Klaus Ostermann wrote: > I am not a Haskell expert, and I am currently exploring type classes > and need some advice.
The most important advice is probably to point out that a `class' in
Haskell is roughly comparable to an `interface' in Java, but not to a
`class'.
> class Node n where
> isConnectedTo :: Graph g n e => g -> n -> e -> Bool
This is not what you want. The type says: "Every node can find out
whether it is connected to a given edge _in_any_type_of_graph_", which
is clearly impossible given that your Graph class has no methods.
Is your setting the notion of being a `Node' only makes sense in
connection with a type of `Graph'. The right thing to so is probably to
drop the classes `Edge' and `Node' and put their methods into the
`Graph' class.
class Graph g n e | g -> n e where
isConnectedTo :: g -> n -> e -> Bool
n1 :: g -> e -> n
n2 :: g -> e -> n
Udo.
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