Hello, since the last time I think that I understand how to manage Ptr, now I woud like to masterize the ForeignPtr in order to let haskell managed the life of my C objects. So I try to create a Geoemtry object like this. -- data Geometry newtype Geometry = Geometry (Ptr Geometry) deriving (Show, Storable) newGeometry :: Factory -> ForeignPtr Geometry newGeometry f = unsafePerformIO $ do geometry <- c_hkl_factory_create_new_geometry f newForeignPtr c_hkl_geometry_free geometry foreign import ccall safe "hkl.h hkl_factory_create_new_geometry" c_hkl_factory_create_new_geometry :: Factory -> IO (Geometry) foreign import ccall safe "hkl.h &hkl_geometry_free" c_hkl_geometry_free :: FunPtr (Geometry -> IO ()) the C signature are HKLAPI HklGeometry *hkl_factory_create_new_geometry(const HklFactory *self) HKL_ARG_NONNULL(1); HKLAPI void hkl_geometry_free(HklGeometry *self) HKL_ARG_NONNULL(1); But when I try to compile this code, I get this error message 1 of 1] Compiling Hkl.C ( src/Hkl/C.hs, dist/build/Hkl/C.o ) src/Hkl/C.hs:51:33: Couldn't match type ‘Geometry’ with ‘Ptr Geometry’ Expected type: GHC.ForeignPtr.FinalizerPtr Geometry Actual type: FunPtr (Geometry -> IO ()) In the first argument of ‘newForeignPtr’, namely ‘c_hkl_geometry_free’ In a stmt of a 'do' block: newForeignPtr c_hkl_geometry_free geometry src/Hkl/C.hs:51:53: Couldn't match expected type ‘Ptr Geometry’ with actual type ‘Geometry’ In the second argument of ‘newForeignPtr’, namely ‘geometry’ In a stmt of a 'do' block: newForeignPtr c_hkl_geometry_free geometry I do not understand what is wrong in my code thanks if you can help Frederic