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Date: Tue, 26 Nov 2002 12:56:10 +0100
From: Daniel de Rauglaudre <daniel.de_rauglaudre@inria.fr>
To: caml-list@inria.fr
Subject: Re: [Caml-list] camlp4 and let binding...
Message-ID: <20021126125610.D8318@verdot.inria.fr>
References: <20021126042909.GD29607@zed>
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In-Reply-To: <20021126042909.GD29607@zed>; from Pietro.Abate@anu.edu.au on Tue, Nov 26, 2002 at 03:29:09PM +1100
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Hi,

On Tue, Nov 26, 2002 at 03:29:09PM +1100, Pietro Abate wrote:
> 
> I wrote something that, of course, doesn't work. My major problems are about 
> the inner let definitions. How can I chain all let defintions in the list ?

I am not sure I understand what you want to do but this:

>             <str_item:<
>             value $lid:pref$ = $list:definition$ in
>             new rule(pattern,action) 
>             >>

is syntactically incorrect: you must not put "in" after a "value". If
you want to make a let..in inside (like in your example), you have to
make the variable "definition" a list of (patt * expr) and you can
write:

            <str_item:<
            value $lid:pref$ =
              let $list:definition$ in
              new rule(pattern,action)
            >>

If "definition" is, for example, the list: [(p1, e1); (p2; e2)] it is
equivalent to:

            <str_item:<
            value $lid:pref$ =
              let $p1$ = $e1$
              and $p2$ = $e2$ in
              new rule(pattern,action)
            >>

If you prefer a "let..in let.. in" instead of "let .. and .. in", you
have to write it explicitely:

            <str_item:<
            value $lid:pref$ =
              let $p1$ = $e1$ in
              let $p2$ = $e2$ in
              new rule(pattern,action)
            >>

If you want that, but you have a list of let..in with an unknown
number of elements, you have to do it with an iterator, e.g.:

     List.fold_right (fun (p1, e1) e -> <:expr< let $p1$ = $e1$ in $e$ >>)
       list <:expr< new rule(pattern, action) >>

-- 
Daniel de RAUGLAUDRE
http://cristal.inria.fr/~ddr/
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