Problem:
Score : 600 points

Problem Statement

We have a tree with N vertices. The i-th edge connects Vertex A_i and B_i bidirectionally.

Takahashi is standing at Vertex u, and Aoki is standing at Vertex v.

Now, they will play a game of tag as follows:

1. If Takahashi and Aoki are standing at the same vertex, the game ends. Otherwise, Takahashi moves to a vertex of his choice that is adjacent to his current vertex.

2. If Takahashi and Aoki are standing at the same vertex, the game ends. Otherwise, Aoki moves to a vertex of his choice that is adjacent to his current vertex.

3. Go back to step 1.

Takahashi performs his moves so that the game ends as late as possible, while Aoki performs his moves so that the game ends as early as possible.

Find the number of moves Aoki will perform before the end of the game if both Takahashi and Aoki know each other's position and strategy.

It can be proved that the game is bound to end.

Constraints

2 \leq N \leq 10^5

1 \leq u,v \leq N

u \neq v

1 \leq A_i,B_i \leq N

The given graph is a tree.

Input

Input is given from Standard Input in the following format:

N u v
A_1 B_1
:
A_{N-1} B_{N-1}

Output

Print the number of moves Aoki will perform before the end of the game.

Sample Input 1

5 4 1
1 2
2 3
3 4
3 5

Sample Output 1

2

If both players play optimally, the game will progress as follows:

Takahashi moves to Vertex 3.

Aoki moves to Vertex 2.

Takahashi moves to Vertex 5.

Aoki moves to Vertex 3.

Takahashi moves to Vertex 3.

Here, Aoki performs two moves.

Note that, in each move, it is prohibited to stay at the current vertex.

Sample Input 2

5 4 5
1 2
1 3
1 4
1 5

Sample Output 2

1

Sample Input 3

2 1 2
1 2

Sample Output 3

0

Sample Input 4

9 6 1
1 2
2 3
3 4
4 5
5 6
4 7
7 8
8 9

Sample Output 4

5

Solution in Haskell (GHC 7.10.3) (judge verdict: Accepted)

{-# LANGUAGE
  ScopedTypeVariables, BangPatterns, TupleSections, ExplicitForAll,
  LambdaCase, MultiWayIf, Unsafe, RecordWildCards, FlexibleContexts, CPP,
  NoMonomorphismRestriction, GADTs, PatternGuards, MagicHash, UnboxedTuples,
  RankNTypes, EmptyDataDecls, EmptyCase, ViewPatterns, PolyKinds,
  TypeFamilies, OverloadedStrings, FlexibleInstances, UndecidableInstances,
  DefaultSignatures, GeneralizedNewtypeDeriving, StandaloneDeriving,
  DeriveGeneric, DeriveFunctor, DeriveDataTypeable, DeriveFoldable,
  DeriveTraversable, DeriveDataTypeable, FlexibleInstances,
  MultiParamTypeClasses #-}
{-# OPTIONS_GHC -O2 #-}

