Re: [MirageOS-devel] Irmin roadmap

[Thomas Gazagnaire <thomas@xxxxxxxxxxxxxx>]

>> Please feel free to comment if you find something which is not clear or 
>> which could be improved.
> Very quick look. The semantics of timestamps is unspecified:
> 
> http://samoht.github.io/irmin/Irmin.Task.html#VALdate
> 
> Also the uniqueness scope of task uids should be precised.

I think I've addressed these in the freshly updated documentation.

> Besides I see you are using universal values. I don't know if that's useful 
> but you may want to enrich the type a little bit so that you are able to 
> print some diagnostics about them without knowing the client keys. The idea 
> is that client should give a to_string function when they create the key, you 
> can then simply hack a to_string function on universal types using this. 
> There may be more elegant ways but here is one solution (also I would have 
> suggested Formatter, but you may not want to introduce that dependency, see 
> also the types of Task.{create,fprintf} ):
> 
> type univ = { u : exn; str : unit -> string }
> 
> let univ_create (type s) to_string =
>  let module M = struct exception E of s end in
>  (fun v -> { u = M.E v; str = (fun () -> to_string v) }),
>  (function { u = M.E v } -> Some v | _ -> None)
> 
> let to_string u = u.str ()
> 
> Of course the same idea can be applied to other processors you may want on 
> universal values (e.g. marshal).

I've tried to apply that using mirage-tc and I now have:

val create : 'a Tc.t ->  ('a -> t) * (t -> 'a option) * t Tc.t

where a value of type 'a Tc.t can be passed to Tc.show, Tc.of_json, Tc.to_json, 
etc...

Not sure how well it works in practice (I managed to get the top-level throws 
an interesting exception while evaluation Ir_univ.ml with few examples), I'll 
see soon in the backend code.

Thanks,
Thomas
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