Benja Fallenstein wrote: > However, if you'd be able to live with > > data CGraph a b = CGraph [LNode a] (Node -> Node -> b) > > then you should be able to write the instance like this-- > > instance Graph CGraph where > empty = CGraph [] (const $ error "Node not in graph") > isEmpty (CGraph xs _) = null xs > labNodes (CGraph xs _) = xs > mkGraph nodes edges = CGraph nodes f where > f x y = fromMaybe (error "Edge not found") (lookup (x,y) edges') > edges' = map (\(x,y,l) -> ((x,y),l)) edges > match x (CGraph nodes f) = case lookup x nodes of > Nothing -> (Nothing, CGraph nodes f) > Just l -> > let nodes' = filter ((/= x) . fst) nodes > left = map (\(y,_) -> (f y x, y)) nodes' > right = map (\(y,_) -> (f x y, y)) nodes' > in (Just (left, x, l, right), CGraph nodes' f)
Thanks for pointing out this proposal. The actual problem is mkGraph that needs all the many edges created beforehand (that's what I wanted to avoid). Cheers Christian _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
