Re: [Caml-list] camlp4 3.10: Matching variant types

["Dmitry Bely" <dmitry.bely@gmail.com>]

Probably the following is related to Joel's questions on variant type
matching. I am trying to convert IoXML syntax extension to the new
camlp4. Currently I am stuck here:

...
value gen_output_cons (loc, c, tl) =
  let p =
    let p = <:patt< $uid:c$ >> in
    let (p, _) =
      List.fold_left
        (fun (p, cnt) _ ->
           let p = <:patt< $p$ $lid:pname cnt$ >> in
           (p, cnt + 1))
        (p, 1) tl
    in
    p
  in
  let e = gen_xprint_cons loc c tl in
  (p, None, e)
;
...
value gen_output_sum loc cdl =
  let mc =
    List.fold_right
      (fun cd mc ->
        let (p, _, e) = gen_output_cons cd in
          <:match_case< $p$ -> $e$ | $mc$ >>)
	  cdl <:match_case<>> in
  <:expr< fun ppf -> fun [ $mc$ ] >>
;
...
value gen_output_funs loc tdl sil =
  let pel =
    List.fold_right
      (fun ((loc, n), tpl, tk, cl) pel ->
         let body =
           loop tk where rec loop =
             fun
             [ <:ctyp< [ $cdl$ ] >> -> gen_output_sum loc cdl

File "pa_ioXML.ml", line 257, characters 58-61:
This expression has type Camlp4.PreCast.Ast.ctyp but is here used with type
  (Camlp4.PreCast.Ast.Loc.t * string * Camlp4.PreCast.Ast.ctyp list) list

As usual: (cdl) was a list before, now it is not. Is were a simple way
to get a list and make (gen_output_sum) happy? Or this should be
complete rewritten - how?

- Dmitry Bely