019f8fd211
git-subtree-dir: users/wpcarro git-subtree-mainline:464bbcb15cgit-subtree-split:24f5a642afChange-Id: I6105b3762b79126b3488359c95978cadb3efa789
60 lines
1.6 KiB
Haskell
60 lines
1.6 KiB
Haskell
module BasicLibrariesScratch where
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import Data.Function ((&))
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--------------------------------------------------------------------------------
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newtype DList a = DL { unDL :: [a] -> [a] }
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instance (Show a) => Show (DList a) where
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show (DL x) = "DL " ++ show (x [])
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-- | Create an empty difference list.
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emptyDList :: DList a
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emptyDList = DL $ \xs -> xs
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{-# INLINE emptyDList #-}
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-- | Create a difference list with `x` as the only member.
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singleton :: a -> DList a
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singleton x = DL $ \xs -> x : xs
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{-# INLINE singleton #-}
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-- | Convert the DList into a list.
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toList :: DList a -> [a]
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toList (DL unDL) = unDL mempty
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{-# INLINE toList #-}
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-- | Add an element to the end of a DList.
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infixr `snoc`
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snoc :: a -> DList a -> DList a
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snoc x (DL xs) = DL $ \ys -> xs (x : ys)
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{-# INLINE snoc #-}
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-- | Add an element to the beginning of a DList.
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infixr `cons`
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cons :: a -> DList a -> DList a
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cons x (DL xs) = DL $ \ys -> x : xs ys
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{-# INLINE cons #-}
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-- | Combine two DLists together.
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append :: DList a -> DList a -> DList a
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append (DL xs) (DL ys) = DL $ \zs -> zs & ys & xs
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{-# INLINE append #-}
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--------------------------------------------------------------------------------
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data Queue a =
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Queue { one :: [a]
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, two :: [a]
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} deriving (Show, Eq)
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emptyQueue :: Queue a
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emptyQueue = Queue mempty mempty
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enqueue :: a -> Queue a -> Queue a
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enqueue x (Queue en de) = Queue (x:en) de
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dequeue :: Queue a -> Maybe (a, Queue a)
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dequeue (Queue [] []) = Nothing
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dequeue (Queue en []) =
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let (d:de) = reverse en
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in Just (d, Queue de [])
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dequeue (Queue en (d:de)) = Just (d, Queue en de)
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