Re: [Caml-list] Heterogeneous dictionary

[David House <dhouse@janestreet.com>]

I don't quite understand the problem. Here's an example of how one
might use univ_map:

open Core.Std

module Keys : sig
  val recovery : int Univ_map.Key.t
  val resist_pain : float  Univ_map.Key.t
end = struct
  let recovery = Univ_key.Key.create "recovery" Int.sexp_of_t
  let resist_pain = Univ_key.Key.create "resist_pain" Float.sexp_of_t
end

(In practice this might be two files: keys.ml with the implementation
and keys.mli with the signature.) You can then add things as follows:

let add map ~key ~data = Univ_map.add_exn map key data in
let map =
  Univ_map.empty
  |> add ~key:Keys.recovery ~data:4
  |> add ~key:Keys.resist_pain ~data:10.
in
...

On 4 April 2013 09:37, Anthony Tavener <anthony.tavener@gmail.com> wrote:
> Thank-you for the advice and pointers, folks...
>
> Well, the common problem is still the same one I've been struggling with:
> "creating keys", and having to access them.
>
> I can't create keys "type-free" in a common module. As I figured... having
> "modifier.ml" with a bunch of Key.create will have monomorphic types which
> can't be resolved since with no usage in that module to make the type
> concrete. I had a nagging feeling I'd need a "whole-program" compiler...
>
> Instead I'd have to create keys in modules where they are used... but then I
> might have a mess of keys like Wounds.recovery, Combat.resist_pain, ... the
> problem being that only a fraction of these keys actually make sense being
> associated to a particular module, and it gets confusing to know which (of
> several candidates) I decided to stash them into. This was the attraction to
> polymorphic variants (which I rarely use) -- they give a pre-ordained unique
> ID based on a simple name... no declaration, and no module prefixing, which
> seems important to me for this case.
>
> Note that I have a "database" of tables with different types (implemented by
> first-class modules!), and it works great for the bulk of my game-state, but
> each table is well-populated and heavily used in consistent manner. These
> modifiers though... they're a bit like ad-hoc message passing, where I can
> submit any message and anywhere else add a snippet of code to interpret it
> (not that I have any of that going on, otherwise it might hold the
> solution!).
>
>
>
> On Thu, Apr 4, 2013 at 1:38 AM, Raphaël Proust <raphlalou@gmail.com> wrote:
>>
>> On Thu, Apr 4, 2013 at 1:45 AM, Anthony Tavener
>> <anthony.tavener@gmail.com> wrote:
>> > […]
>>
>> And yet-another-solution, Ocsigen's Polytable:
>> http://ocsigen.org/ocsigenserver/api/Polytables
>>
>>
>> Cheers,
>> --
>> ______________
>> Raphaël Proust
>
>