On 29-07-2014 20:41, Stephen Paul Weber wrote:
instance {-# OVERLAPPABLE #-} Show a => Show [a] where ...
instance {-# OVERLAPPING #-} Show [Char] where ...
This, to me, is an admission that developers are not going to want to turn overlapping on globally in general, and so the current language extensions would not make sense to get adopted into the core language at any point. I agree with this idea, and so would second the proposal mentioned at http://www.reddit.com/r/haskell/comments/2c136i/xoverlappinginstances_and_xi... that a language extension that adds actual keywords to tag instances that should be allowed to overlap be added, instead of resorting to pragmas. This seems like an approach that could be useful in general and one could imagine moving "past" an extension to the core language at some point, potentially.
OTOH, the pragma is mostly harmless for older GHC versions, while the keyword approach needs a preprocessor. -- Felipe.