Changes to Typeable

José Pedro Magalhães jpm at
Thu Nov 1 09:31:00 CET 2012

On Thu, Nov 1, 2012 at 8:28 AM, Christian Maeder
<Christian.Maeder at>wrote:

> Am 29.10.2012 10:05, schrieb José Pedro Magalhães:
> [...]
>  It's been proposed to remove the possibility to derive Typeable or write
>> instances for it.
>> I'm supposing the way that this would be implemented would be:
>> 7.8: Any uses of "deriving Typeable" would give rise to a warning saying
>> that it is no longer
>> necessary. Any instances of Typeable would give rise to a warning saying
>> that this code
>> is being ignored, and replaced by an internal Typeable instance.
>> Packages might break,
>> or change runtime behaviour due to this change.
>> 7.10: Explicit uses of "deriving Typeable" or instances are an error.
> I would vote against making "deriving Typeable" an error as this would
> break a lot of existing code (and is recommended by current deprecation
> warnings).
> Ignoring it (with or without warning) is the right thing to do (IMHO).
> Furthermore there's a language flag DerivingTypeable, that should be
> ignored, too, then.

The flag is actually DeriveDataTypeable, and Data isn't changing, so that
flag must stay
(or be renamed to DeriveData...)


> Cheers Christian
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