Private type syntax and error message

Private type syntax and error message

[Colonna Francois]

Hello,

if, as I found in the documentation, I write :
 
# type my_int = private int;;

I get the message : "This fixed type is not an object or variant"

1. The message is very obscure
2. why this syntax is not implemented as it should be ?

Best,

François Colonna

Re: [Caml-list] Private type syntax and error message

[Dario Teixeira]

> What do you expect it to do that might work? If it created
> an abstract type 
> the type would be useless, having no way to construct or
> destructure values 
> of that type...

Hi,

I think the idea is that the type would be declared inside
a module that would provide constructor functions.  Moreover,
because private is not abstract, it would allow the outside
world to pattern-match on values of that type.  This is actually
a very useful feature.

Btw, the code works on 3.11 CVS!

Cheers,
Dario Teixeira

Re: [Caml-list] Private type syntax and error message

[Virgile Prevosto]

Hello,

Le ven 12 sep 2008 07:19:54 CEST,
Dario Teixeira <darioteixeira@yahoo.com> a écrit :

> 
> Btw, the code works on 3.11 CVS!
> 
Yes, this is a feature scheduled to be added in 3.11. in 3.10.x, only
variant and records can be made private. 

Le ven 12 sep 2008 15:43:19 CEST,
Colonna Francois <f.colonnacesari@free.fr> a écrit :

> # type my_int = private int;;
> 
> I get the message : "This fixed type is not an object or variant"
> 
> 1. The message is very obscure
> 2. why this syntax is not implemented as it should be ?
The syntax seems to be implemented as what the documentation says.
See http://caml.inria.fr/pub/docs/manual-ocaml/manual021.html#htoc99: 
"Private types

type-representation	::=	...  
 	∣	 = private constr-decl  { | constr-decl }  
 	∣	 = private { field-decl  { ; field-decl } }
"
i.e. at the moment you can write 'type foo = private A of int'
or 'type bar = private { a of int }'
but not directly 'type my_int = private int'
(IIRC, there are some technical reasons linked to the internal
representation of ocaml syntax tree for that) 
As said above, you have to wait (or try the cvs version) for ocaml 3.11
to be able to declare any type definition as private.
-- 
E tutto per oggi, a la prossima volta.
Virgile

Re: [Caml-list] Private type syntax and error message

[Colonna Francois]

Le vendredi 12 septembre 2008 à 15:43 +0200, Colonna Francois a écrit :
> Hello,
> 
> if, as I found in the documentation, I write :
>  
> # type my_int = private int;;
> 
> I get the message : "This fixed type is not an object or variant"
> 
> 1. The message is very obscure
> 2. why this syntax is not implemented as it should be ?
> 

Sorry,

I found in http://caml.inria.fr/mantis/view.php?id=4584 the answer to my
question. X. Leroy said there :

The "private type abbreviations" feature of 3.11 ....

  type t = private float
 

So, I shall wait a few monthes. No problem.
Thanks any ways to thoses who answered.

Best,
François Colonna

Re: [Caml-list] Private type syntax and error message

[Jon Harrop]

On Friday 12 September 2008 14:43:19 Colonna Francois wrote:
> Hello,
>
> if, as I found in the documentation, I write :
>
> # type my_int = private int;;

Where does that appear in the documentation? Google returns zero hits...

> I get the message : "This fixed type is not an object or variant"
>
> 1. The message is very obscure

How would you write it more clearly?

> 2. why this syntax is not implemented as it should be ?

What do you expect it to do that might work? If it created an abstract type 
the type would be useless, having no way to construct or destructure values 
of that type...

-- 
Dr Jon Harrop, Flying Frog Consultancy Ltd.
http://www.ffconsultancy.com/?e