I want to use ForeignObj for large transient data, but Hugs ForeignObj implementation is quite mysterious... Three ForeignObj interfaces are described as such in exts/Foreign.hs. primitive makeForeignObj :: Addr{-x-} -> Addr{-free-} -> IO ForeignObj primitive writeForeignObj :: ForeignObj -> Addr -> IO () primitive eqForeignObj :: ForeignObj -> ForeignObj -> Bool The latter argument of makeForeignObj is a mystery. 1. I thought it is a pointer of function (with type of [void (*)(void *);] ?). foreign import "foo" "newFO" newFO :: IO Addr foreign import "foo" "delFO" delFO :: Addr -> IO () primitive unsafeCoerce "primUnsafeCoerce" :: a -> b newFO >>= (\fo -> makeForeignObj fo (unsafeCoerce delFO)) This code causes an unexpected signal (probably the implementation of Addr -> IO () is different from C form). 2. `foreign label' is valid? foreign import "foo" "newFO" newFO :: IO Addr foreign label "foo" "delFO" delFO :: Addr newFO >>= (\fo -> makeForeignObj fo delFO) No, it isn't. 3. Then I try to get the pointer of delFO directly (Fortunately lcc-win32 3.1 allows internal global variables viewable, however, I suppose other C compilers do not...). foreign import "foo" "newFO" newFO :: IO Addr foreign import "foo" "delFO" delFO :: Addr -> IO () foreign import "foo" "getDelFO" getDelFO :: IO Addr getDelFO >>= (\del -> newFO >>= (\fo -> makeForeignObj fo del)) It works as expected. But I think such description is not appropriate! Variables in DLL are not always viewable by another program. How I should use ForeignObj finalizer in Hugs? -- KAKIHARA Norihiro [The following code was workable in my environment...] ********** main.c ********** #include #include BOOL WINAPI LibMain(HINSTANCE hInstance, DWORD fdwReason, LPVOID lpReserved) { return TRUE; } extern int *newObj(void) { int *i; i = (int*)malloc(sizeof(int)); *i = 5; printf("CREATED %d\n", *i); return i; } static void delObj(int *i) { printf("DELETED %d\n", *i); free(i); } extern void *getDelObj(void) { return (void*)delObj; } ******** foreignObj.hs ********** import Foreign foreign import "foreignObj" "newObj" newObj :: IO Addr foreign import "foreignObj" "getDelObj" getDelObj :: IO Addr test :: IO () test = getDelObj >>=(\del -> newObj >>= (\obj -> makeForeignObj obj del) >>= (\_ -> putStr "End Program"))