How to access nodes edges of dot format graph (Generalised ) in haskell

Question

I want to access the nodes, edges and properties of 'xDotGraph' (G.DotGraph) and set those again. Here is Haskell code that prints dot format graph using graphviz:

$ cat example.dot
 digraph {
     a [type1="", type2=""];
     b [type1="", type2=""];
     a -> b [label=""];
 }

import Data.GraphViz
import Data.Text.IO as T
import qualified Data.Text.Lazy as B
import qualified Data.Text.Lazy.IO as L
import qualified Data.GraphViz.Types.Generalised as G
import Data.GraphViz.Printing

xDotText <- L.readFile "example.xdot"
let xDotGraph = parseDotGraph xDotText :: G.DotGraph String
T.putStrLn $ renderDot $ toDot xDotGraph

Answer 1

This works for me (mostly identical to your code but there are a few changes):

#!/usr/bin/env stack
{- stack runghc --resolver lts-6.0 --package graphviz
 -}
import Data.GraphViz
import Data.Text.IO as T
import qualified Data.Text.Lazy as B
import qualified Data.Text.Lazy.IO as L
import qualified Data.GraphViz.Types.Generalised as G
import Data.GraphViz.Printing
import Data.GraphViz.Types

main = do
  xDotText <- L.readFile "example.dot"
  let xDotGraph = parseDotGraph xDotText :: G.DotGraph String
  L.putStrLn $ renderDot $ toDot xDotGraph
  print $ graphNodes xDotGraph
  print $ graphEdges xDotGraph