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[camlp4 extension] pa_refutable : request for comments
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Date: -- (:)
From: blue storm <bluestorm.dylc@g...>
Subject: Re: [Caml-list] [camlp4 extension] pa_refutable : request for comments
On 12/25/07, Nicolas Pouillard <nicolas.pouillard@gmail.com> wrote:
> > There are 6 repetitive lines of code in my refutable_mono function :
> >     let binds_patt binds _loc =
> >       let patt_of_id (id, _loc) = <:patt< $lid:id$ >> in
> >       Ast.PaTup _loc (Ast.paCom_of_list (List.map patt_of_id binds)) in
> >     let binds_expr binds _loc =
> >       let expr_of_id (id, _loc) = <:expr< $lid:id$ >> in
> >       Ast.ExTup _loc (Ast.exCom_of_list (List.map expr_of_id binds)) in
> > Is there an better way to do this ?
>
> In  fact  I  think this part is wrong. What's happen if you get no variable or
> just   one   in  the  pattern?  You  will  try  to  build  a  nil-tuple  or  a
> singleton-tuple and that's forbidden.
>
> Here is the untested code for patterns:
>
> let binds_patt binds _loc =
>   let patt_of_id (id, _loc) = <:patt< $lid:id$ >> in
>   match binds with
>   | [] -> <:patt< () >>
>   | [c] -> patt_of_id c
>   | c :: cs -> <:patt< ( $patt_of_id c$, $list:List.map patt_of_id cs$ ) >>
> in
>
> The  cool  thing is that by making explicit the tuple (by having more than one
> element)  one avoid resorting to concrete constructors and can use the $list:$
> special antiquotation that will insert the paCom_of_list call.

That's right. I fixed (or at least tried to) that in my new version,
http://bluestorm.info/tmp/pa_refutable-0.4.ml.html :

    let binds = (id_folder#patt patt)#get_binds in
    let (binds_patt, binds_expr) =
      let patt_of_id (id, _loc) = <:patt< $lid:id$ >> in
      let expr_of_id (id, _loc) = <:expr< $lid:id$ >> in
      match binds with
      [ [] -> ( <:patt< () >> , <:expr< () >> )
      | [hd] -> ( patt_of_id hd, expr_of_id hd )
      | [hd::tl] ->
         ( <:patt< ( $patt_of_id hd$, $list:List.map patt_of_id tl$ ) >>,
           <:expr< ( $expr_of_id hd$, $list:List.map expr_of_id tl$ ) >> ) ]
    in
    <:binding< $binds_patt$ = match $expr$ with
                  [ $patt$ -> $binds_expr$
                  | _ -> $refutable_err patt$ ] >> ;

> > Lastly, i had to duplicate work in the grammar-modification part,
> > because i didn't manage to use the "opt_rec" rule. I'm not aware of
> > the subtleties of camlp4 parsing; is there another way ?
>
> I don't think there is any subtlety here, just replace:
>
> | "let"; "rec"; "refutable"; bi = binding ->
>     <:str_item< value rec $refutable bi$ >>
> | "let"; "refutable"; bi = binding ->
>     <:str_item< value $refutable bi$ >>
>
> by something like:
>
> | "let"; r = opt_rec; "refutable"; bi = binding ->
>     <:str_item< value $rec:r$ $refutable bi$ >>

Hm. I thought opt_rec wouldn't work, but it looks like i was wrong. I
changed the code to use opt_rec and my test file works flawlessly.

Thanks for your reply