From: Jacques Garrigue <garrigue@kurims.kyoto-u.ac.jp>
To: pixel@mandrakesoft.com
Cc: caml-list@inria.fr
Subject: Re: [Caml-list] Is a Cow an Animal?
Date: Thu, 18 Apr 2002 21:52:32 +0900 [thread overview]
Message-ID: <20020418215232T.garrigue@kurims.kyoto-u.ac.jp> (raw)
In-Reply-To: <lyads1p5s6.fsf@leia.mandrakesoft.com>
From: Pixel <pixel@mandrakesoft.com>
> * one pb was:
>
> let is_meat_ = function
> | `Beef | `Dead_rabbit | `Dead_human -> true
> | _ -> false
>
> which type "[> `Beef | `Dead_rabbit | `Dead_human] -> bool" doesn't allow
> is_meat_ (food : [`Grass])
This is to avoid _too_ weak typings, which would allow for bad typos.
The more direct solution is
let is_meat_ = function
| #meat_kind -> true
| #vegetable_kind -> false
> * I still can't manage to have:
>
> new_human : int -> ([ `Dead_human], [< food_kind]) animal
> all i got is
> new_human : int -> ([ `Dead_human], _[< food_kind]) animal
Classical solution is eta-expansion
let new_human n : ([`Dead_human], [< food_kind ]) animal =
new animal `Human `Dead_human n
should work.
Basically, for closed world problems polymorphic variants work
generally better than object encodings. If you want it open world,
this gets more subtle.
Jacques Garrigue
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next prev parent reply other threads:[~2002-04-18 12:53 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-04-17 23:40 Pixel
2002-04-18 2:17 ` John Max Skaller
2002-04-18 10:19 ` Pixel
2002-04-18 12:09 ` Pixel
2002-04-18 12:52 ` Jacques Garrigue [this message]
2002-04-18 13:03 ` Pixel
2002-04-18 18:58 ` james woodyatt
2002-04-18 22:44 ` Pixel
2002-04-18 22:57 ` james woodyatt
2002-04-18 23:31 ` Pixel
2002-04-19 0:21 ` Remi VANICAT
2002-04-19 0:51 ` james woodyatt
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