From mboxrd@z Thu Jan  1 00:00:00 1970
Received: (from weis@localhost) by pauillac.inria.fr (8.7.6/8.7.3) id KAA07277 for caml-red; Tue, 22 Aug 2000 10:34:51 +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 KAA11504 for <caml-list@pauillac.inria.fr>; Tue, 22 Aug 2000 10:31:33 +0200 (MET DST)
Received: from pauillac.inria.fr (pauillac.inria.fr [128.93.11.35])
	by concorde.inria.fr (8.10.0/8.10.0) with ESMTP id e7M8VST06038;
	Tue, 22 Aug 2000 10:31:28 +0200 (MET DST)
Received: (from weis@localhost) by pauillac.inria.fr (8.7.6/8.7.3) id KAA10895; Tue, 22 Aug 2000 10:31:27 +0200 (MET DST)
From: Pierre Weis <Pierre.Weis@inria.fr>
Message-Id: <200008220831.KAA10895@pauillac.inria.fr>
Subject: Re: Question on language design (keywords vs Pervasives)
In-Reply-To: <200008220038.JAA10162@ropas.kaist.ac.kr> from Kwangkeun Yi at "Aug 22, 100 09:38:05 am"
To: kwang@ropas.kaist.ac.kr (Kwangkeun Yi)
Date: Tue, 22 Aug 2000 10:31:27 +0200 (MET DST)
Cc: caml-list@inria.fr
X-Mailer: ELM [version 2.4ME+ PL28 (25)]
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Sender: weis@pauillac.inria.fr

> > I'm sure that there is no ``more primitive function'' than raise to
> > raise an exception. So sorry, you cannot define raise ``in terms of a
> > more primitive function'' in Caml. You would need a language with
> > call/cc to express that, and Caml is not this language.
> 
> To make it precise, we don't even need call/cc. 
> Just a kind of cps transformation that carries two continuations (one
> for normal continuation and the other for handler continuation)
> removes all the raise/try expressions. The transformation is
> well-known. See 
> 
> @InProceedings{KiYiDa98,
>   author =       "Jung-taek Kim and Kwangkeun Yi and Olivier Danvy",
>   title =        "Assessing the Overhead of ML Exceptions by Selective
>                   CPS Transformation",
>   pages =     "103-114",
>   booktitle = "The Proceedings of the ACM SIGPLAN Workshop on ML",
>   year =      1998,
>   url = "http://ropas.kaist.ac.kr/~kwang/paper/98-ml-kiyida.ps.gz",
>   month =     sep
> }
> 
> -Kwang
> 
> --
> Kwangkeun Yi		http://cs.kaist.ac.kr/~kwang

The problem was not to remove try/raise expressions from programs, but
to define raise in terms of ``more primitive functions''. I'm not sure
a cps transformation can be considered as ``a primitive function'' of
the language that can help to define raise into the language.

I'm sure you can use a lot of other transformations to remove
try/raise, e.g. a monadic transformation or a direct expression of the
semantics of exceptions (using a direct sum of normal and exceptional
results) could also do the job.

Pierre Weis

INRIA, Projet Cristal, Pierre.Weis@inria.fr, http://cristal.inria.fr/~weis/