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import Data.Map as Map
import Data.Maybe
import Control.Applicative
data Element = A | B | C | D
deriving (Eq, Ord, Show)
addElement :: Element -> Map Element Int -> Map Element Int
addElement = alter ((<|> Just 1) . fmap (+1))
getScore :: Element -> Map Element Int -> Float
getScore e m = fromMaybe 1.0 $ ((1.0/) . fromIntegral) <$> Map.lookup e m
data BinaryTree a = Empty | Node a (BinaryTree a) (BinaryTree a) deriving Show
type ElementTree = BinaryTree Element
type ScoredElementTree = BinaryTree (Element, Float)
assignScores :: ElementTree -> Map Element Int -> (Map Element Int, ScoredElementTree)
assignScores Empty m = (Map.empty, Empty)
assignScores (Node e t1 t2) m = (m', Node (e, getScore e m) t1' t2')
where
(m1, t1') = assignScores t1 m
(m2, t2') = assignScores t2 m
m' = addElement e $ unionWith (+) m1 m2
doAssignScores :: ElementTree -> ScoredElementTree
doAssignScores t = t'
where (m, t') = assignScores t m