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Date: Tue, 20 Jan 2009 08:33:53 -0800 (PST)
From: Dario Teixeira <darioteixeira@yahoo.com>
Subject: Re: [Caml-list] Private types in 3.11, again
To: caml-list@yquem.inria.fr
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X-Spam: no; 0.00; variants:01 variants:01 node:01 annotations:01 coercions:01 node:01 sig:01 val:01 val:01 struct:01 seq:01 seq:01 printf:01 sprintf:01 printf:01 

Hi again,

I ditched the regular variants in favour of polymorphic variants, hoping
the coercion trick described by Jacques Garrigue would help [1].  I've also
simplified the formulation as much as possible.  Anyway, I'm still stuck
with the same problem: while function 'sprint' works alright inside the
Node module, its clone 'sprint2' fails to compile when placed outside.
Is this a case where no amount of explicit annotations and coercions will
work or am I missing something obvious?

Thanks in advance!
Regards,
Dario Teixeira

[1] http://groups.google.com/group/fa.caml/msg/855011402f1ca1b5


module Node:
sig
=09type elem_t =3D [ `Text of string | `Bold of elem_t list ]
=09type +'a t =3D private elem_t

=09val text: string -> [> `Basic ] t
=09val bold: 'a t list -> [> `Complex ] t
=09val sprint: 'a t -> string
end =3D
struct
=09type elem_t =3D [ `Text of string | `Bold of elem_t list ]
=09type +'a t =3D elem_t

=09let text str =3D `Text str
=09let bold seq =3D `Bold seq
=09let rec sprint =3D function
=09=09| `Text str=09-> Printf.sprintf "(Text %s)" str
=09=09| `Bold seq=09-> Printf.sprintf "(Bold %s)" (List.fold_left (^) "" (L=
ist.map sprint seq))
end


module Foobar:
sig
=09val sprint2: 'a Node.t -> string
end =3D
struct
=09let rec sprint2 node =3D match (node : _ Node.t :> [> ]) with
=09=09| `Text str=09-> Printf.sprintf "(Text %s)" str
=09=09| `Bold seq=09-> Printf.sprintf "(Bold %s)" (List.fold_left (^) "" (L=
ist.map sprint2 (seq : _ Node.t list :> [>] list)))
end
=0A=0A=0A