[hs] tree pretty printing

haskell/ShowTree.hs

@@ -0,0 +1,16 @@
+-- | An ASCII art show function for binary trees.
+
+module ShowTree where
+
+import Data.List
+
+data Tree a = Leaf | Node (Tree a) a (Tree a)
+
+data WidthTree a = Leaf | Node (Tree a) a (Tree a)
+
+showTree :: Int -> Tree a -> String
+showTree pre (Leaf) = (replicate pre ' ') ++ "x"
+showTree pre (Node l x r) = intercalate "\n" (map (replicate pre ' ' ++) ["x", " / \\ ", (showTree pre l ++ "   " ++ showTree pre r)])
+
+instance Show a => Show (Tree a) where
+  show = showTree 0