Re: [Haskell-cafe] ST not strict enough?

On Wed, Nov 16, 2011 at 2:16 PM, Johan Tibell wrote:

On Wed, Nov 16, 2011 at 12:07 PM, Johan Tibell wrote:

...

On Wed, Nov 16, 2011 at 11:58 AM, Jason Dusek 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.

Just double checked. modifySTRef is too lazy: -- |Mutate the contents of an 'STRef' modifySTRef :: STRef s a -> (a -> a) -> ST s () modifySTRef ref f = writeSTRef ref . f =<< readSTRef ref We need Data.STRef.Strict

We already have one in base - it re-exports Data.STRef in whole :-) http://www.haskell.org/ghc/docs/latest/html/libraries/base/Data-STRef-Strict... Antoine