A signature that cannot be inhabited by any structures

A signature that cannot be inhabited by any structures

[Hyeonseung Im]

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Hi all.

 

I found something interesting. In the OCaml, the following signature is
valid. (I tested it with the OCaml version 3.09.2 and 3.10.0.)

 

(In the top-level)

# module type S = sig val x : int val x : float end;;

module type S = sig val x : int val x : float end

 

But, this module type seems not to be inhabited by any structures. On the
contrary, in the SML this sort of module types cannot be defined. (Actually,
it raises an error: the duplication of variables.)

 

I wonder if this is a feature of the OCaml (or maybe a bug in the
implementation).

I'd appreciate any comment on it.

 

Hyeonseung Im.

 


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Re: [Caml-list] A signature that cannot be inhabited by any structures

[Vincent Aravantinos]

Le 8 sept. 07 à 09:54, Hyeonseung Im a écrit :

> Hi all.
>
>
>
> I found something interesting. In the OCaml, the following  
> signature is valid. (I tested it with the OCaml version 3.09.2 and  
> 3.10.0.)
>
>
>
> (In the top-level)
>
> # module type S = sig val x : int val x : float end;;
>
> module type S = sig val x : int val x : float end
>
>
>
> But, this module type seems not to be inhabited by any structures.  
> On the contrary, in the SML this sort of module types cannot be  
> defined. (Actually, it raises an error: the duplication of variables.)
>
>
>
> I wonder if this is a feature of the OCaml (or maybe a bug in the  
> implementation).
>
> I’d appreciate any comment on it.
>
>
>
> Hyeonseung Im.
>

Hi,

apart from the question "is this a bug or a feature ?", I'd like to  
say this is quite useful when you want to do some kind of inheritance  
between modules.
See http://caml.inria.fr/pub/ml-archives/caml-list/ 
2007/08/8f1e17b89b64d66ae406521947709aff.en.html for the different  
situation for type replication.

Vincent