import Prelude
import Data.Bits
import Data.List
import Data.Maybe
import Data.Tuple
import Data.Ord
import Data.Int
import Data.Word
import Data.Char
import Data.Ratio
import Data.Function
import Data.STRef
import Data.IORef
import Data.Monoid
import Data.Functor
import Data.Data
import Data.Typeable
import GHC.Generics
import System.IO
import Control.Arrow
import Control.Applicative
import Control.Monad
import Control.Monad.Primitive
import Control.Monad.State.Strict
import Control.Monad.ST
import Control.Monad.ST.Lazy (strictToLazyST, lazyToStrictST)
import qualified Control.Monad.ST.Lazy as STL
-- import Control.Monad.ST.Safe
import Control.DeepSeq
import Data.Coerce
import qualified Data.ByteString.Char8 as BS
import qualified Data.ByteString.Lazy.Char8 as BSL
import qualified Data.ByteString.Builder as BSB
import Data.IntMap (IntMap)
import qualified Data.IntMap.Strict as IMS
import qualified Data.IntMap.Lazy as IML
import Data.IntSet (IntSet)
import qualified Data.IntSet as IS
import qualified Data.Sequence as Seq
import Data.Sequence (Seq)
import qualified Data.Array.IArray as A
import qualified Data.Array.MArray.Safe as A
import qualified Data.Array.MArray as A
import Data.Array (Array)
import Data.Array.Unboxed (UArray)
import Data.Array.IArray (IArray)
import Data.Array.MArray.Safe (MArray)
import Data.Array.IO.Safe (IOArray, IOUArray)
import Data.Array.ST.Safe (STArray, STUArray, runSTArray, runSTUArray)
import qualified Data.Vector as V
import qualified Data.Vector.Mutable as VM
import qualified Data.Vector.Unboxed as VU
import qualified Data.Vector.Unboxed.Mutable as VUM
import qualified Data.Vector.Storable as VS
import qualified Data.Vector.Storable.Mutable as VSM
import qualified Data.Vector.Primitive as VP
import qualified Data.Vector.Primitive.Mutable as VPM
import qualified Data.Vector.Generic as VG
import qualified Data.Vector.Generic.Mutable as VGM
import qualified Data.Vector.Fusion.Bundle.Monadic as VFBM
import qualified Data.Vector.Fusion.Bundle as VFB
import qualified Data.Vector.Fusion.Stream.Monadic as VFSM
import qualified Data.Vector.Fusion.Bundle.Size as VFBS
import qualified Data.Vector.Fusion.Util as VFU
import qualified Data.Attoparsec.ByteString.Char8 as Atto
import Debug.Trace
import GHC.Exts (build, Int(..), Int#,
                 (+#), (*#), (-#), (<#), (>=#), (==#), quotRemInt#,
                 remInt#, uncheckedIShiftRL#, andI#, orI#,
                isTrue#)
rIntS1 = subtract 1 <$> rIntS
main :: IO ()
main = do
  (n,u,v) <- fromJust . evalStateT (liftA3 (,,) rIntS rIntS1 rIntS1)
    <$> BS.getLine
  (tree, depths) <- getTreeWithDepths n v
    $ fromJust . evalStateT (liftA3 (,,) rIntS1 rIntS1 $ pure ())
    <$> BS.getLine
  let depU = depths VU.! u
      anc = VU.last
            $ VU.iterateN (1 + (depU - 1) `shiftR` 1)
              (fst . fromJust . parentInTree tree) u
      depthMax !d x = VU.maximum $ VU.cons d $ VU.map (depthMax $ d+1)
        $ VU.map fst $ childrenInTree tree x
      depGoal = depthMax (depths VU.! anc) anc
  print $ depGoal - 1
  return ()

type Vertex = Int
data GraphData d = GraphData {-# UNPACK #-} !(VU.Vector (Vertex,d))
                             {-# UNPACK #-} !(VU.Vector Int)
data MGraphData s d = MGraphData {-# UNPACK #-} !(VUM.MVector s (Vertex,d))
                                 {-# UNPACK #-} !(VU.Vector Int)
data TreeData d = TreeData {-# UNPACK #-} !Vertex
                           {-# UNPACK #-} !(GraphData d)



parentInTree :: (VU.Unbox d)
  => TreeData d -> Vertex -> Maybe (Vertex,d)
parentInTree (TreeData root (GraphData connTable degCount)) vert
  | vert == root = Nothing
  | otherwise    = Just $! connTable VU.! (degCount VU.! vert)

childrenInTree :: (VU.Unbox d)
  => TreeData d -> Vertex -> VU.Vector (Vertex,d)
childrenInTree (TreeData root (GraphData connTable degCount)) vert
  = VU.slice beg (end-beg) connTable
  where
    !end = degCount VU.! (vert+1)
    !beg | vert == root = degCount VU.! vert
         | otherwise    = 1 + degCount VU.! vert

edgesOut :: (VU.Unbox d)
  => GraphData d -> Vertex -> VU.Vector (Vertex,d)
edgesOut (GraphData connTable degCount) vert
  = VU.slice beg (end-beg) connTable
  where
    !end = degCount VU.! (vert+1)
    !beg = degCount VU.! vert

