On Mon, Oct 4, 2010 at 9:04 PM, Dean Herington
With respect to "datatype destructing" functions, the Prelude has:
maybe :: b -> (a -> b) -> Maybe a -> b either :: (a -> c) -> (b -> c) -> Either a b -> c
which suggests the following signatures for the analogues for Bool and list types:
bool :: a -> a -> Bool -> a list :: b -> (a -> [a] -> b) -> [a] -> b
This suggestion is not so clear to me. Maybe and Either are both non-recursive, so the Church and Scott encodings coincide. You've written the Scott encoding of list. The Church encoding should look familiar: list :: b -> (a -> b -> b) -> [a] -> b Intuitively, a Scott encoding peels off one layer of datatype, whereas a Church encoding flattens down a whole recursive structure. Church encodings are more powerful -- you can do more without requiring a fixed point operator. Just to be clear, I am not arguing anything other than "maybe" and "either" don't readily generalize to "list" because of list's recursiveness. Luke