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@blabber
Last active December 14, 2018 05:35
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data List a = Nil
| Cons a (List a)
deriving (Show, Eq)
toList :: List a -> [a]
toList = foldr (\ x y -> x : y ) []
fromList :: [a] -> List a
fromList = foldr (\ x y -> Cons x y ) Nil
reverse' :: List a -> List a
reverse' = foldl (\ x y -> Cons y x) Nil
instance Monoid (List a) where
mempty = Nil
mappend xs ys = foldr (\ x acc -> Cons x acc) ys xs
instance Eq a => EqProp (List a) where
(=-=) = eq
instance Functor List where
fmap _ Nil = Nil
fmap f (Cons x xs) = Cons (f x) (fmap f xs)
instance Applicative List where
pure x = Cons x Nil
Nil <*> _ = Nil
_ <*> Nil = Nil
Cons f fs <*> xs = mappend (fmap f xs) (fs <*> xs)
instance Monad List where
Nil >>= _ = Nil
Cons x xs >>= f = mappend (f x) (xs >>= f)
instance Foldable List where
foldr _ acc Nil = acc
foldr f acc (Cons x xs) = f x (foldr f acc xs)
instance Traversable List where
sequenceA = foldr (\ x acc -> Cons <$> x <*> acc) (pure Nil)
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