Hi Claus, On Wed, Sep 24, 2008 at 07:21:19PM +0100, Claus Reinke wrote:
I've put an example showing how multiple instances can cause Data.Set to go wrong here: http://hackage.haskell.org/trac/ghc/ticket/2356#comment:8
Do you think that that behaviour is OK?
I'm not sure from your reply what your answer to this is. Is it "I don't know whether I think that that behaviour is OK or not"?
Note that I submitted that ticket;-) I think that the behaviour, the Haskell'98 vs Ghc discrepancy, the comments, and this thread, show that the rules need to be specified carefully and clearly,
While that would be helpful, I think that the behaviour you are interested in only works because it would be expensive to fix it (at least, that's how I understand Simon's "So I'm not sure what to do; and the only thing that comes to mind isn't cheap." comment), not because of any unclarity. I'd be interested to see a design that allows for local instances, in a way that doesn't cause problems like in the URL above, but as far as I know none exist yet. Thanks Ian