Hi Stephen,
From: Stephen Tetley
Hi John
I'm not sure about making Binding polymorphic to get Functor, Traversable, Foldable...
While I think you're correct that partitionEithers might not be a useful example to draw from in this case, I'd assume that Binding would be part of a larger syntax-tree, thus there might not be a appropriate single leaf to make the tree polymorphic on. Felipe Lessa's point - to use Uniplate or one of the Generics packages - might be a better candidate for implementing traversals.
I did not consider that, and hadn't seen any other replies when I first replied. If true, I would agree that one of the Generics packages would be the best option. Regardless, I think this is a valid approach. By thinking of data in terms of Functor, Traversable, etc., one can recognize these patterns. Even if Binding is part of a larger syntax tree and can't reasonably be made polymorphic, creating an fmap-like function to do what the OP requested is IMHO simple and idiomatic Haskell. Using Generics then simplifies the implementation. Cheers, John