Hát... ennyivel:

Before:

breakEdgeApart :: Graph -> Edge -> Edge -> Position -> Graph
breakEdgeApart (Graph ns es) e e1 p =
    Graph (replace [oldStart, oldEnd]
          [newStart, newEnd, newNode] ns)
          (replace [e]
          [newEdge1, newEdge2, newIntersectingEdge] es)
    where
        oldStart = start e
        oldEnd   = end e
        newStart = Node (pos oldStart)
                        (replace [e] [newEdge1] (neighbours
                                 oldStart)) Full
        newEnd   = Node (pos oldEnd)
                        (replace [e] [newEdge2] (neighbours
                                 oldEnd)) Full
        newEdge1 = Edge newStart newNode (isHighway e)
        newEdge2 = Edge newNode newEnd (isHighway e)
        newNode  = Node p [newEdge1, newEdge2,
                           newIntersectingEdge] Full
        -- This is the edge that broke the observed edge.
        newIntersectingEdge =
            Edge (start e1) newNode (isHighway e1)After:

breakEdgeWith :: Edge -> Edge -> Node -> State Graph ()
breakEdgeWith edgeToBreak edgeWith newNode = do
  g <- get 
  let
    n1 = start edgeToBreak
    n2 = end edgeToBreak
  disconnect (n1, n2)
  connect (n1, newNode)
  connect (n2, newNode)Még mondjuk nem ellenőriztem le, de az alfüggvények tuti jól működnek, mert megnéztem. Ugye, hogy mennyivel rövidebb? :D