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Re: [Caml-list] type var in functor instance?
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Date: 2004-09-20 (15:43)
From: skaller <skaller@u...>
Subject: Re: [Caml-list] type var in functor instance?
On Mon, 2004-09-20 at 21:58, Jean-Christophe Filliatre wrote:
> skaller writes:
>  > Is it possible instantiate a functor with a module
>  > containing a type variable? I have a Set with t = int,
>  > and I now need 'a * int.. 

> Various unsatisfying solutions have been proposed, among which
> - to make a copy of Set with an additional type parameter eveywhere (I
>   attach such a module below. Beware: this is an old version of Set)

Hmmm. I see. I think I understand why this is needed.
Dependent typing problem? Set depends on element...

> - to make an unfunctorized version of Set that uses Pervasives.compare,
>   thus polymorphic

This is already in the standard distro for Hashtbl.
Why not for Set and Map as well? Why is this

I actually use heaps of Hashtbl of polymorphic kind
and am ready to switch some over to an functor instance
with key type int -- most of my tables use int keys
and I hope to gain some performance and reasoning ability.

The duplicate interface has let me experiment rapid
prototyping style, then lock down the typing a bit,
leaving the raw function names and semantics the same.

I think that's nice -- one reason I use Hashtbl
even when Set or Map would be better.

John Skaller, mailto:skaller@users.sf.net
voice: 061-2-9660-0850, 
snail: PO BOX 401 Glebe NSW 2037 Australia
Checkout the Felix programming language http://felix.sf.net

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