make Control.Monad.Instances compilable by nhc98

[haskell-directory.git] / Data / ByteString.hs

diff --git a/Data/ByteString.hs b/Data/ByteString.hs
index 9187ff5..f030970 100644 (file)
--- a/Data/ByteString.hs
+++ b/Data/ByteString.hs
@@ -445,9 +445,28 @@ unpack (PS ps s l) = inlinePerformIO $ withForeignPtr ps $ \p ->
 
 #else
 
+--
+-- Interacting with head/build fusion rule in ghc 6.5. Disable for now
+--
+
 unpack ps = build (unpackFoldr ps)
 {-# INLINE unpack #-}
 
+--
+-- critical this isn't strict in the acc
+-- as it will break in the presence of list fusion. this is a known
+-- issue with seq and rewrite rules
+--
+unpackFoldr :: ByteString -> (Word8 -> a -> a) -> a -> a
+unpackFoldr (PS fp off len) f ch = withPtr fp $ \p -> do
+    let loop q n    _   | q `seq` n `seq` False = undefined -- n.b.
+        loop _ (-1) acc = return acc
+        loop q n    acc = do
+           a <- peekByteOff q n
+           loop q (n-1) (a `f` acc)
+    loop (p `plusPtr` off) (len-1) ch
+{-# INLINE [0] unpackFoldr #-}
+
 unpackList :: ByteString -> [Word8]
 unpackList (PS fp off len) = withPtr fp $ \p -> do
     let STRICT3(loop)
@@ -461,24 +480,6 @@ unpackList (PS fp off len) = withPtr fp $ \p -> do
 "unpack-list"  [1]  forall p  . unpackFoldr p (:) [] = unpackList p
  #-}
 
-unpackFoldr :: ByteString -> (Word8 -> a -> a) -> a -> a
-unpackFoldr (PS fp off len) f ch = withPtr fp $ \p -> do
-    let STRICT3(loop)
-        loop _ (-1) acc = return acc
-        loop q n    acc = do
-           a <- peekByteOff q n
-           loop q (n-1) (a `f` acc)
-    loop (p `plusPtr` off) (len-1) ch
-{-# INLINE [0] unpackFoldr #-}
-
--- TODO just use normal foldr here.
---
--- or
--- unpack xs | null xs = []
---           | otherwise = unsafeHead xs : unpack (unsafeTail xs)
---
--- ?
-
 #endif
 
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