--- /dev/null
+{-# LANGUAGE ScopedTypeVariables #-}
+module GC
+ ({- dont export generic versions for high performance ;-) -}) where
+
+import Control.Monad
+
+import Data.Foldable hiding (mapM_)
+
+import Foreign.Ptr
+import Foreign.Marshal.Alloc
+import Foreign.Marshal.Array
+import Foreign.Storable
+import GHC.Int
+
+
+class RefObj a where
+ payload :: a -> IO IntPtr
+ refs :: a -> IO [a]
+ marked :: a -> IO Bool
+ mark :: a -> IO ()
+
+
+instance RefObj (Ptr a) where
+ payload = return . ptrToIntPtr
+ refs = unpackRefs . castPtr
+ marked = markedRef
+ mark = markRef
+
+
+idOff = 0x0
+numberOfObjsOff = 0x4
+fieldsOff = 0xC
+markedOff = 0x8
+
+unpackRefs :: Ptr Int32 -> IO [Ptr b]
+unpackRefs ptr = do --dereference number of objs; mark field skipped via fieldsOffset
+ numberOfObjs <- peekByteOff ptr numberOfObjsOff :: IO Int32
+ mapM (peekElemOff (ptr `plusPtr` fieldsOff)) [0..fromIntegral $ numberOfObjs-1]
+
+markedRef :: Ptr a -> IO Bool
+markedRef ptr = liftM ((/=0) . fromIntegral) (peekByteOff ptr markedOff :: IO Int32)
+
+markRef :: Ptr a -> IO ()
+markRef ptr = pokeByteOff ptr markedOff (1::Int32)
+
+markTree :: RefObj a => a -> IO ()
+markTree root = marked root >>= (`when` continue) . not
+ where continue = mark root >> refs root >>= mapM_ markTree
+
+
+emptyObj id = do mem <- mallocBytes 0xC
+ pokeArray mem [id,0,0::Int32]
+ return mem
+
+twoRefs = do mem <- mallocBytes 0x14
+ -- idOfObj; numberofObj; marked waste memory Int32
+ pokeArray mem [0::Int32,2,0]
+ obj1 <- emptyObj 1
+ obj2 <- emptyObj 2
+ pokeByteOff mem 0xC obj1
+ pokeByteOff mem (0xC+0x4) obj2
+ return mem
+
+