Work on converting inventory list to tree

src/Dodge/Data/DoubleTree.hs

@@ -13,5 +13,8 @@ import Data.Aeson.TH
 data DoubleTree a = DT {_dtValue :: a,_dtLeft :: [DoubleTree a],_dtRight :: [DoubleTree a]}
     deriving (Eq,Ord,Show,Read)
 
+instance Functor DoubleTree where
+    fmap f (DT x l r) = DT (f x) (fmap (fmap f) l) (fmap (fmap f) r)
+
 makeLenses ''DoubleTree
 deriveJSON defaultOptions ''DoubleTree