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src/Dodge/DoubleTree.hs

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+module Dodge.DoubleTree where
+
+import Dodge.Data.DoubleTree
+
+-- conceptually, in a tree growing from left to right, 
+-- bottom -> top is equated with left -> right.
+-- this does not match with thinking of a list as top -> bottom, so take care
+doubleTreeToIndentList :: DoubleTree a -> [(a,Int,DoubleTreeNodeType)]
+doubleTreeToIndentList = dtIL DTRootNode
+
+dtIL :: DoubleTreeNodeType -> DoubleTree a -> [(a,Int,DoubleTreeNodeType)]
+dtIL nt (DT x l r) = map doindent (concat (headMap (dtIL DTBottomNode) (dtIL DTMidBelowNode) l))
+    ++ [(x,0,nt)] 
+    ++ map doindent (concat (lastMap (dtIL DTTopNode) (dtIL DTMidAboveNode) r))
+  where
+    doindent (a,b,c) = (a,b+1,c)
+
+headMap :: (a -> b) -> (a -> b) -> [a] -> [b]
+headMap f g (x:xs) = f x : map g xs
+headMap _ _ [] = []
+
+lastMap :: (a -> b) -> (a -> b) -> [a] -> [b]
+lastMap _ _ [] = []
+lastMap f _ (x:[]) = [f x]
+lastMap f g (x:xs) = g x : lastMap f g xs
+