On Wed, Nov 16, 2011 at 11:58 AM, Jason Dusek <jason.dusek@gmail.com> wrote:
diff --git a/Rebuild.hs b/Rebuild.hs
@@ -15,6 +15,7 @@ import Data.STRef
 import Data.String
 import Data.Word

+import Control.DeepSeq
 import Data.Vector.Unboxed (Vector)
 import qualified Data.Vector.Unboxed as Vector (create, length)
 import qualified Data.Vector.Unboxed.Mutable as Vector hiding (length)
@@ -46,8 +47,8 @@ rebuildAsVector bytes        =  byteVector
    n                       <-  readSTRef counter
    return (Vector.unsafeSlice 0 n v)
  writeOneByte v counter b   =  do n <- readSTRef counter
-                                   Vector.unsafeWrite v n b
+                                   w v n b
                                   modifySTRef counter (+!1)
+  (+!) a b                   =  ((+) $!! a) $!! b
+  w v n b = (Vector.unsafeWrite v $!! n) $!! b

+! doesn't work unless modifySTRef is already strict in the result of the function application. You need to write modifySTRef' that seq:s the result of the function application before calling writeSTRef.

-- Johan