On 11/1/06, Simon Peyton-Jones
The thread about "stand-alone" deriving is long-ish now, so I have summarised the issues here: http://haskell.org/haskellwiki/GHC/StandAloneDeriving
I think it is difficult to discuss things via a Wiki. I tried to add my comments to the page and it took a lot of edits due to a collision with BrianH's edit. Plus, it is not clear to me how agreement is to be indicated. For example, I think that Brian H's idea really good. Basically, the syntax for instances and derived instances would be identical, but derived instances would just omit the "where" clause, while non-derived instances would need the "where" clause. For that to work, the rules for when a context is required need to be the same for derived and non-derived instances, which I also think is a good idea. It is a much better idea than my "derive instance" suggestion, and I no longer support it. - Brian Smith