Foldable and traversable
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{-# LANGUAGE DeriveFoldable #-}
{-# LANGUAGE DeriveFunctor #-}
{-# LANGUAGE DeriveTraversable #-}
module Main
( main
) where
data Tree a = a :<<: [Tree a]
deriving (Show, Functor, Foldable, Traversable)
main :: IO ()
main = do
putStr "Example tree: "
print example
putStr "\nEach element transformed (fmap): "
print (fmap negate example)
putStr "\nAll elements summed (foldl): "
print (foldl (+) 0 example)
putStr "\nAll elements printed, then the result of that printed (traverse): "
print =<< traverse print example
where
example :: Tree Int
example = 1 :<<: [2 :<<: [], 3 :<<: [4 :<<: [], 5 :<<: []], 6 :<<: []]
Haskell
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