John Meacham wrote:
On Thu, Mar 30, 2006 at 03:50:06AM +0100, Brian Hulley wrote:
where the intention is that the callback will take the width and height of the window and return a RenderM action, the problem is that because the FFI does not allow RenderM to appear in a foreign type.
it should, the types in foreign declarations should "see through" newtypes.
Unfortunately GHC does not seem to support this: foreign import ccall duma_clear :: Word.Word32 -> RenderM () Unacceptable result type in foreign declaration: RenderM () When checking declaration: foreign import ccall safe "static &duma_clear" duma_clear :: GHC.Word.Word32 -> RenderM () even though the FFI spec agrees with you (Section 3.2): The argument types ati produced by fatype must be marshallable foreign types; that is, each ati is either (1) a basic foreign type or (2) a type synonym or renamed datatype of a marshallable foreign type. Moreover, the result type rt produced by frtype must be a marshallable foreign result type; that is, it is either a marshallable foreign type, ... Thus leading to all the messy fiddling about I have to do to use RenderM instead of IO in my imported functions and callbacks. A tool like greencard may solve some of these problems but the problem I would then have is how to incorporate it in my very flaky development environment (I'm just using the plain text editor in Visual C++ with a shortcut bound to a batch file which calls ghc so the build process is all held together by bits of string and sellotape therefore I don't want to complicate it further if at all possible...) By the way, I think I may have been wrong about GHC not optimizing the call to dropRenderM out of the onRender function in my last post, because when I look at the output using -dddump-cmm (instead of -simpl) dropRenderM is not mentioned in the code for onRender (although I'm not an expert at reading cmm output either and it is mentioned in some other places....) Regards, Brian.