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Date: Mon, 9 Jul 2007 11:01:31 +0200
To: Jon Harrop <jon@ffconsultancy.com>
Cc: caml-list@yquem.inria.fr
Subject: Re: [Caml-list] try .. finally using new camlp4
Message-ID: <20070709090131.GA17462@snarc.org>
References: <200707080114.42213.jon@ffconsultancy.com>
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From: tab@snarc.org (Vincent Hanquez)
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X-Spam: no; 0.00; camlp:01 0100,:01 camlp:01 syntax:01 afaict:01 ocaml:01 ocaml:01 compiler:01 expr:01 expr:01 val:01 exn:01 val:01 exn:01 cheers:01 

On Sun, Jul 08, 2007 at 01:14:41AM +0100, Jon Harrop wrote:
> I'm just getting my toe wet with the new camlp4 and I can't get this simple 
> syntax extension to work. AFAICT, the following code:

A bit OT, but I found it quite easy to actually hack ocaml source
directly to do the right thing for try finally. My modification seems to
works correctly, without having any deep knowledge of ocaml internal
compiler code. 

>   EXTEND Gram
>     expr: LEVEL "top"
>     [[ "try"; f=expr; "finally"; g=expr ->
> 	 <:expr<
> 	   ((function
> 	     | `Val v, g -> g(); v
> 	     | `Exn e, g -> g(); raise e)
> 	      ((try `Val($f$) with e -> `Exn e), (fun () -> $g$)))
> 	 >>]];
>   END

I don't know camlp4, but why don't you use a more straightforward
(let r = try f() with e -> g(); raise e in g(); r) construct
instead of wrapping/unwrapping the thing into polymorphic variant ?

Cheers,
-- 
Vincent Hanquez