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.

Cheers Christian