Hi, I'm new to this, but I'll give it a shot.

import Data.Graph.Inductive

There are several ways to build a graph. Let's say, node labels are 'String's and edge labels are 'Double's. Edge labels would be the weights.

grs :: [Gr String Double]

The below four lines generate the same graph. From labeled nodes and edges:

grs = [mkGraph [(2, "start"), (1, "end")] [(2, 1, 1.0)],

insEdge (2, 1, 1.0) $ insNodes [(2, "start"), (1, "end")] empty,

From contexts:

([], 2, "start", [(1.0, 1)]) & (([], 1, "end", []) & empty),

buildGr [([], 2, "start", [(1.0, 1)]), ([], 1, "end", [])]]

Test graph equality:

gr = head grs same = all (equal gr) (tail grs)

You can populate the graph using (&) and ins... functions while using 'newNodes' to get a bunch of unused node indexes ('Node's) to avoid collisions. Deleting nodes also delete all connected edges, but trying to insert an edge to a non-existent node will create an exception. So nodes get in first.

grd = delNode 1 gr -- no problem grd' = insEdge (2, 1, 1.0) grd -- exception

There are some functions to work on edges. For instance, this divides all weights on your graph by 2:

gr2 = emap (/ 2) gr

This makes the graph undirected:

gr2u = undir gr2

There are other map and fold functions. 'gfold' is very powerful. It all depends on your motive though. I don't think there is a straightforward way to tweak individual nodes and edges other than using graph construction tools. Maybe someone could shed a light on this. Thanks, -- Gokhan