On 31.07 16:27, Brian Hulley wrote:
None of the above type classes would be compatible with Data.ByteString! (You mentioned this issue before wrt Data.Edison.Seq but it just clicked with me now for the above refactoring.) For compatibility, the element type would need to appear also thus:
class Foldable f_a a | f_a -> a where fold :: (a -> b -> b) -> b -> f_a -> b
With the new System FC (when it is merged) we could make these classes nicer. class ElementType c a | c -> a instance ElementType [a] a instance ElementType ByteString Char instance IArray a e => ElementType (a i e) e class Foldable c where fold :: ElementType c a => (a -> b -> b) -> b -> c -> b This won't work at the moment due to limitations in GHC, but seems like a cleaner solution. - Einar Karttunen