Hiding a public module/type?

Hiding a public module/type?

[David Teller]

     Dear list,

 In order to simplify the error messages for users of my library, I'd
like to hide some type aliasing.

I have the following:

(*** module [Inner], defined in inner.mli ***)
type t


(*** module [Outer], defined in outer.mli ***)
type t = Inner.t
val f : t -> t


Now, module [Inner] is only useful to define the library and shouldn't
be visible from the outside. Unfortunately, for the moment, whenever a
client makes a type error involving [f], the error message looks like

# f 5;;
        ^
This expression has type int but is used with type
 Outer.t = Inner.t

Is there a simple way of turning this error message into

This expression has type int but is used with type
 Outer.t
?


Thanks,
 David

-- 
David Teller-Rajchenbach
 Security of Distributed Systems
  http://www.univ-orleans.fr/lifo/Members/David.Teller
 Angry researcher: French Universities need reforms, but the LRU act
brings liquidations. 

Re: [Caml-list] Hiding a public module/type?

[Martin Jambon]

David Teller wrote:
>      Dear list,
> 
>  In order to simplify the error messages for users of my library, I'd
> like to hide some type aliasing.
> 
> I have the following:
> 
> (*** module [Inner], defined in inner.mli ***)
> type t
> 
> 
> (*** module [Outer], defined in outer.mli ***)
> type t = Inner.t
> val f : t -> t
> 
> 
> Now, module [Inner] is only useful to define the library and shouldn't
> be visible from the outside. Unfortunately, for the moment, whenever a
> client makes a type error involving [f], the error message looks like
> 
> # f 5;;
>         ^
> This expression has type int but is used with type
>  Outer.t = Inner.t
> 
> Is there a simple way of turning this error message into
> 
> This expression has type int but is used with type
>  Outer.t
> ?

One solution consists in using submodules for achieving an intermediate
level of privacy ("friend" modules):

$ cat inner.mli
type t = int

$ cat outer.mli
type t = Inner.t
val f : t -> t

$ cat packed.mli
module Outer :
sig
  type t
  val f : t -> t
end


Create valid inner.ml and outer.ml files but no packed.ml.

Compile:

$ ocamlc -c inner.mli
$ ocamlc -c outer.mli
$ ocamlc -c inner.ml
$ ocamlc -c outer.ml

Pack:

$ ocamlc -c packed.mli
$ ocamlc -pack -o packed.cmo inner.cmo outer.cmo


Then you only have to install the packed.cm* files. It gives you:

# Packed.Outer.f 5;;
This expression has type int but is here used with type Packed.Outer.t



Martin
-- 
http://mjambon.com/

Re: [Caml-list] Hiding a public module/type?

[David Teller]

Thanks, I'll try that.


On Tue, 2008-11-04 at 00:38 +0100, Martin Jambon wrote:
> Then you only have to install the packed.cm* files. It gives you:
> 
> # Packed.Outer.f 5;;
> This expression has type int but is here used with type Packed.Outer.t
> 
> 
> 
> Martin
-- 
David Teller-Rajchenbach
 Security of Distributed Systems
  http://www.univ-orleans.fr/lifo/Members/David.Teller
 Angry researcher: French Universities need reforms, but the LRU act
brings liquidations.