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diff --git a/src/Data/Word64RangeMap/Unboxed.hs b/src/Data/Word64RangeMap/Unboxed.hs
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+{-# LANGUAGE FlexibleContexts, FlexibleInstances #-}
+{-# LANGUAGE ConstraintKinds #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE TupleSections #-}
+-- |
+-- A Word64RangeMap is actually a sorted array of arrays
+-- but lookup is done via binary search testing the range.
+-- One way of implementing a sparse array i suppose.
+module Data.Word64RangeMap.Unboxed where
+
+import Data.Word
+import Data.Array.Unboxed
+import qualified Data.Array.MArray as MA
+import Data.Array.MArray (MArray(..))
+import qualified Data.Array.Base as Base
+import Data.Reference
+import Debug.Trace
+import Control.Concurrent.STM
+import Control.Concurrent.STM.TArray
+import Data.Array.IO
+import Data.IORef
+
+type OuterIndex = Int
+type Index = Word64
+type InnerArray b = UArray Index b
+
+-- | Although this type includes a parameter for index, the code assumes bounds start at 0
+-- and the index has 'Integral', and 'Num' instances.
+newtype RefArray r ma i e = RefArray (r (ma i e))
+
+-- convenient contraint kind
+type RangeArray rangeArray m b ref = (IArray UArray b, MArray rangeArray (InnerArray b) m, Reference ref m)
+-- The RangeMap type, to be used with the above constraint
+type RangeMap rangeArray b ref = RefArray ref rangeArray OuterIndex (InnerArray b)
+
+insertArrayAt :: (MA.MArray ma e m, Reference r m, Ix i, Num i, Integral i) =>  RefArray r ma i e -> i -> e -> m ()
+insertArrayAt (RefArray ref) pos e = do
+    ma <- readRef ref
+    (0,n) <- MA.getBounds ma -- irrefutable pattern, assume array starts at 0
+    (esBefore,esAt) <- splitAt (fromIntegral pos) <$> (getElems ma)
+    newMA <- MA.newListArray (0,n+1) (esBefore ++ [e] ++ esAt)
+    writeRef ref newMA
+
+deleteArrayAt :: (MA.MArray ma e m, Reference r m, Ix i, Num i, Integral i) =>  RefArray r ma i e -> i -> m ()
+deleteArrayAt (RefArray ref) pos = do
+    ma <- readRef ref
+    (0,n) <- MA.getBounds ma -- irrefutable pattern, assume array starts at 0
+    (esBefore,esAt) <- splitAt (fromIntegral pos) <$> getElems ma
+    newMA <- MA.newListArray (0,n-1) (esBefore ++ drop 1 esAt)
+    writeRef ref newMA
+
+
+-- forall (ma :: * -> * -> *) i e (r :: * -> *) (m :: * -> *).
+readRefArray :: Reference r m => RefArray r ma i e -> m (ma i e)
+readRefArray (RefArray x) = readRef x
+
+-- forall (ma :: * -> * -> *) i e (r :: * -> *) (m :: * -> *).
+writeRefArray :: Reference r m => RefArray r ma i e -> ma i e -> m ()
+writeRefArray (RefArray x) y = writeRef x y
+
+{-
+instance (Reference r m, MArray ma e m) => MArray (RefArray r ma) e m where
+    getBounds (RefArray r) = readRef r >>= Base.getBounds
+    getNumElements (RefArray r) = readRef r >>= Base.getNumElements
+    unsafeRead (RefArray r) i = readRef r >>= \x -> Base.unsafeRead x i
+    unsafeWrite (RefArray r) i e = modifyRef r (\x -> Base.unsafeWrite x i e >> return (x,()))
+-}
+
+emptySTMRangeMap :: STM (RangeMap TArray a TVar)
+emptySTMRangeMap = RefArray <$>
+                     (newTVar =<<
+                        newListArray (0,-1) [])
+
+-- | a sample RangeMap for easier debugging
+getX :: IO (RangeMap IOArray Word8 IORef)
+getX = RefArray <$>
+        (newIORef =<<
+             newListArray (0,2)
+                          [ listArray (15,20) [15..20]
+                          , listArray (100,105) [100..105]
+                          , listArray (106,107) [106..107]
+                          ])
+-- | a sample RangeMap for easier debugging
+getY :: IO (RangeMap IOArray Word8 IORef)
+getY = RefArray <$>
+        (newIORef =<<
+             newListArray (0,3)
+                          [ listArray (0,5) [0..5]
+                          , listArray (15,20) [15..20]
+                          , listArray (100,105) [100..105]
+                          , listArray (106,107) [106..107]
+                          ])
+
+lookupArray :: RangeArray ra m b ref => Index -> RangeMap ra b ref -> m (Either OuterIndex (OuterIndex,InnerArray b))
+lookupArray i r = do
+    ra <- readRefArray r
+    (zr,nr) <- getBounds ra -- bounds of mutable range array
+    let (dr,mr) = (nr+1 - zr) `divMod` 2
+    lookupArrayHelper i r (zr+dr+mr-1) zr nr
+
+lookupArrayHelper :: RangeArray ra m b ref => Index -> RangeMap ra b ref
+                                       -> OuterIndex{- current position  -}
+                                       -> OuterIndex{- smallest possible -}
+                                       -> OuterIndex{- largest possible  -}
+                                       -> m (Either OuterIndex (OuterIndex,InnerArray b))
+lookupArrayHelper i r pos min max = do
