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.
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