Tim Newsham wrote:
I know the short-term answer is "use TH" to derive folds if I want them, but I think such an important concept should probably be part of the language.
If you don't mind the hairy code, there's always this generic answer from #haskell almost a year ago: http://hpaste.org/7682 You'd need to hook it up with a preprocessor script since it's a String->String function. It should be pretty easy to rewrite that into TH code in order to clean it up. I agree, it'd be nice to have it as a standard deriving clause, but since every fold has a different type it's challenging to make it fit into the language rather than being a wart. Some of the stuff in Data.Generics, Data.Typable, etc might could help. If you come up with anything you like, it shouldn't be too hard to (convince someone to) convert the logic into a language extension. -- Live well, ~wren