1 -----------------------------------------------------------------------------
3 -- Module : Data.Array.Diff
4 -- Copyright : (c) The University of Glasgow 2001
5 -- License : BSD-style (see the file libraries/base/LICENSE)
7 -- Maintainer : libraries@haskell.org
8 -- Stability : experimental
9 -- Portability : non-portable
11 -- Functional arrays with constant-time update.
13 -----------------------------------------------------------------------------
15 module Data.Array.Diff (
19 -- | Diff arrays have an immutable interface, but rely on internal
20 -- updates in place to provide fast functional update operator
23 -- When the '//' operator is applied to a diff array, its contents
24 -- are physically updated in place. The old array silently changes
25 -- its representation without changing the visible behavior:
26 -- it stores a link to the new current array along with the
27 -- difference to be applied to get the old contents.
29 -- So if a diff array is used in a single-threaded style,
30 -- i.e. after '//' application the old version is no longer used,
31 -- @a'!'i@ takes O(1) time and @a '//' d@ takes O(@length d@).
32 -- Accessing elements of older versions gradually becomes slower.
34 -- Updating an array which is not current makes a physical copy.
35 -- The resulting array is unlinked from the old family. So you
36 -- can obtain a version which is guaranteed to be current and
37 -- thus have fast element access by @a '//' []@.
39 -- Possible improvement for the future (not implemented now):
40 -- make it possible to say "I will make an update now, but when
41 -- I later return to the old version, I want it to mutate back
42 -- instead of being copied".
44 IOToDiffArray, -- data IOToDiffArray
45 -- (a :: * -> * -> *) -- internal mutable array
46 -- (i :: *) -- indices
47 -- (e :: *) -- elements
49 -- | Type synonyms for the two most important IO array types.
51 -- Two most important diff array types are fully polymorphic
52 -- lazy boxed DiffArray:
53 DiffArray, -- = IOToDiffArray IOArray
54 -- ...and strict unboxed DiffUArray, working only for elements
55 -- of primitive types but more compact and usually faster:
56 DiffUArray, -- = IOToDiffArray IOUArray
58 -- * Overloaded immutable array interface
60 -- | Module "Data.Array.IArray" provides the interface of diff arrays.
61 -- They are instances of class 'IArray'.
62 module Data.Array.IArray,
64 -- * Low-level interface
66 -- | These are really internal functions, but you will need them
67 -- to make further 'IArray' instances of various diff array types
68 -- (for either more 'MArray' types or more unboxed element types).
69 newDiffArray, readDiffArray, replaceDiffArray
73 ------------------------------------------------------------------------
79 import Data.Array.Base
80 import Data.Array.IArray
83 import Foreign.Ptr ( Ptr, FunPtr )
84 import Foreign.StablePtr ( StablePtr )
85 import Data.Int ( Int8, Int16, Int32, Int64 )
86 #ifdef __GLASGOW_HASKELL__
87 import Data.Word ( Word )
89 import Data.Word ( Word8, Word16, Word32, Word64 )
91 import System.IO.Unsafe ( unsafePerformIO )
92 import Control.Exception ( evaluate )
93 import Control.Concurrent.MVar ( MVar, newMVar, takeMVar, putMVar, readMVar )
95 ------------------------------------------------------------------------
98 -- | An arbitrary 'MArray' type living in the 'IO' monad can be converted
101 newtype IOToDiffArray a i e =
102 DiffArray {varDiffArray :: MVar (DiffArrayData a i e)}
104 -- Internal representation: either a mutable array, or a link to
105 -- another diff array patched with a list of index+element pairs.
106 data DiffArrayData a i e = Current (a i e)
107 | Diff (IOToDiffArray a i e) [(Int, e)]
109 -- | Fully polymorphic lazy boxed diff array.
110 type DiffArray = IOToDiffArray IOArray
112 -- | Strict unboxed diff array, working only for elements
113 -- of primitive types but more compact and usually faster than 'DiffArray'.
114 type DiffUArray = IOToDiffArray IOUArray
116 -- Having 'MArray a e IO' in instance context would require
117 -- -fallow-undecidable-instances, so each instance is separate here.
