Private classes

[Edward A Kmett]

My usual variant of this is to use

class Foo' a

class Foo' a => Foo a
instance Foo' a => Foo a

and not export Foo'

Sent from my iPhone

On Aug 17, 2013, at 2:34 PM, Bas van Dijk <v.dijk.bas at gmail.com> wrote:

> Hi Joachim,
> 
> I used the following in the past:
> 
> module M (PublicClass(..)) where
> 
> class HiddenClass a
> 
> class HiddenClass a => PublicClass a where
>   ...
> 
> instance HiddenClass SomeType
> 
> instance PublicClass SomeType where 
>   ...
> 
> Now users of M can't declare instances of PublicClass because they don't have its superclass HiddenClass in scope.
> 
> Regards,
> 
> Bas
> 
> On Aug 17, 2013 8:10 PM, "Joachim Breitner" <mail at joachim-breitner.de> wrote:
>> Hi,
>> 
>> for some reason I was under the impression that if I don’t export the
>> methods of a class, then no user of my module can create instances. But
>> I was wrong and in fact they can; the methods will just all be bound to
>> "error ...".
>> 
>> Is there really no way to create a class so that no-one else can create
>> any instances?
>> 
>> Greetings,
>> Joachim
>> 
>> --
>> Joachim “nomeata” Breitner
>>   mail at joachim-breitner.de • http://www.joachim-breitner.de/
>>   Jabber: nomeata at joachim-breitner.de  • GPG-Key: 0x4743206C
>>   Debian Developer: nomeata at debian.org
>> 
>> 
>> _______________________________________________
>> Glasgow-haskell-users mailing list
>> Glasgow-haskell-users at haskell.org
>> http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
> _______________________________________________
> Glasgow-haskell-users mailing list
> Glasgow-haskell-users at haskell.org
> http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.haskell.org/pipermail/glasgow-haskell-users/attachments/20130817/10a1e054/attachment.htm>