Wait, sorry again, I figured out the correct type:

  let lbl_expr_list = 
    (Obj.magic (Grammar.Entry.find expr "lbl_expr_list") :
       (MLast.patt * MLast.expr) list Grammar.Entry.e) in

as you said, then "car" the first list element and it's right:

    [ [ $cons$; "{"; memb = LIST1 lbl_expr_list SEP ";" ; "}" -> 
          (let memb0= List.nth memb 0 in
          <:expr<{$list:memb0$}>>) ] ]

I don't understand it though.  Is there some explanation?


Jeff



> -----Original Message-----
> From: owner-caml-list@pauillac.inria.fr
> [mailto:owner-caml-list@pauillac.inria.fr]On Behalf Of Jeff Henrikson
> Sent: Sunday, January 13, 2002 9:18 PM
> To: Daniel de Rauglaudre
> Cc: caml-list@inria.fr
> Subject: RE: [Caml-list] camlp4: LIST1 construct on record patterns
> 
> 
> I actually tried magicing it into what I wanted it to be before, but was unable to guess it's real type.  Apparently I 
> still can't:
> 
> 
> open Printf;;
> 
> let try_extend _ =
>   let cons = "Bogus" in
>   let lbl_expr_list =
>     (Obj.magic (Grammar.Entry.find expr "lbl_expr_list") :
>        (MLast.patt * MLast.expr) (* not list *) Grammar.Entry.e) in
>   EXTEND
>     expr: LEVEL "simple"
>     [ [ $cons$; "{"; memb = LIST1 lbl_expr_list SEP ";" ; "}" ->
>           <:expr<{$list:memb$}>> ] ]
>     ;
>   END;;
> 
> try_extend 7;;
> 
> Bogus{foo="happy";bar="sad"};;
> 
> 
> This segfaults.  Let's see if memb is even a list:
> 
> 
> let try_extend _ =
>   let cons = "Bogus" in
>   let lbl_expr_list =
>     (Obj.magic (Grammar.Entry.find expr "lbl_expr_list") :
>        (MLast.patt * MLast.expr) (* not list *) Grammar.Entry.e) in
>   EXTEND
>     expr: LEVEL "simple"
>     [ [ $cons$; "{"; memb = LIST1 lbl_expr_list SEP ";" ; "}" ->
>           (printf "Do we get here %d\n" (List.length memb); flush stdout;
>           <:expr<6>>) ] ]
>     ;
>   END;;
> 
> try_extend 7;;
> 
> Bogus{foo="happy";bar="sad"};;
> 
> 
> This prints "Do we get here 1", regardless of how many terms I add in Bogus{}, regardless of whether such constructors 
> are defined
> or not.
> 
> But despite all this the source code looks convincing enough:
> 
> pa_o.ml:
>       | "{"; test_label_eq; lel = lbl_expr_list; "}" ->
>           <:expr< { $list:lel$ } >>
> 
> > Sorry, Luke, you entered the dark side of Camlp4... :-)
> 
> Apparently the force is not strong enough within me.  ;-}
> 
> 
> Jeff
> 
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