119 ------------------------------------------------------------------------
120 -- Showing DiffArrays
122 instance (Ix ix, Show ix, Show e) => Show (DiffArray ix e) where
123 showsPrec = showsIArray
125 instance (Ix ix, Show ix) => Show (DiffUArray ix Char) where
126 showsPrec = showsIArray
128 instance (Ix ix, Show ix) => Show (DiffUArray ix Int) where
129 showsPrec = showsIArray
131 instance (Ix ix, Show ix) => Show (DiffUArray ix Word) where
132 showsPrec = showsIArray
134 instance (Ix ix, Show ix) => Show (DiffUArray ix Float) where
135 showsPrec = showsIArray
137 instance (Ix ix, Show ix) => Show (DiffUArray ix Double) where
138 showsPrec = showsIArray
140 instance (Ix ix, Show ix) => Show (DiffUArray ix Int8) where
141 showsPrec = showsIArray
143 instance (Ix ix, Show ix) => Show (DiffUArray ix Int16) where
144 showsPrec = showsIArray
146 instance (Ix ix, Show ix) => Show (DiffUArray ix Int32) where
147 showsPrec = showsIArray
149 instance (Ix ix, Show ix) => Show (DiffUArray ix Int64) where
150 showsPrec = showsIArray
152 instance (Ix ix, Show ix) => Show (DiffUArray ix Word8) where
153 showsPrec = showsIArray
155 instance (Ix ix, Show ix) => Show (DiffUArray ix Word16) where
156 showsPrec = showsIArray
158 instance (Ix ix, Show ix) => Show (DiffUArray ix Word32) where
159 showsPrec = showsIArray
161 instance (Ix ix, Show ix) => Show (DiffUArray ix Word64) where
162 showsPrec = showsIArray
164 ------------------------------------------------------------------------
167 instance HasBounds a => HasBounds (IOToDiffArray a) where
168 bounds a = unsafePerformIO $ boundsDiffArray a
170 instance IArray (IOToDiffArray IOArray) e where
171 unsafeArray lu ies = unsafePerformIO $ newDiffArray lu ies
172 unsafeAt a i = unsafePerformIO $ a `readDiffArray` i
173 unsafeReplace a ies = unsafePerformIO $ a `replaceDiffArray1` ies
175 instance IArray (IOToDiffArray IOUArray) Char where
176 unsafeArray lu ies = unsafePerformIO $ newDiffArray lu ies
177 unsafeAt a i = unsafePerformIO $ a `readDiffArray` i
178 unsafeReplace a ies = unsafePerformIO $ a `replaceDiffArray2` ies
180 instance IArray (IOToDiffArray IOUArray) Int where
181 unsafeArray lu ies = unsafePerformIO $ newDiffArray lu ies
182 unsafeAt a i = unsafePerformIO $ a `readDiffArray` i
183 unsafeReplace a ies = unsafePerformIO $ a `replaceDiffArray2` ies
185 instance IArray (IOToDiffArray IOUArray) Word where
186 unsafeArray lu ies = unsafePerformIO $ newDiffArray lu ies
187 unsafeAt a i = unsafePerformIO $ a `readDiffArray` i
188 unsafeReplace a ies = unsafePerformIO $ a `replaceDiffArray2` ies
190 instance IArray (IOToDiffArray IOUArray) (Ptr a) where
191 unsafeArray lu ies = unsafePerformIO $ newDiffArray lu ies
192 unsafeAt a i = unsafePerformIO $ a `readDiffArray` i
193 unsafeReplace a ies = unsafePerformIO $ a `replaceDiffArray2` ies
195 instance IArray (IOToDiffArray IOUArray) (FunPtr a) where
196 unsafeArray lu ies = unsafePerformIO $ newDiffArray lu ies
197 unsafeAt a i = unsafePerformIO $ a `readDiffArray` i
198 unsafeReplace a ies = unsafePerformIO $ a `replaceDiffArray2` ies
200 instance IArray (IOToDiffArray IOUArray) Float where
201 unsafeArray lu ies = unsafePerformIO $ newDiffArray lu ies
202 unsafeAt a i = unsafePerformIO $ a `readDiffArray` i
203 unsafeReplace a ies = unsafePerformIO $ a `replaceDiffArray2` ies
