Hi Dominique, On Mon, Feb 10, 2014 at 04:55:52PM +0100, Dominique Devriese wrote:
Hm. Interesting point, I guess this is the same problem as the whole orphan instances debate... I didn't think of the connection to that problem. Still, I'm convinced there are situations where local instances are *exactly* what we need, so there must be some way to avoid this problem...
If a type class has a clear semantical meaning, what should then be the point of having multiple instances for the same data type? A clear semantical meaning contradicts multiple instances, they would only make reasoning about your code harder. The few use cases where it might be nice to be able to define a new instance aren't IMHO worth the drawbacks. You would just open Haskell for Ruby like monkey patching. Greetings, Daniel