type Depth = Int
{-# INLINE getTreeWithDepths #-}
getTreeWithDepths :: (PrimMonad m, VU.Unbox d)
  => Int -> Vertex -> (m (Int,Int,d)) -> m (TreeData d,VU.Vector Depth)
getTreeWithDepths !numVert !root getEdge = do
  !gd <- getUndirectedGraphMut numVert (numVert-1) getEdge
  !depths <- dfsFindTreeAndDepthInMGraph gd root
  !gdFrozen <- unsafeFreezeGraphData gd
  return (TreeData root gdFrozen, depths)

dfsFindTreeAndDepthInMGraph :: (PrimMonad m, VU.Unbox d)
  => MGraphData (PrimState m) d -> Vertex -> m (VU.Vector Depth)
dfsFindTreeAndDepthInMGraph (MGraphData connTable degCount) !root = do
  depths <- VUM.replicate (VU.length degCount - 1) (-1)
  let dfs !parent !this !depth = do
        !prevDepth <- VUM.read depths this
        when (prevDepth < 0) $ do
          VUM.unsafeWrite depths this depth
          let !beg = VU.unsafeIndex degCount this
              !end = VU.unsafeIndex degCount (this+1) - 1
          forM_ [beg..end] $ \ !i -> do
            (!vertex,!d) <- VUM.read connTable i
            if vertex == parent
              then do !vbeg <- VUM.unsafeRead connTable beg
                      VUM.unsafeWrite connTable beg (vertex,d)
                      VUM.unsafeWrite connTable i vbeg
              else dfs this vertex (depth+1)
  dfs (-1) root 0
  VU.unsafeFreeze depths

{-# INLINE unsafeFreezeGraphData #-}
unsafeFreezeGraphData :: (PrimMonad m, VU.Unbox d) =>
  MGraphData (PrimState m) d -> m (GraphData d)
unsafeFreezeGraphData (MGraphData connTable degCount)
  = (`GraphData` degCount) <$!> VU.unsafeFreeze connTable 

{-# INLINE getDirectedGraphBidir #-}
getDirectedGraphBidir :: (PrimMonad m, VU.Unbox d)
  => Int -> Int -> (m (Int,Int,d))
  -> m (GraphData d, GraphData d)
getDirectedGraphBidir !numVert !numEdges getEdge = do
  (!forward,!backward) <- getDirectedGraphMutBidir numVert numEdges getEdge
  !forwardImmut <- unsafeFreezeGraphData forward
  !backwardImmut <- unsafeFreezeGraphData backward
  return $! (forwardImmut, backwardImmut)

{-# INLINE getDirectedGraphForward #-}
getDirectedGraphForward :: (PrimMonad m, VU.Unbox d) =>
  Int -> Int -> m (Int,Int,d) -> m (GraphData d)
getDirectedGraphForward !numVert !numEdges getEdge = do
  getDirectedGraphMutForward numVert numEdges getEdge >>= unsafeFreezeGraphData


{-# INLINE getUndirectedGraph #-}
getUndirectedGraph
  :: (PrimMonad m, VU.Unbox d) =>
  Int -> Int -> (m (Int,Int,d)) -> m (GraphData d)
getUndirectedGraph !numVert !numEdges getEdge
  = getUndirectedGraphMut numVert numEdges getEdge >>= unsafeFreezeGraphData

