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module Data.DList
( DList(..)
, empty
, singleton
, toList
, cons
, snoc
, append
) where
newtype DList a = DL { unDL :: [a] -> [a] }
empty :: DList a
empty = DL ([] ++)
{-# INLINE empty #-}
singleton :: a -> DList a
singleton x = DL ([x] ++)
{-# INLINE singleton #-}
toList :: DList a -> [a]
toList xsf = unDL xsf []
{-# INLINE toList #-}
-- Prepend a single element to a dlist.
infixr `cons`
cons :: a -> DList a -> DList a
cons x xs = DL ((x:) . unDL xs)
{-# INLINE cons #-}
-- Append a single element to a dlist.
infixl `snoc`
snoc :: DList a -> a -> DList a
snoc xs x = append xs $ singleton x
{-# INLINE snoc #-}
-- Append dlists.
append :: DList a -> DList a -> DList a
append xsf ysf = DL $ (unDL xsf) . (unDL ysf)
{-# INLINE append #-}
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