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{-# LANGUAGE BangPatterns #-}
module Main where
data Tree = Leaf !Int | Fork !Tree !Tree deriving Show
fullTree 0 = Leaf 1
fullTree n = let t = fullTree (n - 1) in Fork t t
flatListNaive (Leaf n) = [n]
flatListNaive (Fork a b) = flatListNaive a ++ flatListNaive b
flatListCons t = flat t []
where
flat (Leaf n) ns = n : ns
flat (Fork a b) ns = flat a (flat b ns)
flatListCons2 t = flat t []
where
flat (Leaf n) = \ns -> n : ns
flat (Fork a b) = \ns -> flat a (flat b ns)
flatListCons3 t = flat t []
where
flat (Leaf n) = (n :)
flat (Fork a b) = flat a . flat b
flatDList (Leaf n) = (n :)
flatDList (Fork a b) = flatDList a . flatDList b
sumList l = loop 0 l
where loop !c [] = c
loop !c (h:t) = loop (c + h) t
sumDList l = loop 0 (l [])
where loop !c [] = c
loop !c (h : t) = loop (c + h) t
main = print $ sumList $ flatListCons3 $ fullTree 26
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