Re: [Haskell-cafe] Families of type classes

Daniel Fischer schrieb:

I'd prefer (very strongly) something like

class Graph g n e | g -> n, g -> e where isConnectedTo :: g -> n -> e -> Bool -- or perhaps rather without "g" startNode, endNode :: e -> n . . . -- other Methods of interest like nodes, edges, components . . .

with, e.g.

instance Graph (Map node [node]) node (node,node) where . . .

Thanks for the suggestion. This looks good, but it seems as if the "g" needs to occur in every signature, otherwise the interpreter throws a "No instance for ... arising from ..." error if you want to apply the function. Hence startNode would need to be startNode :: g -> e -> n rather than startNode :: e -> n Is there any way to get rid of this dummy argument? Klaus