Hello,

if you want to use recursive modules in the top-level, it seems that you must use the definition form:

        Objective Caml version 3.10.2

# module rec Tmp : sig
    type t = Stop | Next of Tmp.t
  end =
  struct
    type t = Stop | Next of Tmp.t
  end;;
module rec Tmp : sig type t = Stop | Next of Tmp.t end
#

My guess is that the specification is only valid inside a .mli file. And indeed:

modrec.mli:
module rec Tmp : sig type t = Stop | Next of Tmp.t end

"ocamlc -c modrec.mli" works fine,
while
"ocamlc -c modrec.ml" (with modrec.ml having the same contents as modrec.mli) complains it has a syntax error.

Matthieu

----- Message d'origine ----

> De : Jérémie Lumbroso <jeremie.lumbroso@etu.upmc.fr>
> À : caml-list@inria.fr
> Envoyé le : Mercredi, 20 Août 2008, 16h31mn 51s
> Objet : [Caml-list] Specifying recursive modules?
> 
> Hello,
> 
> I'd always thought of separating specification and definition as
> simply not possible in OCaml, but OCaml's reference manual (3.10,
> which is, as far as I can tell, the most recent version of the
> documentation) seems to contradict my assumption:
> 
> http://caml.inria.fr/pub/docs/manual-ocaml/manual021.html#htoc100
> 
> It says that recursive specifications can be written as:
> 
>   
>   module rec : { and ... }
>   
> 
> What does this mean? When I attempt to use this feature in the
> toplevel, it results in an error:
> 
>   
>   # module rec Tmp : sig
>       type t = Stop | Next of Tmp.t
>     end**;;**
>   Syntax error
>   
> 
> On the off-chance that OCaml might explicitly need an "and", I also
> tried adding a second dummy module to the definition, but no dice ...
> When I try to use this feature in a .mli/.ml file coupling, I get the
> same (syntax) error. Have I misunderstood the usage? Or has this been
> removed since its introduction (and the documentation not updated
> accordingly)? Or is this a bug?
> 
> Jérémie
> 
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