+    {- trace ("lookupArrayHelper " ++ show i ++ " "
+                                ++ "ra "
+                                ++ show pos ++ " "
+                                ++ show min ++ " "
+                                ++ show max) (return ()) -}
+    ra <- readRefArray r
+    ca <- MA.readArray ra pos -- current array
+    let beforeOrAfter i (x,y) | i < x = LT
+        beforeOrAfter i (x,y) | i > y = GT
+        beforeOrAfter _ _ = EQ
+        avg a b = (a + b) `divMod` 2
+        isUnequalMod2 a b = if a `mod` 2 /= b `mod` 2 then 1 else 0
+        f a b recurse finish
+                = let (pos',r) = avg a b
+                      u = isUnequalMod2 r (max - min) {- trace ("u = " ++ show t
+                                                                       ++ " min=" ++ show min
+                                                                       ++ " max=" ++ show max
+                                                                       ++ " pos'=" ++ show pos'
+                                                                       ++ " r=" ++ show r
+                                                                       ) t -}
+                      in if max - min + u > 1 && pos' /= pos then recurse pos' r else finish
+        s = "beforeOrAfter " ++ show i ++ " " ++ show (bounds ca) ++ " --> "
+        checkAndReturn pos = do
+            boundsRA <- getBounds ra
+            case beforeOrAfter pos boundsRA of
+                EQ -> do
+                    a <- MA.readArray ra pos
+                    {- trace ("checkAndReturn " ++ show pos ++ " bounds a= " ++ show (bounds a)) (return ()) -}
+                    case beforeOrAfter i (bounds a) of
+                        EQ -> {- trace "EQ" $ -} return (Right (pos,a))
+                        LT -> {- trace "LT" $ -} return (Left pos)
+                        GT -> {- trace "GT" $ -} return (Left (pos+1))
+                LT -> {- trace "LT" $ -} return (Left pos)
+                GT -> {- trace "GT" $ -} return (Left (pos+1))
+    case beforeOrAfter i (bounds ca) of
+        GT -> {- trace (s ++ "GT") $ -} f pos max (\pos' r' -> lookupArrayHelper i r (pos'+r') pos max) (checkAndReturn (pos + 1))
+        LT -> {- trace (s ++ "LT") $ -} f min pos (\pos' r' -> lookupArrayHelper i r pos'      min pos) (checkAndReturn pos)
+        EQ -> {- trace (s ++ "EQ") $ -} return (Right (pos,ca))
+
+insertWhereItGoes :: RangeArray ra m e ref => InnerArray e -> RangeMap ra e ref -> m (Either (OuterIndex, InnerArray e) ())
+insertWhereItGoes e r = do
+    let (i,j) = bounds e
+    outerArray <- readRefArray r
+    (outerZ,outerN) <- MA.getBounds outerArray
+    let inside x (low,hi) = x >= low && x <= hi -- flip inRange
+    lr <- lookupArray i r
+    case lr of
+        Left ii ->
+            trace "(insertWhereItGoes) Left ii case"
+                  $if ii <= outerN -- is there a next array?
+                    then do
+                        y <- MA.readArray outerArray (ii)
+                        let boundsy = show (bounds y)
+                            insideStr = show j ++ " inside " ++ boundsy
+                            outsideStr = show j ++ " outside " ++ boundsy
+                        if j `inside` bounds y -- does the final bound of inserted array overlap next array?
+                            then trace insideStr  $ return (Left (ii,y)) -- TODO, actually could shrink y or e
+                            else trace outsideStr $ Right <$> insertArrayAt r ii e
+                    else Right <$> insertArrayAt r ii e
+        Right x ->
+            trace "(insertWhereItGoes) Right x case"
+                  $return (Left x)
+
+lookupInRangeMap :: RangeArray ra m e ref => Index -> RangeMap ra e ref -> m (Maybe e)
+lookupInRangeMap k r = do
+    b <- lookupArray k r
+    case b of
+        Right (_,ar) -> return (Just (ar ! k))
+        Left _ -> return Nothing
+
+
+deleteRange :: RangeArray ra m e ref => (Index,Index)
+                                     -> RangeMap ra e ref
+                                     -> m (Either OuterIndex (OuterIndex,InnerArray e))
+
+deleteRange (z,n) r = do
+    result <- lookupArray z r
+    case result of
+        Left _ -> return result
+        Right (outerIndex,a) | bounds a /= (z,n) -> return (Left outerIndex)
+        Right (outerIndex,a) | bounds a == (z,n) -> do
+           outerArray <- readRefArray r
+           (zz,nn) <- getBounds outerArray
+           as <-   map (\(i,e) -> (if i > outerIndex then i - 1 else i, e))
+               .   filter ((/=outerIndex) . fst)
+               <$> getAssocs outerArray
+           mutAr <- MA.newListArray (zz,nn-1) (map snd as)
+           writeRefArray r mutAr
+           return result