[Haskell-cafe] Re: newbie : multi-parameter type classes

Thomas Girod wrote:

Hi there.

I'm trying to define a generic graph type here and don't understand on one error I get. Here I come.

module Graph where

class (Eq n, Eq e) => Topo a n e where empty :: a nodes :: a -> [n] edges :: a -> [e]

This does not work without functional dependencies. Try: class (Eq n, Eq e) => Topo a n e | a -> n e where HTH Christian P.S. Integer comes in via defaulting (of 0 or 1)