On Mon, Jul 19, 2010 at 11:29:37AM +0200, Christian Maeder wrote: > I'm for this proposal, although I've got an example where I need this > context, namely for DrIFT to derive a proper context for instances. > > DrIFT doesn't know that the Read instance for Data.Set.Set relies on Ord > of the elements. For > > data Ord symbol => ExtSign sign symbol = ExtSign > { plainSign :: sign > , nonImportedSymbols :: Set.Set symbol > } deriving Show > > DrIFT cannot derive the Read (or our deserialization) instance without > the "Ord symbol =>" context. > > However, ghc is able by "deriving (Show, Read)" to see > > instance (Ord symbol, Read sign, Read symbol) => > Read (ExtSign sign symbol) > > without the context.
Hmm... if you can provide a fix for this I'll integrate it, perhaps a manual annotation will be the only way, I don't think there is any easy way for DrIFT to derive that information otherwise. John -- John Meacham - ⑆repetae.net⑆john⑈ - http://notanumber.net/ _______________________________________________ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime