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] [EMAIL PROTECTED]
system administrator [openafs,heimdal,too many hats] [EMAIL PROTECTED]
electrical and computer engineering, carnegie mellon university KF8NH
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