I have been playing around with the extension wrapper and I feel like I am missing something. When I add the following code to Alpha.hs: foreign import stdcall unsafe "dynamic" dyn_glBlendEquationEXTbogus :: Graphics.Rendering.OpenGL.GL.Extensions.Invoker (GLenum -> IO ()) myBlendEquation2 :: GLenum -> IO () myBlendEquation2 val = do ptr <- getProcAddress "EXT" "glBlendEquationEXT" putStr ("Address of glBlendEquationEXT: " ++ (show ptr) ++ "\n") (dyn_glBlendEquationEXTbogus ptr) val things work ok (I replace the action in blendEquation by a print so that blending is enabled without glBlendEquation to be called through the HOpenGL wrapper, and then I call myBlendEquation2 in the keyboard callback to toggle between equations). If I just move that code unchanged into PerFragment.hs, modifying it so that the functions are exported, and importing it explicitely in Alpha.hs, I get an access violation upon calling myBlendEquation2. Am I missing a GHC flag or functionnality to guide the loading of dynamic bits of code ? How does the program know which dll to load ? Yann P.S. The code of my wrapper is a bit different from the one in HsOpenGLExt.h, I was wary of the unsafePerformIO in there, I hope the difference is irrelevent. If it is, tell me why. (I know there is a loss of generality, but for the momment I am trying to just get blendEquation to work)