使用graphviz可视化Haskell数据树

import Data.GraphViz
import Data.GraphViz.Printing
import Data.GraphViz.Attributes.Complete
import Data.Text.Lazy.IO as L

data Tree a = Leaf a | Node a [Tree a]

exampleTree :: Tree Int
exampleTree = Node 1 [Leaf 2, Node 3 [Leaf 4, Leaf 5]]

treeToGraph :: Tree a -> DotGraph Node
treeToGraph tree = graphElemsToDot params nodes edges
  where
    params = nonClusteredParams { globalAttributes = ga }
    ga = [GraphAttrs [RankDir FromTop]]
    nodes = treeToNodes tree
    edges = treeToEdges tree

treeToNodes :: Tree a -> [LNode a]
treeToNodes (Leaf x) = [(0, x)]
treeToNodes (Node x ts) = (0, x) : concatMap treeToNodesWithParent ts
  where
    treeToNodesWithParent t = let ns = treeToNodes t in map (\(n, l) -> (n + 1, l)) ns

treeToEdges :: Tree a -> [LEdge ()]
treeToEdges (Leaf _) = []
treeToEdges (Node _ ts) = concatMap treeToEdgesWithParent ts
  where
    treeToEdgesWithParent t = let ns = treeToNodes t in map (\(n, _) -> (0, n + 1, ())) ns

exportTree :: FilePath -> Tree a -> IO ()
exportTree filePath tree = runGraphviz (treeToGraph tree) Png filePath

main :: IO ()
main = exportTree "tree.png" exampleTree