[Haskell-cafe] c2hs seems to ignore the types I give it when generating foreign import declarations

[Cale Gibbard]

Hello, I've just started writing bindings to the Enlightenment
Foundation Libraries, using c2hs. I've run into the following problem
with the types in the foreign import declarations generated.

In Imlib2.h, there is a function prototype:
int imlib_get_visual_depth(Display * display, Visual * visual);

In Imlib.chs, I have (among other things)
import qualified Graphics.X11.Xlib.Types as Xlib
-- ...
{# fun imlib_get_visual_depth as getVisualDepth { id `Xlib.Display',
id `Xlib.Visual' } -> `Int' #}

I run:
c2hs -k /usr/local/include/Imlib2.h Imlib.chs

and in the resulting Imlib.hs, I get:

--- this part is correct:
getVisualDepth :: Xlib.Display -> Xlib.Visual -> IO (Int)
getVisualDepth a1 a2 =
  let {a1' = id a1} in
  let {a2' = id a2} in
  getVisualDepth'_ a1' a2' >>= \res ->
  let {res' = cIntConv res} in
  return (res')

--- this part is not:
foreign import ccall safe "Imlib.h imlib_get_visual_depth"
  getVisualDepth'_ :: ((Ptr ()) -> ((Ptr ()) -> (IO CInt)))

Why did it choose the type Ptr (), when I gave the type Xlib.Display?
I could do an additional cast, but it will get tedious, as I have a
lot of functions to import, and there shouldn't be any need for it
anyway. As this is, it doesn't typecheck at all. If by hand, I change
it to read:

foreign import ccall safe "Imlib.h imlib_get_visual_depth"
  getVisualDepth'_ :: Xlib.Display -> Xlib.Visual -> IO CInt

(which is what I expected it to produce in the first place) then it
works as expected.

Am I making a grievous error, or is this a bug/lack of a feature?

 - Cale