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+module TreeSearch where
+
+import Data.Tree.Zipper
+import Data.Maybe
+
+-- findTree :: PosType t => (a -> Bool) -> TreePos t a -> Maybe (TreePos t a)
+findTree :: (a -> Bool) -> TreePos Full a -> Maybe (TreePos Full a)
+findTree p loc = if p (label loc)
+ then Just loc
+ else depthFirst loc >>= findTree p
+
+depthFirst :: TreePos Full a -> Maybe (TreePos Full a)
+depthFirst loc = case firstChild loc of
+ Just x -> Just x
+ Nothing -> case next loc of
+ Just x -> Just x
+ Nothing -> case parent loc of
+ Just x -> next x
+ Nothing -> Nothing