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{-# LANGUAGE DeriveFoldable #-}
{-# LANGUAGE DeriveTraversable #-}
{-# LANGUAGE TypeFamilies #-}
module Data.StrictList where
import qualified Control.Foldl as L
import qualified GHC.Exts
import Control.Foldl (Fold (Fold))
import Data.Aeson (FromJSON, ToJSON, parseJSON, toJSON)
import Data.Foldable (toList)
import Prelude hiding (last, (++))
data StrictList a = Nil | Cons !a !(StrictList a)
deriving (Eq, Show, Functor, Foldable, Traversable)
instance GHC.Exts.IsList (StrictList a) where
type Item (StrictList a) = a
toList = toList
fromList = fromList
instance FromJSON a => FromJSON (StrictList a) where
parseJSON = fmap fromList . parseJSON
instance ToJSON a => ToJSON (StrictList a) where
toJSON = toJSON . toList
instance Monoid (StrictList a) where
mempty = Nil
mappend = (++)
instance Applicative StrictList where
pure x = Cons x Nil
Cons f fs <*> Cons x xs = Cons (f x) (fs <*> xs)
_ <*> _ = Nil
(++) :: StrictList a -> StrictList a -> StrictList a
(++) Nil ys = ys
(++) (Cons x xs) ys = Cons x (xs ++ ys)
snocFold :: Fold a (StrictList a)
snocFold = Fold step Nil id
where
step xs x = xs `mappend` Cons x Nil
consFold :: Fold a (StrictList a)
consFold = Fold (flip Cons) Nil id
fromList :: [a] -> StrictList a
fromList = L.fold snocFold
head :: StrictList a -> Maybe a
head Nil = Nothing
head (Cons x _) = Just x
tail :: StrictList a -> StrictList a
tail Nil = Nil
tail (Cons _ xs) = xs
last :: StrictList a -> Maybe a
last = L.fold L.last
reverse :: StrictList a -> StrictList a
reverse = L.fold consFold
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