Here's a (very) quick and dirty implementation that will automatically populate
data, using our dynamic typing library ( http://github.com/mirage/dyntype ).
You just need to fill in desc_of_license with the matching descriptions, and
data will be auto-populated at program startup.
-anil
--
type license = GPL | LGPL with type_of,value
(* For a type, generate a description string *)
let desc_of_license = function
|"GPL",_ -> "GNU General Public License"
|"LGPL",_ -> "GNU Lesser GPL"
|_ -> failwith "unknown license"
(* Generate a list of license types *)
let licenses = match type_of_license with
| Type.Ext ("license", Type.Sum ts) -> ts
| _ -> assert false
(* From a license type, generate a Value of that type *)
let value_of_license_t = function
|name,[] -> Value.Ext (("",0L), Value.Sum (name,[]))
|name,_ -> failwith "no args allowed"
(* Populate data with licenses and their description *)
let data = List.map
(fun lic ->
(license_of_value (value_of_license_t lic)) ,
(desc_of_license lic)
) licenses
let _ =
Printf.printf "GPL: %s\n%!" (List.assoc GPL data);
Printf.printf "LGPL: %s\n%!" (List.assoc LGPL data)
--
-anil
On 3 Sep 2010, at 18:16, Sylvain Le Gall wrote:
> Hello all,
>
> I would like to somehow enforce that a variant type is associated with
> an entry in a data list.
>
> For example,
>
> I would like to define:
>
> type license = GPL | LGPL
>
> and
>
> let data = [ GPL, "GNU Public license";
> LGPL, "GNU Lesser General Public license" ]
>
>
> I would like to enforce that all variants of license are in the
> association list.
>
> I have tried to use polymorphic variants, but don't see how to enforce
> this constraint.
>
> The point, is that if I add a new variant to license (e.g. BSD3), the
> compiler output an error because this new variant is not in data list.
>
> Any ideas ? If you need to use another type expression rather than
> variant, please do so, as long as I am able to link the license type
> and data list.
>
> Thanks all,
> Sylvain Le Gall
>
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