From: Sylvain Le Gall <sylvain@le-gall.net>
To: caml-list@inria.fr
Subject: Re: Type constraint to explain that a polymorphic variants is included into another
Date: Mon, 11 Oct 2010 08:49:51 +0000 (UTC) [thread overview]
Message-ID: <slrnib5jte.fmh.sylvain@gallu.homelinux.org> (raw)
In-Reply-To: <CE9DC29C-F580-4703-9C6C-87CEF7994455@gmail.com>
Hello,
On 08-10-2010, Jacques Garrigue <garrigue@math.nagoya-u.ac.jp> wrote:
> On 2010/10/09, at 2:13, Sylvain Le Gall wrote:
>
>> Hello all,
>>
>> I would like to build an interface for plugins that allow to extract at the
>> same time a very specific data for a plugin family and to extract
>> general help for plugins.
>>
>> Here is an example:
>
> [...]
>
>> This code doesn't compile because I see no way to explain that F.kind is
>> included into plugin_kind.
>
> I'm not sure of what you are trying to do, but private rows where introduced
> with this goal in mind.
>
> The idea is to change the abstract definition of kind in PLUGIN_FAMILY to
>
> type kind = private [< plugin_kind]
>
> meaning that kind can be instantiated to any subset of plugin_kind.
> You can then use subtyping to convert from kind to plugin_kind.
>
Very nice OCaml extension. It indeed solves my problem. I was aware of private
type, but don't yet know how to use it.
> Here is a typable version of your code.
>
> let run pkg =
> prerr_endline (help (pkg.plugin_build :> MapPlugin.key));
> prerr_endline (help (pkg.plugin_install :> MapPlugin.key));
> (Build.act pkg.plugin_build) ();
> Install.act pkg.plugin_install []
>
That is perfect. If I add the following call, with your solution:
(Install.act pkg.plugin_build) []
I get this error:
ocamlc -o test test.ml
File "test.ml", line 84, characters 14-30:
Error: This expression has type [ `Build ] plugin = [ `Build ] * string
but an expression was expected of type
[ `Install ] plugin = [ `Install ] * string
These two variant types have no intersection
make: *** [all] Erreur 2
This is exactly what I want.
Thanks,
Sylvain Le Gall
prev parent reply other threads:[~2010-10-11 8:50 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-10-08 17:13 Sylvain Le Gall
2010-10-08 18:13 ` [Caml-list] " Jake Donham
2010-10-08 22:10 ` Sylvain Le Gall
2010-10-08 20:09 ` [Caml-list] " Jacques Garrigue
2010-10-11 8:49 ` Sylvain Le Gall [this message]
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