On Jan 24, 2007, at 19:34 , John Ky wrote:
class Node -- yadda yadda
data Branch = Branch { name :: String, description :: String, children :: [AnyNode] } data Leaf = Leaf { name :: String, value :: String }
The problem here is I can't use the same 'name' field for both Branch and Leaf. Ideally I'd like the name field in the Node class, but it doesn't seem that Haskell classes are for that sort of thing.
I'm probably missing something, but: (a) Why not: data ANode = Branch { name :: String, description :: String, children :: [AnyNode] } | Leaf { name :: String, value :: String } -- this reuse is legal -- leaving Node available if you still need it (b) I think you *can* do this with a class: class Node a where name :: a -> String data Branch = Branch { brName :: String, ... } data Leaf = Leaf { lName :: String, ... } instance Node Branch where name = brName instance Node Leaf where name = lName -- brandon s. allbery [linux,solaris,freebsd,perl] allbery@kf8nh.com system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH