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Message-ID: <47166E74.40306@frisch.fr>
Date: Wed, 17 Oct 2007 22:20:04 +0200
From: Alain Frisch <alain@frisch.fr>
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To: Dario Teixeira <darioteixeira@yahoo.com>
Cc: Francisco Jos? Valverde Albacete <fva@tsc.uc3m.es>,
	caml-list@yquem.inria.fr
Subject: Re: [Caml-list] Smells like duck-typing
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X-Spam: no; 0.00; frisch:01 frisch:01 cduce:01 ocamlduce:01 ocamlduce:01 fwiw:01 intersection:01 printf:01 printf:01 wrote:01 caml-list:01 int:01 int:01 alain:01 alain:01 

Dario Teixeira wrote:
>> To me your problems looks like a good candidate for XML-modelling and 
>> reusing all the tools for working in XML. The more so because XML was 
>> made... exactly for that! Why don't  you give it at least a somewhat 
>> serious thought?
> 
> Hi,
> 
> You mean like CDuce and/or OCamlduce?

I'm not particularly encouraging the use of OCamlduce here, but FWIW, a 
solution would look like:

type title = {{ { title=Latin1 ..} }}
type intro = {{ { intro=Latin1 ..} }}
type blurb_t = {{ { id=Int .. } ++ title ++ intro }}
type fresh_t = {{ { body=Latin1 .. } ++ title ++ intro }}
type full_t = {{ blurb_t & fresh_t }}   (* intersection type *)

let print_metadata s =
   Printf.printf "%d: %s\n" {:s.id:} {:s.title:}

If you're ok duplicating fields, the type definitions can be simplified:

type blurb_t = {{ {id=Int title=Latin1 intro=Latin1 ..} }}
type fresh_t = {{ {body=Latin1 title=Latin1 intro=Latin1 ..} }}
type full_t = {{ {id=Int body=Latin1 title=Latin1 intro=Latin1 ..} }}


-- Alain