On Thu, 2008-09-18 at 15:43 -0300, Andre Nathan wrote:
My Graph type is the following.
data Graph a b = Graph { adjacencies :: Map Int (a, (Map Int b)) , numVertices :: Int , numEdges :: Int }
addVertex :: Int -> a -> State (Graph a b) () addVertex vertex label = do g <- get let adj = Map.insert vertex (label, Map.empty) (adjacencies g) put $ g { adjacencies = adj, numVertices = numVertices g + 1 }
So I'm confused right now about how I should proceed. Any hints regarding that?
To be honest I would not bother with the state monad and just make them pure operations returning new graphs: addVertex :: Int -> a -> Graph a b -> Graph a b It's very common to have this style, ie returning a new/updated structure explicitly rather than implicitly in a state monad. Just look at the Data.Map api for example. If you later want to stick it in a state monad then that would be straightforward but also easy to use directly. Duncan