[Haskell-cafe] Fwd: The Typeable class is changing

[Thomas DuBuisson]

Alberto G. Corona <agocorona at gmail.com> wrote:
> What to do when the data has been defined in other package and provides no
> Typeable instance?

You'd have to use standalone deriving, which I hope gets into Haskell 201X.

----
module A where

data A = A
----
{-# LANGUAGE StandaloneDeriving, DeriveDataTypeable #-}
module B where

import A
import Data.Typeable

deriving instance Typeable A
----

Cheers,
Thomas



>
> 2011/7/11 Yitzchak Gale <gale at sefer.org>
>>
>> Simon Marlow has announced[1] on the Haskell Libraries
>> list that the Typeable class is changing.
>>
>> The standard way to create a Typeable instance is
>> just to derive it. If you do that, you will not be affected
>> by this change.
>>
>> But it seems that many packages create Typeable
>> instances by explicitly using mkTyCon. If your package
>> does this, it will eventually break, after a deprecation
>> period.
>>
>> Please respond to this thread if you own a package
>> that will be affected by this change.
>>
>> Can someone who has quick access to the entire contents
>> of Hackage please do a grep and find out exactly which
>> packages on Hackage will be affected? Thanks.
>>
>> -Yitz
>>
>> [1] http://www.haskell.org/pipermail/libraries/2011-July/016546.html
>>
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