{-# INLINE getUndirectedGraphMut #-}
getUndirectedGraphMut
  :: (PrimMonad m, VU.Unbox d)
  => Int -> Int -> (m (Int,Int,d)) -> m (MGraphData (PrimState m) d)
getUndirectedGraphMut !numVert !numEdges getEdge = do
  !degCount <- VUM.replicate (numVert+1) 0
  !connTable <- VUM.new (shiftL numEdges 1)
  write degCount connTable
  MGraphData connTable <$!> VU.unsafeFreeze degCount
  where
    write !degCount !connTable = do
      !temp <- do
        !temp <- VUM.new numEdges
        VU.forM_ (VU.generate numEdges id) $ \ !i -> do
          (!a,!b,!d) <- getEdge
          VUM.unsafeWrite temp i (a,b,d)
          VUM.modify degCount (+1) (a+1)
          VUM.modify degCount (+1) (b+1)
        VU.unsafeFreeze temp
      VU.foldM'
        (\ !total !i -> do
            !di <- VUM.unsafeRead degCount i
            VUM.unsafeWrite degCount i total
            return $! total+di)
        0 (VU.generate (numVert+1) id)
      VU.forM_ temp $ \(!a,!b,!d) -> do
        !ia <- VUM.read degCount (a+1)
        VUM.unsafeWrite degCount (a+1) $! ia+1
        VUM.unsafeWrite connTable ia $! (b,d)
        !ib <- VUM.read degCount (b+1)
        VUM.unsafeWrite degCount (b+1) $! ib+1
        VUM.unsafeWrite connTable ib $! (a,d)
      
getDirectedGraphMutForward :: (PrimMonad m, VU.Unbox d)
  => Int -> Int -> (m (Int,Int,d))
  -> m (MGraphData (PrimState m) d)
getDirectedGraphMutForward !numVert !numEdges getEdge = do
  !degCount <- VUM.replicate (numVert+1) 0
  !connTable <- VUM.new numEdges
  write degCount connTable
  MGraphData connTable <$!> VU.unsafeFreeze degCount
  where
    write !degCount !connTable = do
      !temp <- do
        !temp <- VUM.new numEdges
        VU.forM_ (VU.generate numEdges id) $ \ !i -> do
          (!a,!b,!d) <- getEdge
          VUM.unsafeWrite temp i (a,b,d)
          VUM.modify degCount (+1) (a+1)
        VU.unsafeFreeze temp
      VU.foldM'
        (\ !total !i -> do
            !di <- VUM.unsafeRead degCount i
            VUM.unsafeWrite degCount i total
            return $! total+di)
        0 (VU.generate (numVert+1) id)
      VU.forM_ temp $ \(!a,!b,!d) -> do
        !ia <- VUM.read degCount (a+1)
        VUM.unsafeWrite degCount (a+1) $! ia+1
        VUM.unsafeWrite connTable ia $! (b,d)

getDirectedGraphMutBidir :: (PrimMonad m, VU.Unbox d)
  => Int -> Int -> (m (Int,Int,d))
  -> m (MGraphData (PrimState m) d, MGraphData (PrimState m) d)
getDirectedGraphMutBidir !numVert !numEdges getEdge = do
  !fDegCount <- VUM.replicate (numVert+1) 0
  !fConnTable <- VUM.new numEdges
  !bDegCount <- VUM.replicate (numVert+1) 0
  !bConnTable <- VUM.new numEdges
  write fDegCount fConnTable bDegCount bConnTable
  !forward <- MGraphData fConnTable <$> VU.unsafeFreeze fDegCount
  !backward <- MGraphData bConnTable <$> VU.unsafeFreeze bDegCount
  return $! (forward,backward)
  where
    write !fDegCount !fConnTable !bDegCount !bConnTable = do
      !temp <- do
        !temp <- VUM.new numEdges
        VU.forM_ (VU.generate numEdges id) $ \ !i -> do
          (!a,!b,!d) <- getEdge
          VUM.unsafeWrite temp i (a,b,d)
          VUM.modify fDegCount (+1) (a+1)
          VUM.modify bDegCount (+1) (b+1)
        VU.unsafeFreeze temp
      VU.foldM'
        (\ !total !i -> do
            !di <- VUM.unsafeRead fDegCount i
            VUM.unsafeWrite fDegCount i total
            return $! total+di)
        0 (VU.generate (numVert+1) id)
      VU.foldM'
        (\ !total !i -> do
            !di <- VUM.unsafeRead bDegCount i
            VUM.unsafeWrite bDegCount i total
            return $! total+di)
        0 (VU.generate (numVert+1) id)
      VU.forM_ temp $ \(!a,!b,!d) -> do
        !ia <- VUM.read fDegCount (a+1)
        VUM.unsafeWrite fDegCount (a+1) $! ia+1
        VUM.unsafeWrite fConnTable ia $! (b,d)
        !ib <- VUM.read bDegCount (b+1)
        VUM.unsafeWrite bDegCount (b+1) $! ib+1
        VUM.unsafeWrite bConnTable ib $! (a,d)


