[Caml-list] Section 7.14: First-class modules

[Caml-list] Section 7.14: First-class modules

[Matej Kosik]

Hello,

In Section 7.14 of the Ocaml manual:

http://caml.inria.fr/pub/docs/manual-ocaml/manual021.html#toc81

there is a `Basic example'.

The code (with some essential fillings) may look like this:

--------------------------------------------------
  module type DEVICE = sig type t
                           val foo : unit -> unit
                       end
  let devices : (string, module DEVICE) Hashtbl.t = Hashtbl.create 17

  module SVG = struct
                 type t = int
                 let foo _ = assert false
               end

  let _ = Hashtbl.add devices "SVG" (module SVG : DEVICE)

  module PDF = struct
                 type t = float
                 let foo _ = assert false
               end

  let _ = Hashtbl.add devices "PDF" (module PDF: DEVICE)

  module Device =
      (val (try Hashtbl.find devices (parse_cmdline())
            with Not_found -> eprintf "Unknown device %s\n"; exit 2)
       : DEVICE
      )
---------------------------------------------------

When I try to compile this piece of code:

    ocamlc -o main main.ml

I get an error:

   File "main.ml", line 4, characters 23-29:
   Error: Syntax error
   make: *** [main] Error 2

Is that example sound (for Ocaml 3.12)?
Or did I spoiled something myself?
I would be grateful for any advice. Thank you in advance.

The compiler does not seem to like giving `module DEVICE' as the second
parameter to the Hashtbl.t type constructor. I am not actually sure what
`module DEVICE' could, semantically, mean.

Re: [Caml-list] Section 7.14: First-class modules

[Esther Baruk]

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Hi,

the type expression must be put between parenthesis. I think it is an error
in the manual.

The following works : (string, (module DEVICE)) Hashtbl.t


Esther Baruk


On Tue, Aug 14, 2012 at 5:11 PM, Matej Kosik <
5764c029b688c1c0d24a2e97cd764f@gmail.com> wrote:

> Hello,
>
> In Section 7.14 of the Ocaml manual:
>
> http://caml.inria.fr/pub/docs/manual-ocaml/manual021.html#toc81
>
> there is a `Basic example'.
>
> The code (with some essential fillings) may look like this:
>
> --------------------------------------------------
>   module type DEVICE = sig type t
>                            val foo : unit -> unit
>                        end
>   let devices : (string, module DEVICE) Hashtbl.t = Hashtbl.create 17
>
>   module SVG = struct
>                  type t = int
>                  let foo _ = assert false
>                end
>
>   let _ = Hashtbl.add devices "SVG" (module SVG : DEVICE)
>
>   module PDF = struct
>                  type t = float
>                  let foo _ = assert false
>                end
>
>   let _ = Hashtbl.add devices "PDF" (module PDF: DEVICE)
>
>   module Device =
>       (val (try Hashtbl.find devices (parse_cmdline())
>             with Not_found -> eprintf "Unknown device %s\n"; exit 2)
>        : DEVICE
>       )
> ---------------------------------------------------
>
> When I try to compile this piece of code:
>
>     ocamlc -o main main.ml
>
> I get an error:
>
>    File "main.ml", line 4, characters 23-29:
>    Error: Syntax error
>    make: *** [main] Error 2
>
> Is that example sound (for Ocaml 3.12)?
> Or did I spoiled something myself?
> I would be grateful for any advice. Thank you in advance.
>
> The compiler does not seem to like giving `module DEVICE' as the second
> parameter to the Hashtbl.t type constructor. I am not actually sure what
> `module DEVICE' could, semantically, mean.
>
> --
> Caml-list mailing list.  Subscription management and archives:
> https://sympa-roc.inria.fr/wws/info/caml-list
> Beginner's list: http://groups.yahoo.com/group/ocaml_beginners
> Bug reports: http://caml.inria.fr/bin/caml-bugs
>
>

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Re: [Caml-list] Section 7.14: First-class modules

[Matej Kosik]

On 14/08/12 16:28, Esther Baruk wrote:
> Hi,
> 
> the type expression must be put between parenthesis. I think it is an
> error in the manual.
> 
> The following works : (string, (module DEVICE)) Hashtbl.t

I have filed a bugreport concerning the documentation.

Besides missing parentheses, there were no other problems. I never
needed this feature before but the refactoring I made today would be
impossible without it.

Thanks again :-)