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bradparker/NewtypeLists.hs

Created April 2, 2019 05:12
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Newtype Lists
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NewtypeLists.hs
{-# LANGUAGE TupleSections #-}
newtype NonEmpty a = NonEmpty { getNonEmpty :: (a, List a) }
newtype List a = List { getList :: Maybe (NonEmpty a) }
nil :: List a
nil = List Nothing
cons :: a -> List a -> List a
cons a =
List . fmap (NonEmpty . (a,) . uncurry cons . getNonEmpty) . getList
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