#define IL(f) {-# INLINE f #-}; f

IL(putBuilder) = BSB.hPutBuilder stdout

printVecInLines, printVecInSpcSepLn ::
  (VG.Vector v a, ShowAsBuilder a) => v a -> IO ()
IL(printVecInLines) = putBuilder . v2BLines
IL(printVecInSpcSepLn) = putBuilder . v2BSpcSepLn

class ShowAsBuilder a where
  showAsBuilder :: a -> BSB.Builder
  default showAsBuilder :: (Show a) => a -> BSB.Builder
  showAsBuilder = BSB.string8 . show

-- Inconsistent with show
instance (ShowAsBuilder a, VG.Vector v a) => ShowAsBuilder (v a) where
  IL(showAsBuilder) = v2BSpcSep

#define INS(t,f) instance ShowAsBuilder t where { IL(showAsBuilder)=f }
INS(Int,BSB.intDec)
INS(Int8,BSB.int8Dec)
INS(Int16,BSB.int16Dec)
INS(Int32,BSB.int32Dec)
INS(Int64,BSB.int64Dec)
INS(Word,BSB.wordDec)
INS(Word8,BSB.word8Dec)
INS(Word16,BSB.word16Dec)
INS(Word32,BSB.word32Dec)
INS(Word64,BSB.word64Dec)
INS(Integer,BSB.integerDec)
INS(Float,BSB.floatDec)
INS(Double,BSB.doubleDec)
-- INS(String,BSB.string8) -- Inconsistent with Show
-- INS(BS.ByteString,BSB.byteString) -- Inconsistent with Show
-- INS(BSL.ByteString,BSB.lazyByteString) -- Inconsisitent with Show
#undef INS

-- Inconsistent with Show
instance (ShowAsBuilder a, ShowAsBuilder b) => ShowAsBuilder (a,b) where
  IL(showAsBuilder) = showTupAsBuilder
instance (ShowAsBuilder a, ShowAsBuilder b, ShowAsBuilder c) =>
  ShowAsBuilder (a,b,c) where
  IL(showAsBuilder) = showTup3AsBuilder
instance (ShowAsBuilder a, ShowAsBuilder b, ShowAsBuilder c, ShowAsBuilder d) =>
  ShowAsBuilder (a,b,c,d) where
  IL(showAsBuilder) = showTup4AsBuilder

IL(showTupAsBuilderWith)
  :: (a -> BSB.Builder) -> (b -> BSB.Builder) -> (a,b) -> BSB.Builder
showTupAsBuilderWith showA showB
  = \(a,b) -> (showA a <>) $ BSB.char7 ' ' <> showB b
IL(showTupAsBuilder) :: (ShowAsBuilder a, ShowAsBuilder b)
  => (a,b) -> BSB.Builder
showTupAsBuilder = showTupAsBuilderWith showAsBuilder showAsBuilder 

IL(showTup3AsBuilderWith) :: (a -> BSB.Builder) -> (b -> BSB.Builder) ->
  (c -> BSB.Builder) -> (a,b,c) -> BSB.Builder
showTup3AsBuilderWith showA showB showC
  = \(a,b,c) -> (showA a <>) $ (BSB.char7 ' ' <>) $ (showB b <>)
                $ (BSB.char7 ' ' <>) $ showC c
IL(showTup3AsBuilder) :: (ShowAsBuilder a, ShowAsBuilder b, ShowAsBuilder c)
  => (a,b,c) -> BSB.Builder
showTup3AsBuilder
  = showTup3AsBuilderWith showAsBuilder showAsBuilder showAsBuilder

