1 files changed, 30 insertions, 0 deletions
diff --git a/61-69/67.hs b/61-69/67.hs
new file mode 100644
index 0000000..70186f1
--- /dev/null
+++ b/61-69/67.hs
@@ -0,0 +1,30 @@
+data Tree a = Empty | Branch a (Tree a) (Tree a) deriving (Show, Eq)
+
+treeToString :: Tree Char -> [Char]
+
+treeToString Empty = ""
+treeToString (Branch x Empty Empty) = [x]
+treeToString (Branch x l r) = x:'(':(treeToString l) ++ "," ++ (treeToString r) ++ ")"
+
+stringToTree :: Monad m => [Char] -> m (Tree Char)
+
+stringToTree "" = return (Empty)
+stringToTree [x] = return (Branch x Empty Empty)
+stringToTree x = fmap fst $ parse x
+    where  parse (x:xs)
+             | x == ',' || x == ')' = return (Empty, x:xs)
+           parse (x:y:xs)
+             | y == ',' || y == ')' = return (Branch x Empty Empty, y:xs)
+             | y == '(' = do (lt, ',':xs') <- parse xs
+                             (rt, ')':xs'') <- parse xs'
+                             return (Branch x lt rt, xs'')
+           parse _ = fail "parse error"
+
+
+cbtFromList :: [a] -> Tree a
+
+cbtFromList xs = let (t, xss) = cbt (xs:xss) in t
+                     where cbt ((x:xs):xss) = (Branch x lt rt, xs:xss'')
+                               where (lt, xss') = cbt xss
+                                     (rt, xss'') = cbt xss'
+                           cbt _ = (Empty, [])