From mboxrd@z Thu Jan  1 00:00:00 1970
Received: (from majordomo@localhost) by pauillac.inria.fr (8.7.6/8.7.3) id JAA29843; Tue, 19 Jun 2001 09:12:54 +0200 (MET DST)
X-Authentication-Warning: pauillac.inria.fr: majordomo set sender to owner-caml-list@pauillac.inria.fr using -f
Received: (from weis@localhost) by pauillac.inria.fr (8.7.6/8.7.3) id JAA30708 for caml-list@pauillac.inria.fr; Tue, 19 Jun 2001 09:12:53 +0200 (MET DST)
Received: from concorde.inria.fr (concorde.inria.fr [192.93.2.39]) by pauillac.inria.fr (8.7.6/8.7.3) with ESMTP id OAA18441 for <caml-list@pauillac.inria.fr>; Mon, 18 Jun 2001 14:13:13 +0200 (MET DST)
Received: from morgon.inria.fr (morgon.inria.fr [128.93.8.33])
	by concorde.inria.fr (8.11.1/8.10.0) with ESMTP id f5ICCen05599;
	Mon, 18 Jun 2001 14:12:40 +0200 (MET DST)
Received: (from remy@localhost)
	by morgon.inria.fr (8.9.3/8.9.3) id OAA31058;
	Mon, 18 Jun 2001 14:15:22 +0200
To: Tyng-Ruey Chuang <trc@iis.sinica.edu.tw>
Cc: caml-list@inria.fr,
        Jean-Christophe.Filliatre@lri.fr (Jean-Christophe Filliatre)
Subject: Re: [Caml-list] Weird types
References: <200106180804.QAA18021@iota.iis.sinica.edu.tw>
From: Didier Remy <remy@morgon.inria.fr>
Date: 18 Jun 2001 14:15:21 +0200
In-Reply-To: Tyng-Ruey Chuang's message of "Mon, 18 Jun 2001 16:04:32 +0800 (CST)"
Message-ID: <m38d782t25i.fsf@morgon.inria.fr>
X-Mailer: Gnus v5.7/Emacs 20.4
Sender: owner-caml-list@pauillac.inria.fr
Precedence: bulk

Tyng-Ruey Chuang <trc@iis.sinica.edu.tw> writes:

> Jean-Christophe FILLIATRE wrote:
> > Actually, there  is a  type-able way of  writing this  function, which
> > consists in duplicating it into two functions, like this:
> > 
> > ======================================================================
> > type ('a,'b,'c) t =
> >   | A of 'a * 'b * 'c
> >   | B of ('b, 'a, 'c) t
> > 
> > let rec gamma = function
> >   | A _ -> 0
> >   | B x -> 1 + gamma' x
> > 
> > and gamma' = function
> >   | A _ -> 0
> >   | B x -> 1 + gamma x
> > ======================================================================
> > 
> > which gives the expected types:
> > 
> > ======================================================================
> > val gamma : ('a, 'b, 'c) t -> int = <fun>
> > val gamma' : ('a, 'b, 'c) t -> int = <fun>
> > ======================================================================
> 
> Interesting! But then size of the duplicated code grows exponentially.

Actually, you can share a little more: 

        let gamma_body gamma = function 
           | A _ -> 0
           | B x -> 1 + gamma x

        let rec gamma  x = gamma_body gamma' x 
            and gamma' x = gamma_body gamma  x;;
        ;;

and a for three parameters: 

        type ('a, 'b, 'c) sigma = 
          | I of 'a * 'b * 'c 
          | T of ('b, 'a, 'c) sigma
          | P of ('b, 'c, 'a) sigma

        let body gT gP = function
           | I _ -> 0
           | T x -> 1 + gT x
           | P x -> 1 + gP x

        let rec abc s = body bac bca s
            and acb s = body cab cba s
            and bac s = body abc acb s
            and bca s = body cba cab s
            and cab s = body acb abc s
            and cba s = body bca bac s
        ;;

Didier
-------------------
Bug reports: http://caml.inria.fr/bin/caml-bugs  FAQ: http://caml.inria.fr/FAQ/
To unsubscribe, mail caml-list-request@inria.fr  Archives: http://caml.inria.fr