IL(showTup4AsBuilderWith) :: (a -> BSB.Builder) -> (b -> BSB.Builder) ->
  (c -> BSB.Builder) -> (d -> BSB.Builder) -> (a,b,c,d) -> BSB.Builder
showTup4AsBuilderWith showA showB showC showD
  = \(a,b,c,d) -> (showA a <>) $ (BSB.char7 ' ' <>)
                  $ showTup3AsBuilderWith showB showC showD (b,c,d)
IL(showTup4AsBuilder) ::
  (ShowAsBuilder a, ShowAsBuilder b, ShowAsBuilder c, ShowAsBuilder d) =>
  (a,b,c,d) -> BSB.Builder
showTup4AsBuilder = showTup4AsBuilderWith showAsBuilder showAsBuilder
                    showAsBuilder showAsBuilder

v2BSpcSepLn, v2BSpcSep, v2BConcat, v2BLines ::
  (VG.Vector v a, ShowAsBuilder a)
  => v a -> BSB.Builder
IL(v2BSpcSepLn) = v2BSpcSepLnWith showAsBuilder
IL(v2BSpcSep) = v2BSpcSepWith showAsBuilder
IL(v2BConcat) = v2BConcatWith showAsBuilder
IL(v2BLines) = v2BLinesWith showAsBuilder


v2BSpcSepLnWith, v2BSpcSepWith, v2BConcatWith, v2BLinesWith ::
  (VG.Vector v a)
  => (a -> BSB.Builder) -- ^ show function
  -> v a -> BSB.Builder
IL(v2BSpcSepLnWith) = v2BSpcSepPostfWith $ BS.singleton '\n'
IL(v2BSpcSepWith) = v2BSpcSepPostfWith BS.empty
IL(v2BConcatWith) showFct = VG.foldr ((<>) . showFct) mempty
IL(v2BLinesWith) showFct
  = VG.foldr (\ a -> (showFct a <>) . (BSB.char7 '\n' <>)) mempty


v2BSpcSepPostf :: (VG.Vector v a, ShowAsBuilder a)
  => BS.ByteString -- ^ postfix
  -> v a -> BSB.Builder
IL(v2BSpcSepPostf) = (`v2BSpcSepPostfWith` showAsBuilder)

v2BSpcSepPostfWith :: (VG.Vector v a)
  => BS.ByteString -- ^ postfix
  -> (a -> BSB.Builder) -- ^ show function
  -> v a -> BSB.Builder
IL(v2BSpcSepPostfWith) = vecToBuilder BS.empty $ BS.singleton ' '

IL(vecToBuilder) :: (VG.Vector v a)
  => BS.ByteString -- ^ prefix
  -> BS.ByteString -- ^ separator
  -> BS.ByteString -- ^ postfix
  -> (a -> BSB.Builder) -- ^ show function
  -> v a -> BSB.Builder
vecToBuilder !prefix !separator !postfix
  = vecToBuilder_ (BSB.byteString prefix)
                  (BSB.byteString separator)
                  (BSB.byteString postfix)


IL(vecToBuilder_) :: (VG.Vector v a)
  => BSB.Builder -- ^ prefix
  -> BSB.Builder -- ^ separator
  -> BSB.Builder -- ^ postfix
  -> (a -> BSB.Builder) -- ^ show function
  -> v a -> BSB.Builder
vecToBuilder_ !prefix !separator !postfix showFct = \vec -> prefix <>
  VG.foldr
  (\ a rest !prefx -> prefx <> (showFct a <> rest separator))
  (const postfix) vec mempty

IL(evalVals) :: [a] -> [a]
evalVals xs = build $ \c n -> foldr (c $!) n xs
IL(forceVals) :: (NFData a) => [a] -> [a]
forceVals xs = build $ \c n -> foldr (c $!!) n xs

