Changes to Typeable

Christian Maeder Christian.Maeder at
Thu Nov 1 09:28:35 CET 2012

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 

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.

Cheers Christian

More information about the Libraries mailing list