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Message-ID: <45AA74B0.3070309@gmail.com>
Date: Sun, 14 Jan 2007 12:21:36 -0600
From: Edgar Friendly <thelema314@gmail.com>
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To: ketty <kattlachan@gmail.com>
Cc: caml-list@yquem.inria.fr
Subject: Re: [Caml-list] Ocaml compiler features
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X-Spam: no; 0.00; ocaml:01 compiler:01 arrays:01 type-safe:01 printf:01 hashtbl:01 syntax:01 hashtables:01 hashtbl:01 variants:01 edgar:98 ketty:98 edgar:98 zack:01 wrote:01 

ketty wrote:
> On 1/14/07, Edgar Friendly <thelema314@gmail.com> wrote:
>> That gives me what I've asked for at the moment, but I really want
>> arrays indexed by atomic variant types in a type-safe way.  i.e. so I
>> could do:
>>
>> type food = Carrot | Apple | Pizza | Coke | Sushi
>> let in_supply = Super_array.create food 0
>> in_supply.(Coke) <- 20
>> for f in food'range do
>>         printf "%s - %d" f'name in_supply.(f)
>> done
>>
> 
> What you really want is a mapping from a variant type to elements of
> data. We already have the Map and Hashtbl modules for that. Although
> it would be nice with some syntactic sugar for dealing with them.
> There seems to be an old syntax extension for hashtables here:
> http://www.bononia.it/~zack/stuff/hashtbl_ext.ml
> 
Yes to the first sentence, I think no on the second.  Map and Hashtbl
are very good, but I think I really want an array.  For an ('a, 'b) Map,
this is for situations where the set of 'a is fixed at design time, I
don't see the overhead of Maps and Hashtbls being appropriate.  Atomic
variants already have unique ids from 0 to n-1, so they seem quite
appropriate for this kind of task.

E.