IL(getVecGLn) :: (VG.Vector v a) =>
  Int -> StateT BS.ByteString Maybe a -> IO (v a)
getVecGLn n s = VG.unfoldrN n (runStateT s) <$> BS.getLine
IL(getVecGRest) :: (VG.Vector v a) =>
  Int -> StateT BSL.ByteString Maybe a -> IO (v a)
getVecGRest n s = VG.unfoldrN n (runStateT s) <$> BSL.getContents
IL(getVecLn) :: Int -> StateT BS.ByteString Maybe a -> IO (V.Vector a)
getVecLn = getVecGLn
IL(getVecRest) :: Int -> StateT BSL.ByteString Maybe a -> IO (V.Vector a)
getVecRest = getVecGRest
IL(getVecULn) :: (VU.Unbox a) =>
  Int -> StateT BS.ByteString Maybe a -> IO (VU.Vector a)
getVecULn = getVecGLn
IL(getVecURest) :: (VU.Unbox a) =>
  Int -> StateT BSL.ByteString Maybe a -> IO (VU.Vector a)
getVecURest = getVecGRest

rInt :: StateT BSL.ByteString Maybe Int
IL(rInt) = StateT $ BSL.readInt . BSL.dropWhile (<'!')
rIntS :: StateT BS.ByteString Maybe Int
IL(rIntS) = StateT $ BS.readInt . BS.dropWhile (<'!')

unlessM, whenM :: (Monad m) => m Bool -> m () -> m ()
IL(whenM) = (. flip when) . (>>=)
IL(unlessM) = (. flip unless) . (>>=)

IL(wrA) = A.writeArray
IL(rdA) = A.readArray
IL(mdA) = \arr f !i -> do
  ai <- rdA arr i
  let fai = f ai 
  wrA arr i fai
  return (ai,fai)
{-# INLINE mdA' #-}
mdA' = \arr f !i -> do
  !ai <- rdA arr i
  let !fai = f ai
  wrA arr i fai
  return (ai,fai)
IL(swapA) = \arr !i !j -> do
  ai <- rdA arr i
  wrA arr i =<< rdA arr j
  wrA arr j ai

#define D(f,r,d)\
  IL(f) :: Integral a=>a->d; f=fromIntegral;\
  IL(r) :: String->d; r=read
#define C(f,r,g,h,d) D(f,r,d);\
  g,h :: RealFrac a=>a->d; IL(g)=floor; IL(h)=ceiling
C(_toInteger_,readInteger,floorInteger,ceilInteger,Integer)
C(toInt,readInt,floorInt,ceilInt,Int)
C(toI8,readI8,floorI8,ceilI8,Int8)
C(toI16,readI16,floorI16,ceilI16,Int16)
C(toI32,readI32,floorI32,ceilI32,Int32)
C(toI64,readI64,floorI64,ceilI64,Int64)
C(toWord,readWord,floorWord,ceilWord,Word)
C(toW8,readW8,floorW8,ceilW8,Word8)
C(toW16,readW16,floorW16,ceilW16,Word16)
C(toW32,readW32,floorW32,ceilW32,Word32)
C(toW64,readW64,floorW64,ceilW64,Word64)
D(toDouble,readDouble,Double)
D(toFloat,readFloat,Float)
#undef D
#undef C

#define N(f,g,h,a,m)\
  IL(f) :: forall e i s. (C(a,m)A.Ix i) => (i,i) -> e -> m (a i e);\
  f=A.newArray;\
  IL(g) :: forall e i s. (C(a,m)A.Ix i) => (i,i) -> m (a i e);\
  g=A.newArray_;\
  IL(h) :: forall e i s. (C(a,m)A.Ix i) => (i,i) -> [e] -> m (a i e);\
  h=A.newListArray
#define C(a,m)
N(newIOA,newIOA_,newIOAL,IOArray,IO)
N(newSTA,newSTA_,newSTAL,STArray s,ST s)
#undef C
#define C(a,m) MArray (a) e (m), 
N(newIOUA,newIOUA_,newIOUAL,IOUArray,IO)
N(newSTUA,newSTUA_,newSTUAL,STUArray s,ST s)
#undef C
#undef N

#undef IL