205 instance IArray (IOToDiffArray IOUArray) Double where
206 unsafeArray lu ies = unsafePerformIO $ newDiffArray lu ies
207 unsafeAt a i = unsafePerformIO $ a `readDiffArray` i
208 unsafeReplace a ies = unsafePerformIO $ a `replaceDiffArray2` ies
210 instance IArray (IOToDiffArray IOUArray) (StablePtr a) where
211 unsafeArray lu ies = unsafePerformIO $ newDiffArray lu ies
212 unsafeAt a i = unsafePerformIO $ a `readDiffArray` i
213 unsafeReplace a ies = unsafePerformIO $ a `replaceDiffArray2` ies
215 instance IArray (IOToDiffArray IOUArray) Int8 where
216 unsafeArray lu ies = unsafePerformIO $ newDiffArray lu ies
217 unsafeAt a i = unsafePerformIO $ a `readDiffArray` i
218 unsafeReplace a ies = unsafePerformIO $ a `replaceDiffArray2` ies
220 instance IArray (IOToDiffArray IOUArray) Int16 where
221 unsafeArray lu ies = unsafePerformIO $ newDiffArray lu ies
222 unsafeAt a i = unsafePerformIO $ a `readDiffArray` i
223 unsafeReplace a ies = unsafePerformIO $ a `replaceDiffArray2` ies
225 instance IArray (IOToDiffArray IOUArray) Int32 where
226 unsafeArray lu ies = unsafePerformIO $ newDiffArray lu ies
227 unsafeAt a i = unsafePerformIO $ a `readDiffArray` i
228 unsafeReplace a ies = unsafePerformIO $ a `replaceDiffArray2` ies
230 instance IArray (IOToDiffArray IOUArray) Int64 where
231 unsafeArray lu ies = unsafePerformIO $ newDiffArray lu ies
232 unsafeAt a i = unsafePerformIO $ a `readDiffArray` i
233 unsafeReplace a ies = unsafePerformIO $ a `replaceDiffArray2` ies
235 instance IArray (IOToDiffArray IOUArray) Word8 where
236 unsafeArray lu ies = unsafePerformIO $ newDiffArray lu ies
237 unsafeAt a i = unsafePerformIO $ a `readDiffArray` i
238 unsafeReplace a ies = unsafePerformIO $ a `replaceDiffArray2` ies
240 instance IArray (IOToDiffArray IOUArray) Word16 where
241 unsafeArray lu ies = unsafePerformIO $ newDiffArray lu ies
242 unsafeAt a i = unsafePerformIO $ a `readDiffArray` i
243 unsafeReplace a ies = unsafePerformIO $ a `replaceDiffArray2` ies
245 instance IArray (IOToDiffArray IOUArray) Word32 where
246 unsafeArray lu ies = unsafePerformIO $ newDiffArray lu ies
247 unsafeAt a i = unsafePerformIO $ a `readDiffArray` i
248 unsafeReplace a ies = unsafePerformIO $ a `replaceDiffArray2` ies
250 instance IArray (IOToDiffArray IOUArray) Word64 where
251 unsafeArray lu ies = unsafePerformIO $ newDiffArray lu ies
252 unsafeAt a i = unsafePerformIO $ a `readDiffArray` i
253 unsafeReplace a ies = unsafePerformIO $ a `replaceDiffArray2` ies
257 ------------------------------------------------------------------------
258 -- The important stuff.
260 newDiffArray :: (MArray a e IO, Ix i)
263 -> IO (IOToDiffArray a i e)
264 newDiffArray (l,u) ies = do
266 sequence_ [unsafeWrite a i e | (i, e) <- ies]
267 var <- newMVar (Current a)
268 return (DiffArray var)
270 readDiffArray :: (MArray a e IO, Ix i)
271 => IOToDiffArray a i e
274 a `readDiffArray` i = do
275 d <- readMVar (varDiffArray a)
277 Current a' -> unsafeRead a' i
278 Diff a' ies -> maybe (readDiffArray a' i) return (lookup i ies)
280 replaceDiffArray :: (MArray a e IO, Ix i)
281 => IOToDiffArray a i e
283 -> IO (IOToDiffArray a i e)
284 a `replaceDiffArray` ies = do
285 d <- takeMVar (varDiffArray a)
287 Current a' -> case ies of
289 -- We don't do the copy when there is nothing to change
290 -- and this is the current version. But see below.
