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