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{-# LANGUAGE DeriveFunctor, DeriveFoldable #-}
module Main where
import Prelude hiding (sum)
import Data.Foldable
-- Derive Foldable for a simple data type
data List a = Nil | Cons a (List a)
deriving (Functor,Foldable,Show)
someList = Cons 1 (Cons 1 (Cons 2 (Cons 3 Nil)))
main = print (sum someList)
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