How do you represent a graph in Haskell?

Question

It\'s easy enough to represent a tree or list in haskell using algebraic data types. But how would you go about typographically representing a graph? It seems that you need

Answer 1

I like this implementation of a graph taken from here

import Data.Maybe
import Data.Array

class Enum b => Graph a b | a -> b where
    vertices ::  a -> [b]
    edge :: a -> b -> b -> Maybe Double
    fromInt :: a -> Int -> b