Hi, Am Samstag, den 17.08.2013, 20:34 +0200 schrieb Bas van Dijk:

I used the following in the past:

module M (PublicClass(..)) where

class HiddenClass a

class HiddenClass a => PublicClass a where ...

...

Now users of M can't declare instances of PublicClass because they don't have its superclass HiddenClass in scope.

nice idea! Unfortunately not quite what I need; I still want the user to be able to use standalone deriving instances for the class. Greetings, Joachim -- Joachim “nomeata” Breitner mail@joachim-breitner.de • http://www.joachim-breitner.de/ Jabber: nomeata@joachim-breitner.de • GPG-Key: 0x4743206C Debian Developer: nomeata@debian.org

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 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" 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@joachim-breitner.de • http://www.joachim-breitner.de/ Jabber: nomeata@joachim-breitner.de • GPG-Key: 0x4743206C Debian Developer: nomeata@debian.org

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