
> [...]