Dear all, I try to use the following to convert [[Int]] to C's int[][] : foreign export stdcall doCompForeign :: CString -> CString -> IO (Ptr (Ptr Int)) doCompForeign :: CString -> CString -> IO (Ptr (Ptr Int)) doCompForeign patraw cnameraw = let pat = peekCString patraw cname = peekCString cnameraw in doCompHelp pat cname doCompHelp :: IO String-> IO String -> IO (Ptr (Ptr Int)) doCompHelp patIO cnameIO = do pat <- patIO cname <- cnameIO if pat Prelude.== "hns" then (doComp hns cname) else if pat Prelude.== "up" then (doComp up cname) else if pat Prelude.== "down" then (doComp down cname) else if pat Prelude.== "hill" then (doComp hill cname) else (doComp hs cname) doComp :: Pattern -> String -> IO (Ptr (Ptr Int)) doComp pat cname = do (tiPrim,b) <- loadTi cname t1 <- getCPUTime let insts = runVMC (solve (1,b) pat) tiPrim newArray (toArray insts) toArray :: [[Int]] -> [(Ptr Int)] toArray lst = toResultant where toResultant = [toArrayRec (lst!!1)] Prelude.++ toArray (tail lst) toArrayRec :: [Int] -> Ptr Int toArrayRec lst = unsafePerformIO (newArray lst) However, it can compile without problem, however I receive the following error when I run it from C code : Heap exhausted; Current maximum heap size is 268435456 bytes (256 Mb); use `+RTS -M<size>' to increase it. What have I done wrong ? Some help please. Thank you in advance for your help and attention. Best Regards, David Lo