291 putMVar (varDiffArray a) d
294 diff <- sequence [do e <- unsafeRead a' i; return (i, e)
296 sequence_ [unsafeWrite a' i e | (i, e) <- ies]
297 var' <- newMVar (Current a')
298 putMVar (varDiffArray a) (Diff (DiffArray var') diff)
299 return (DiffArray var')
301 -- We still do the copy when there is nothing to change
302 -- but this is not the current version. So you can use
303 -- 'a // []' to make sure that the resulting array has
304 -- fast element access.
305 putMVar (varDiffArray a) d
306 a' <- thawDiffArray a
307 -- thawDiffArray gives a fresh array which we can
309 sequence_ [unsafeWrite a' i e | (i, e) <- ies]
310 var' <- newMVar (Current a')
311 return (DiffArray var')
313 -- The elements of the diff list might recursively reference the
314 -- array, so we must seq them before taking the MVar to avoid
316 replaceDiffArray1 :: (MArray a e IO, Ix i)
317 => IOToDiffArray a i e
319 -> IO (IOToDiffArray a i e)
320 a `replaceDiffArray1` ies = do
321 mapM_ (evaluate . fst) ies
322 a `replaceDiffArray` ies
324 -- If the array contains unboxed elements, then the elements of the
325 -- diff list may also recursively reference the array from inside
326 -- replaceDiffArray, so we must seq them too.
327 replaceDiffArray2 :: (MArray a e IO, Ix i)
328 => IOToDiffArray a i e
330 -> IO (IOToDiffArray a i e)
331 a `replaceDiffArray2` ies = do
332 mapM_ (\(a,b) -> do evaluate a; evaluate b) ies
333 a `replaceDiffArray` ies
336 boundsDiffArray :: (HasBounds a, Ix ix)
337 => IOToDiffArray a ix e
339 boundsDiffArray a = do
340 d <- readMVar (varDiffArray a)
342 Current a' -> return (bounds a')
343 Diff a' _ -> boundsDiffArray a'
345 freezeDiffArray :: (MArray a e IO, Ix ix)
347 -> IO (IOToDiffArray a ix e)
348 freezeDiffArray a = case bounds a of
350 a' <- newArray_ (l,u)
351 sequence_ [unsafeRead a i >>= unsafeWrite a' i | i <- [0 .. rangeSize (l,u) - 1]]
352 var <- newMVar (Current a')
353 return (DiffArray var)
356 "freeze/DiffArray" freeze = freezeDiffArray
359 -- unsafeFreezeDiffArray is really unsafe. Better don't use the old
360 -- array at all after freezing. The contents of the source array will
361 -- be changed when '//' is applied to the resulting array.
363 unsafeFreezeDiffArray :: (MArray a e IO, Ix ix)
365 -> IO (IOToDiffArray a ix e)
366 unsafeFreezeDiffArray a = do
367 var <- newMVar (Current a)
368 return (DiffArray var)
371 "unsafeFreeze/DiffArray" unsafeFreeze = unsafeFreezeDiffArray
374 thawDiffArray :: (MArray a e IO, Ix ix)
375 => IOToDiffArray a ix e
378 d <- readMVar (varDiffArray a)
380 Current a' -> case bounds a' of
382 a'' <- newArray_ (l,u)
383 sequence_ [unsafeRead a' i >>= unsafeWrite a'' i | i <- [0 .. rangeSize (l,u) - 1]]
386 a'' <- thawDiffArray a'
387 sequence_ [unsafeWrite a'' i e | (i, e) <- ies]
391 "thaw/DiffArray" thaw = thawDiffArray
394 -- unsafeThawDiffArray is really unsafe. Better don't use the old
395 -- array at all after thawing. The contents of the resulting array
396 -- will be changed when '//' is applied to the source array.
398 unsafeThawDiffArray :: (MArray a e IO, Ix ix)
399 => IOToDiffArray a ix e
401 unsafeThawDiffArray a = do
402 d <- readMVar (varDiffArray a)
404 Current a' -> return a'
406 a'' <- unsafeThawDiffArray a'
407 sequence_ [unsafeWrite a'' i e | (i, e) <- ies]
411 "unsafeThaw/DiffArray" unsafeThaw = unsafeThawDiffArray