Language/Haskell/TH/Lib/Map.hs

    {-# LANGUAGE BangPatterns #-}

    -- This is a non-exposed internal module
    --
    -- The code in this module has been ripped from containers-0.5.5.1:Data.Map.Base [1] almost
    -- verbatimely to avoid a dependency of 'template-haskell' on the containers package.
    --
    -- [1] see https://hackage.haskell.org/package/containers-0.5.5.1
    --
    -- The original code is BSD-licensed and copyrighted by Daan Leijen, Andriy Palamarchuk, et al.

    module Language.Haskell.TH.Lib.Map
        ( Map
        , empty
        , insert
        , Language.Haskell.TH.Lib.Map.lookup
        ) where

    data Map k a  = Bin {-# UNPACK #-} !Size !k a !(Map k a) !(Map k a)
                  | Tip

    type Size     = Int

    empty :: Map k a
    empty = Tip
    {-# INLINE empty #-}

    singleton :: k -> a -> Map k a
    singleton k x = Bin 1 k x Tip Tip
    {-# INLINE singleton #-}

    size :: Map k a -> Int
    size Tip              = 0
    size (Bin sz _ _ _ _) = sz
    {-# INLINE size #-}

    lookup :: Ord k => k -> Map k a -> Maybe a
    lookup = go
      where
        go _ Tip = Nothing
        go !k (Bin _ kx x l r) = case compare k kx of
          LT -> go k l
          GT -> go k r
          EQ -> Just x
    {-# INLINABLE lookup #-}

    insert :: Ord k => k -> a -> Map k a -> Map k a
    insert = go
      where
        go :: Ord k => k -> a -> Map k a -> Map k a
        go !kx x Tip = singleton kx x
        go !kx x (Bin sz ky y l r) =
            case compare kx ky of
                LT -> balanceL ky y (go kx x l) r
                GT -> balanceR ky y l (go kx x r)
                EQ -> Bin sz kx x l r
    {-# INLINABLE insert #-}

    balanceL :: k -> a -> Map k a -> Map k a -> Map k a
    balanceL k x l r = case r of
      Tip -> case l of
               Tip -> Bin 1 k x Tip Tip
               (Bin _ _ _ Tip Tip) -> Bin 2 k x l Tip
               (Bin _ lk lx Tip (Bin _ lrk lrx _ _)) -> Bin 3 lrk lrx (Bin 1 lk lx Tip Tip) (Bin 1 k x Tip Tip)
               (Bin _ lk lx ll@(Bin _ _ _ _ _) Tip) -> Bin 3 lk lx ll (Bin 1 k x Tip Tip)
               (Bin ls lk lx ll@(Bin lls _ _ _ _) lr@(Bin lrs lrk lrx lrl lrr))
                 | lrs < ratio*lls -> Bin (1+ls) lk lx ll (Bin (1+lrs) k x lr Tip)
                 | otherwise -> Bin (1+ls) lrk lrx (Bin (1+lls+size lrl) lk lx ll lrl) (Bin (1+size lrr) k x lrr Tip)

      (Bin rs _ _ _ _) -> case l of
               Tip -> Bin (1+rs) k x Tip r

               (Bin ls lk lx ll lr)
                  | ls > delta*rs  -> case (ll, lr) of
                       (Bin lls _ _ _ _, Bin lrs lrk lrx lrl lrr)
                         | lrs < ratio*lls -> Bin (1+ls+rs) lk lx ll (Bin (1+rs+lrs) k x lr r)
                         | otherwise -> Bin (1+ls+rs) lrk lrx (Bin (1+lls+size lrl) lk lx ll lrl) (Bin (1+rs+size lrr) k x lrr r)
                       (_, _) -> error "Failure in Data.Map.balanceL"
                  | otherwise -> Bin (1+ls+rs) k x l r
    {-# NOINLINE balanceL #-}

    balanceR :: k -> a -> Map k a -> Map k a -> Map k a
    balanceR k x l r = case l of
      Tip -> case r of
               Tip -> Bin 1 k x Tip Tip
               (Bin _ _ _ Tip Tip) -> Bin 2 k x Tip r
               (Bin _ rk rx Tip rr@(Bin _ _ _ _ _)) -> Bin 3 rk rx (Bin 1 k x Tip Tip) rr
               (Bin _ rk rx (Bin _ rlk rlx _ _) Tip) -> Bin 3 rlk rlx (Bin 1 k x Tip Tip) (Bin 1 rk rx Tip Tip)
               (Bin rs rk rx rl@(Bin rls rlk rlx rll rlr) rr@(Bin rrs _ _ _ _))
                 | rls < ratio*rrs -> Bin (1+rs) rk rx (Bin (1+rls) k x Tip rl) rr
                 | otherwise -> Bin (1+rs) rlk rlx (Bin (1+size rll) k x Tip rll) (Bin (1+rrs+size rlr) rk rx rlr rr)

      (Bin ls _ _ _ _) -> case r of
               Tip -> Bin (1+ls) k x l Tip

               (Bin rs rk rx rl rr)
                  | rs > delta*ls  -> case (rl, rr) of
                       (Bin rls rlk rlx rll rlr, Bin rrs _ _ _ _)
                         | rls < ratio*rrs -> Bin (1+ls+rs) rk rx (Bin (1+ls+rls) k x l rl) rr
                         | otherwise -> Bin (1+ls+rs) rlk rlx (Bin (1+ls+size rll) k x l rll) (Bin (1+rrs+size rlr) rk rx rlr rr)
                       (_, _) -> error "Failure in Data.Map.balanceR"
                  | otherwise -> Bin (1+ls+rs) k x l r
    {-# NOINLINE balanceR #-}

    delta,ratio :: Int
    delta = 3
    ratio = 2