On Thu, 14 Feb 2008, Christian Maeder wrote:
Henning Thielemann wrote:
'gr a b', but 'a' is not an index type. The nodes are indexed by Node which is a synonym for Int. For the tasks I had so far there was no need for the label type 'a', I just needed a more specific index type than Node (=Int), say an enumeration. The library designer seems to appreciate that applications may not need the labels, and provided functions like mkUGraph and type synonyms like Data.Graph.Inductive.Tree.UGr = Gr () (), which seems for me the wrong way around. It would be simple to add labels to an arbitrary indexed but unlabeled graph, say Ix i => gr i.
I agree that Ix (or only Ord) may be desirable as node types, but still some applications may need more sophisticated labels or may want to change the labels associated to nodes.
No problem. If the node labels are in a separate array you can even do in-place updates in ST monad.
For these cases I don't see how you get rid of specializations to "()" without duplicating the library.
The library could provide a record like LabeledGraph i nodeLabel edgeLabel = LG (Gr i) (Array i nodeLabel) (Map (i,i) edgeLabel) with the interface that is now used for (Graph gr). However, I suspect that finding the label for an edge is then less efficient then now.